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path: root/fs/btrfs/transaction.h
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2018-08-06btrfs: replace get_seconds with new 64bit time APIAllen Pais
The get_seconds() function is deprecated as it truncates the timestamp to 32 bits. Change it to or ktime_get_real_seconds(). Signed-off-by: Allen Pais <allen.lkml@gmail.com> Reviewed-by: David Sterba <dsterba@suse.com> [ update changelog ] Signed-off-by: David Sterba <dsterba@suse.com>
2018-05-30btrfs: drop useless member qgroup_reserved of btrfs_pending_snapshotGu JinXiang
Since there is no more use of qgroup_reserved member in struct btrfs_pending_snapshot, remove it. Signed-off-by: Gu JinXiang <gujx@cn.fujitsu.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-04-18btrfs: qgroup: Commit transaction in advance to reduce early EDQUOTQu Wenruo
Unlike previous method that tries to commit transaction inside qgroup_reserve(), this time we will try to commit transaction using fs_info->transaction_kthread to avoid nested transaction and no need to worry about locking context. Since it's an asynchronous function call and we won't wait for transaction commit, unlike previous method, we must call it before we hit the qgroup limit. So this patch will use the ratio and size of qgroup meta_pertrans reservation as indicator to check if we should trigger a transaction commit. (meta_prealloc won't be cleaned in transaction committ, it's useless anyway) Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-04-12btrfs: replace GPL boilerplate by SPDX -- headersDavid Sterba
Remove GPL boilerplate text (long, short, one-line) and keep the rest, ie. personal, company or original source copyright statements. Add the SPDX header. Unify the include protection macros to match the file names. Signed-off-by: David Sterba <dsterba@suse.com>
2018-03-31btrfs: Remove code referencing unused TRANS_USERSPACENikolay Borisov
Now that the userspace transaction ioctls have been removed, TRANS_USERSPACE is no longer used hence we can remove it. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-03-26btrfs: Document consistency of transaction->io_bgs listNikolay Borisov
The reason why io_bgs can be modified without holding any lock is non-obvious. Document it and reference that documentation from the respective call sites. Signed-off-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-03-26btrfs: Remove unused btrfs_start_transaction_lflush functionNikolay Borisov
Commit 0e8c36a9fd81 ("Btrfs: fix lots of orphan inodes when the space is not enough") changed the way transaction reservation is made in btrfs_evict_node and as a result this function became unused. This has been the status quo for 5 years in which time no one noticed, so I'd say it's safe to assume it's unlikely it will ever be used again. Historical note: there were more attempts to remove the function, the reasoning was missing and only based on some static analysis tool reports. Other reason for rejection was that there seemed to be connection to BTRFS_RESERVE_FLUSH_LIMIT and that would need to be removeed to. This was not correct so removing the function is all we can do. Signed-off-by: Nikolay Borisov <nborisov@suse.com> [ add the note ] Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: reorder btrfs_transaction members for better packingDavid Sterba
There are now 20 bytes of holes, we can reduce that to 4 by minor changes. Moving 'aborted' to the status and flags is also more logical, similar for num_dirty_bgs. The size goes from 432 to 416. Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: use narrower type for btrfs_transaction::num_dirty_bgsDavid Sterba
The u64 is an overkill here, we could not possibly create that many blockgroups in one transaction. Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: reorder btrfs_trans_handle members for better packingDavid Sterba
Recent updates to the structure left some holes, reorder the types so the packing is tight. The size goes from 112 to 104 on 64bit. Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: switch to refcount_t type for btrfs_trans_handle::use_countDavid Sterba
The use_count is a reference counter, we can use the refcount_t type, though we don't use the atomicity. This is not a performance critical code and we could catch the underflows. The type is changed from long, but the number of references will fit an int. Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: remove unused member of btrfs_trans_handleDavid Sterba
Last user was removed in a monster commit a22285a6a32390195235171 ("Btrfs: Integrate metadata reservation with start_transaction") in 2010. Signed-off-by: David Sterba <dsterba@suse.com>
2018-01-22btrfs: switch btrfs_trans_handle::adding_csums to boolDavid Sterba
The semantics of adding_csums matches bool, 'short' was most likely used to save space in a698d0755adb6f2 ("Btrfs: add a type field for the transaction handle"). Signed-off-by: David Sterba <dsterba@suse.com>
2017-04-18btrfs: remove unused qgroup members from btrfs_trans_handleDavid Sterba
The members have been effectively unused since "Btrfs: rework qgroup accounting" (fcebe4562dec83b3), there's no substitute for assert_qgroups_uptodate so it's removed as well. Reviewed-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: David Sterba <dsterba@suse.com>
2017-04-18btrfs: convert btrfs_transaction.use_count from atomic_t to refcount_tElena Reshetova
refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This allows to avoid accidental refcounter overflows that might lead to use-after-free situations. Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com> Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: David Windsor <dwindsor@gmail.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-12-06btrfs: remove root parameter from transaction commit/end routinesJeff Mahoney
Now we only use the root parameter to print the root objectid in a tracepoint. We can use the root parameter from the transaction handle for that. It's also used to join the transaction with async commits, so we remove the comment that it's just for checking. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-12-06btrfs: split btrfs_wait_marked_extents into normal and tree log functionsJeff Mahoney
btrfs_write_and_wait_marked_extents and btrfs_sync_log both call btrfs_wait_marked_extents, which provides a core loop and then handles errors differently based on whether it's it's a log root or not. This means that btrfs_write_and_wait_marked_extents needs to take a root because btrfs_wait_marked_extents requires one, even though it's only used to determine whether the root is a log root. The log root code won't ever call into the transaction commit code using a log root, so we can factor out the core loop and provide the error handling appropriate to each waiter in new routines. This allows us to eventually remove the root argument from btrfs_commit_transaction, and as a result, btrfs_end_transaction. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-12-06btrfs: take an fs_info directly when the root is not used otherwiseJeff Mahoney
There are loads of functions in btrfs that accept a root parameter but only use it to obtain an fs_info pointer. Let's convert those to just accept an fs_info pointer directly. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-09-26btrfs: convert pr_* to btrfs_* where possibleJeff Mahoney
For many printks, we want to know which file system issued the message. This patch converts most pr_* calls to use the btrfs_* versions instead. In some cases, this means adding plumbing to allow call sites access to an fs_info pointer. fs/btrfs/check-integrity.c is left alone for another day. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-07-26btrfs: add btrfs_trans_handle->fs_info pointerJeff Mahoney
btrfs_trans_handle->root is documented as for use for confirming that the root passed in to start the transaction is the same as the one ending it. It's used in several places when an fs_info pointer is needed, so let's just add an fs_info pointer directly. Eventually, the root pointer can be removed. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-06-17btrfs: account for non-CoW'd blocks in btrfs_abort_transactionJeff Mahoney
The test for !trans->blocks_used in btrfs_abort_transaction is insufficient to determine whether it's safe to drop the transaction handle on the floor. btrfs_cow_block, informed by should_cow_block, can return blocks that have already been CoW'd in the current transaction. trans->blocks_used is only incremented for new block allocations. If an operation overlaps the blocks in the current transaction entirely and must abort the transaction, we'll happily let it clean up the trans handle even though it may have modified the blocks and will commit an incomplete operation. In the long-term, I'd like to do closer tracking of when the fs is actually modified so we can still recover as gracefully as possible, but that approach will need some discussion. In the short term, since this is the only code using trans->blocks_used, let's just switch it to a bool indicating whether any blocks were used and set it when should_cow_block returns false. Cc: stable@vger.kernel.org # 3.4+ Signed-off-by: Jeff Mahoney <jeffm@suse.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-05-25btrfs: fix string and comment grammatical issues and typosNicholas D Steeves
Signed-off-by: Nicholas D Steeves <nsteeves@gmail.com> Signed-off-by: David Sterba <dsterba@suse.com>
2016-01-07btrfs: preallocate path for snapshot creation at ioctl timeDavid Sterba
We can also preallocate btrfs_path that's used during pending snapshot creation and avoid another late ENOMEM failure. Signed-off-by: David Sterba <dsterba@suse.com>
2016-01-07btrfs: allocate root item at snapshot ioctl timeDavid Sterba
The actual snapshot creation is delayed until transaction commit. If we cannot get enough memory for the root item there, we have to fail the whole transaction commit which is bad. So we'll allocate the memory at the ioctl call and pass it along with the pending_snapshot struct. The potential ENOMEM will be returned to the caller of snapshot ioctl. Signed-off-by: David Sterba <dsterba@suse.com>
2015-12-10Btrfs: fix unprotected list move from unused_bgs to deleted_bgs listFilipe Manana
As of my previous change titled "Btrfs: fix scrub preventing unused block groups from being deleted", the following warning at extent-tree.c:btrfs_delete_unused_bgs() can be hit when we mount the a filesysten with "-o discard": 10263 void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) 10264 { (...) 10405 if (trimming) { 10406 WARN_ON(!list_empty(&block_group->bg_list)); 10407 spin_lock(&trans->transaction->deleted_bgs_lock); 10408 list_move(&block_group->bg_list, 10409 &trans->transaction->deleted_bgs); 10410 spin_unlock(&trans->transaction->deleted_bgs_lock); 10411 btrfs_get_block_group(block_group); 10412 } (...) This happens because scrub can now add back the block group to the list of unused block groups (fs_info->unused_bgs). This is dangerous because we are moving the block group from the unused block groups list to the list of deleted block groups without holding the lock that protects the source list (fs_info->unused_bgs_lock). The following diagram illustrates how this happens: CPU 1 CPU 2 cleaner_kthread() btrfs_delete_unused_bgs() sees bg X in list fs_info->unused_bgs deletes bg X from list fs_info->unused_bgs scrub_enumerate_chunks() searches device tree using its commit root finds device extent for block group X gets block group X from the tree fs_info->block_group_cache_tree (via btrfs_lookup_block_group()) sets bg X to RO (again) scrub_chunk(bg X) sets bg X back to RW mode adds bg X to the list fs_info->unused_bgs again, since it's still unused and currently not in that list sets bg X to RO mode btrfs_remove_chunk(bg X) --> discard is enabled and bg X is in the fs_info->unused_bgs list again so the warning is triggered --> we move it from that list into the transaction's delete_bgs list, but we can have another task currently manipulating the first list (fs_info->unused_bgs) Fix this by using the same lock (fs_info->unused_bgs_lock) to protect both the list of unused block groups and the list of deleted block groups. This makes it safe and there's not much worry for more lock contention, as this lock is seldom used and only the cleaner kthread adds elements to the list of deleted block groups. The warning goes away too, as this was previously an impossible case (and would have been better a BUG_ON/ASSERT) but it's not impossible anymore. Reproduced with fstest btrfs/073 (using MOUNT_OPTIONS="-o discard"). Signed-off-by: Filipe Manana <fdmanana@suse.com>
2015-11-25Btrfs: use global reserve when deleting unused block group after ENOSPCFilipe Manana
It's possible to reach a state where the cleaner kthread isn't able to start a transaction to delete an unused block group due to lack of enough free metadata space and due to lack of unallocated device space to allocate a new metadata block group as well. If this happens try to use space from the global block group reserve just like we do for unlink operations, so that we don't reach a permanent state where starting a transaction for filesystem operations (file creation, renames, etc) keeps failing with -ENOSPC. Such an unfortunate state was observed on a machine where over a dozen unused data block groups existed and the cleaner kthread was failing to delete them due to ENOSPC error when attempting to start a transaction, and even running balance with a -dusage=0 filter failed with ENOSPC as well. Also unmounting and mounting again the filesystem didn't help. Allowing the cleaner kthread to use the global block reserve to delete the unused data block groups fixed the problem. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Jeff Mahoney <jeffm@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21Merge branch 'allocator-fixes' into for-linus-4.4Chris Mason
Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21Btrfs: don't continue setting up space cache when enospcJosef Bacik
If we hit ENOSPC when setting up a space cache don't bother setting up any of the other space cache's in this transaction, it'll just induce unnecessary latency. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21Btrfs: add a flags field to btrfs_transactionJosef Bacik
I want to set some per transaction flags, so instead of adding yet another int lets just convert the current two int indicators to flags and add a flags field for future use. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21Btrfs: change how we wait for pending ordered extentsJosef Bacik
We have a mechanism to make sure we don't lose updates for ordered extents that were logged in the transaction that is currently running. We add the ordered extent to a transaction list and then the transaction waits on all the ordered extents in that list. However are substantially large file systems this list can be extremely large, and can give us soft lockups, since the ordered extents don't remove themselves from the list when they do complete. To fix this we simply add a counter to the transaction that is incremented any time we have a logged extent that needs to be completed in the current transaction. Then when the ordered extent finally completes it decrements the per transaction counter and wakes up the transaction if we are the last ones. This will eliminate the softlockup. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21btrfs: qgroup: Use new metadata reservation.Qu Wenruo
As we have the new metadata reservation functions, use them to replace the old btrfs_qgroup_reserve() call for metadata. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-10-21btrfs: change num_items type from u64 to unsigned intAlexandru Moise
The value of num_items that start_transaction() ultimately always takes is a small one, so a 64 bit integer is overkill. Also change num_items for btrfs_start_transaction() and btrfs_start_transaction_lflush() as well. Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com> Signed-off-by: David Sterba <dsterba@suse.com>
2015-10-05Btrfs: fix deadlock when finalizing block group creationFilipe Manana
Josef ran into a deadlock while a transaction handle was finalizing the creation of its block groups, which produced the following trace: [260445.593112] fio D ffff88022a9df468 0 8924 4518 0x00000084 [260445.593119] ffff88022a9df468 ffffffff81c134c0 ffff880429693c00 ffff88022a9df488 [260445.593126] ffff88022a9e0000 ffff8803490d7b00 ffff8803490d7b18 ffff88022a9df4b0 [260445.593132] ffff8803490d7af8 ffff88022a9df488 ffffffff8175a437 ffff8803490d7b00 [260445.593137] Call Trace: [260445.593145] [<ffffffff8175a437>] schedule+0x37/0x80 [260445.593189] [<ffffffffa0850f37>] btrfs_tree_lock+0xa7/0x1f0 [btrfs] [260445.593197] [<ffffffff810db7c0>] ? prepare_to_wait_event+0xf0/0xf0 [260445.593225] [<ffffffffa07eac44>] btrfs_lock_root_node+0x34/0x50 [btrfs] [260445.593253] [<ffffffffa07eff6b>] btrfs_search_slot+0x88b/0xa00 [btrfs] [260445.593295] [<ffffffffa08389df>] ? free_extent_buffer+0x4f/0x90 [btrfs] [260445.593324] [<ffffffffa07f1a06>] btrfs_insert_empty_items+0x66/0xc0 [btrfs] [260445.593351] [<ffffffffa07ea94a>] ? btrfs_alloc_path+0x1a/0x20 [btrfs] [260445.593394] [<ffffffffa08403b9>] btrfs_finish_chunk_alloc+0x1c9/0x570 [btrfs] [260445.593427] [<ffffffffa08002ab>] btrfs_create_pending_block_groups+0x11b/0x200 [btrfs] [260445.593459] [<ffffffffa0800964>] do_chunk_alloc+0x2a4/0x2e0 [btrfs] [260445.593491] [<ffffffffa0803815>] find_free_extent+0xa55/0xd90 [btrfs] [260445.593524] [<ffffffffa0803c22>] btrfs_reserve_extent+0xd2/0x220 [btrfs] [260445.593532] [<ffffffff8119fe5d>] ? account_page_dirtied+0xdd/0x170 [260445.593564] [<ffffffffa0803e78>] btrfs_alloc_tree_block+0x108/0x4a0 [btrfs] [260445.593597] [<ffffffffa080c9de>] ? btree_set_page_dirty+0xe/0x10 [btrfs] [260445.593626] [<ffffffffa07eb5cd>] __btrfs_cow_block+0x12d/0x5b0 [btrfs] [260445.593654] [<ffffffffa07ebbff>] btrfs_cow_block+0x11f/0x1c0 [btrfs] [260445.593682] [<ffffffffa07ef8c7>] btrfs_search_slot+0x1e7/0xa00 [btrfs] [260445.593724] [<ffffffffa08389df>] ? free_extent_buffer+0x4f/0x90 [btrfs] [260445.593752] [<ffffffffa07f1a06>] btrfs_insert_empty_items+0x66/0xc0 [btrfs] [260445.593830] [<ffffffffa07ea94a>] ? btrfs_alloc_path+0x1a/0x20 [btrfs] [260445.593905] [<ffffffffa08403b9>] btrfs_finish_chunk_alloc+0x1c9/0x570 [btrfs] [260445.593946] [<ffffffffa08002ab>] btrfs_create_pending_block_groups+0x11b/0x200 [btrfs] [260445.593990] [<ffffffffa0815798>] btrfs_commit_transaction+0xa8/0xb40 [btrfs] [260445.594042] [<ffffffffa085abcd>] ? btrfs_log_dentry_safe+0x6d/0x80 [btrfs] [260445.594089] [<ffffffffa082bc84>] btrfs_sync_file+0x294/0x350 [btrfs] [260445.594115] [<ffffffff8123e29b>] vfs_fsync_range+0x3b/0xa0 [260445.594133] [<ffffffff81023891>] ? syscall_trace_enter_phase1+0x131/0x180 [260445.594149] [<ffffffff8123e35d>] do_fsync+0x3d/0x70 [260445.594169] [<ffffffff81023bb8>] ? syscall_trace_leave+0xb8/0x110 [260445.594187] [<ffffffff8123e600>] SyS_fsync+0x10/0x20 [260445.594204] [<ffffffff8175de6e>] entry_SYSCALL_64_fastpath+0x12/0x71 This happened because the same transaction handle created a large number of block groups and while finalizing their creation (inserting new items and updating existing items in the chunk and device trees) a new metadata extent had to be allocated and no free space was found in the current metadata block groups, which made find_free_extent() attempt to allocate a new block group via do_chunk_alloc(). However at do_chunk_alloc() we ended up allocating a new system chunk too and exceeded the threshold of 2Mb of reserved chunk bytes, which makes do_chunk_alloc() enter the final part of block group creation again (at btrfs_create_pending_block_groups()) and attempt to lock again the root of the chunk tree when it's already write locked by the same task. Similarly we can deadlock on extent tree nodes/leafs if while we are running delayed references we end up creating a new metadata block group in order to allocate a new node/leaf for the extent tree (as part of a CoW operation or growing the tree), as btrfs_create_pending_block_groups inserts items into the extent tree as well. In this case we get the following trace: [14242.773581] fio D ffff880428ca3418 0 3615 3100 0x00000084 [14242.773588] ffff880428ca3418 ffff88042d66b000 ffff88042a03c800 ffff880428ca3438 [14242.773594] ffff880428ca4000 ffff8803e4b20190 ffff8803e4b201a8 ffff880428ca3460 [14242.773600] ffff8803e4b20188 ffff880428ca3438 ffffffff8175a437 ffff8803e4b20190 [14242.773606] Call Trace: [14242.773613] [<ffffffff8175a437>] schedule+0x37/0x80 [14242.773656] [<ffffffffa057ff07>] btrfs_tree_lock+0xa7/0x1f0 [btrfs] [14242.773664] [<ffffffff810db7c0>] ? prepare_to_wait_event+0xf0/0xf0 [14242.773692] [<ffffffffa0519c44>] btrfs_lock_root_node+0x34/0x50 [btrfs] [14242.773720] [<ffffffffa051ef6b>] btrfs_search_slot+0x88b/0xa00 [btrfs] [14242.773750] [<ffffffffa0520a06>] btrfs_insert_empty_items+0x66/0xc0 [btrfs] [14242.773758] [<ffffffff811ef4a2>] ? kmem_cache_alloc+0x1d2/0x200 [14242.773786] [<ffffffffa0520ad1>] btrfs_insert_item+0x71/0xf0 [btrfs] [14242.773818] [<ffffffffa052f292>] btrfs_create_pending_block_groups+0x102/0x200 [btrfs] [14242.773850] [<ffffffffa052f96e>] do_chunk_alloc+0x2ae/0x2f0 [btrfs] [14242.773934] [<ffffffffa0532825>] find_free_extent+0xa55/0xd90 [btrfs] [14242.773998] [<ffffffffa0532c22>] btrfs_reserve_extent+0xc2/0x1d0 [btrfs] [14242.774041] [<ffffffffa0532e38>] btrfs_alloc_tree_block+0x108/0x4a0 [btrfs] [14242.774078] [<ffffffffa051a5cd>] __btrfs_cow_block+0x12d/0x5b0 [btrfs] [14242.774118] [<ffffffffa051abff>] btrfs_cow_block+0x11f/0x1c0 [btrfs] [14242.774155] [<ffffffffa051e8c7>] btrfs_search_slot+0x1e7/0xa00 [btrfs] [14242.774194] [<ffffffffa0528021>] ? __btrfs_free_extent.isra.70+0x2e1/0xcb0 [btrfs] [14242.774235] [<ffffffffa0520a06>] btrfs_insert_empty_items+0x66/0xc0 [btrfs] [14242.774274] [<ffffffffa051994a>] ? btrfs_alloc_path+0x1a/0x20 [btrfs] [14242.774318] [<ffffffffa052c433>] __btrfs_run_delayed_refs+0xbb3/0x1020 [btrfs] [14242.774358] [<ffffffffa052f404>] btrfs_run_delayed_refs.part.78+0x74/0x280 [btrfs] [14242.774391] [<ffffffffa052f627>] btrfs_run_delayed_refs+0x17/0x20 [btrfs] [14242.774432] [<ffffffffa05be236>] commit_cowonly_roots+0x8d/0x2bd [btrfs] [14242.774474] [<ffffffffa059d07f>] ? __btrfs_run_delayed_items+0x1cf/0x210 [btrfs] [14242.774516] [<ffffffffa05adac3>] ? btrfs_qgroup_account_extents+0x83/0x130 [btrfs] [14242.774558] [<ffffffffa0544c40>] btrfs_commit_transaction+0x590/0xb40 [btrfs] [14242.774599] [<ffffffffa0589b9d>] ? btrfs_log_dentry_safe+0x6d/0x80 [btrfs] [14242.774642] [<ffffffffa055ac54>] btrfs_sync_file+0x294/0x350 [btrfs] [14242.774650] [<ffffffff8123e29b>] vfs_fsync_range+0x3b/0xa0 [14242.774657] [<ffffffff81023891>] ? syscall_trace_enter_phase1+0x131/0x180 [14242.774663] [<ffffffff8123e35d>] do_fsync+0x3d/0x70 [14242.774669] [<ffffffff81023bb8>] ? syscall_trace_leave+0xb8/0x110 [14242.774675] [<ffffffff8123e600>] SyS_fsync+0x10/0x20 [14242.774681] [<ffffffff8175de6e>] entry_SYSCALL_64_fastpath+0x12/0x71 Fix this by never recursing into the finalization phase of block group creation and making sure we never trigger the finalization of block group creation while running delayed references. Reported-by: Josef Bacik <jbacik@fb.com> Fixes: 00d80e342c0f ("Btrfs: fix quick exhaustion of the system array in the superblock") Signed-off-by: Filipe Manana <fdmanana@suse.com>
2015-09-22Btrfs: keep dropped roots in cache until transaction commitJosef Bacik
When dropping a snapshot we need to account for the qgroup changes. If we drop the snapshot in all one go then the backref code will fail to find blocks from the snapshot we dropped since it won't be able to find the root in the fs root cache. This can lead to us failing to find refs from other roots that pointed at blocks in the now deleted root. To handle this we need to not remove the fs roots from the cache until after we process the qgroup operations. Do this by adding dropped roots to a list on the transaction, and letting the transaction remove the roots at the same time it drops the commit roots. This will keep all of the backref searching code in sync properly, and fixes a problem Mark was seeing with snapshot delete and qgroups. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Tested-by: Holger Hoffstätte <holger.hoffstaette@googlemail.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-07-29btrfs: add missing discards when unpinning extents with -o discardJeff Mahoney
When we clear the dirty bits in btrfs_delete_unused_bgs for extents in the empty block group, it results in btrfs_finish_extent_commit being unable to discard the freed extents. The block group removal patch added an alternate path to forget extents other than btrfs_finish_extent_commit. As a result, any extents that would be freed when the block group is removed aren't discarded. In my test run, with a large copy of mixed sized files followed by removal, it left nearly 2/3 of extents undiscarded. To clean up the block groups, we add the removed block group onto a list that will be discarded after transaction commit. Signed-off-by: Jeff Mahoney <jeffm@suse.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Tested-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-06-10btrfs: qgroup: Add the ability to skip given qgroup for old/new_roots.Qu Wenruo
This is used by later qgroup fix patches for snapshot. As current snapshot accounting is done by btrfs_qgroup_inherit(), but new extent oriented quota mechanism will account extent from btrfs_copy_root() and other snapshot things, causing wrong result. So add this ability to handle snapshot accounting. Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-06-03Btrfs: fix -ENOSPC when finishing block group creationFilipe Manana
While creating a block group, we often end up getting ENOSPC while updating the chunk tree, which leads to a transaction abortion that produces a trace like the following: [30670.116368] WARNING: CPU: 4 PID: 20735 at fs/btrfs/super.c:260 __btrfs_abort_transaction+0x52/0x106 [btrfs]() [30670.117777] BTRFS: Transaction aborted (error -28) (...) [30670.163567] Call Trace: [30670.163906] [<ffffffff8142fa46>] dump_stack+0x4f/0x7b [30670.164522] [<ffffffff8108b6a2>] ? console_unlock+0x361/0x3ad [30670.165171] [<ffffffff81045ea5>] warn_slowpath_common+0xa1/0xbb [30670.166323] [<ffffffffa035daa7>] ? __btrfs_abort_transaction+0x52/0x106 [btrfs] [30670.167213] [<ffffffff81045f05>] warn_slowpath_fmt+0x46/0x48 [30670.167862] [<ffffffffa035daa7>] __btrfs_abort_transaction+0x52/0x106 [btrfs] [30670.169116] [<ffffffffa03743d7>] btrfs_create_pending_block_groups+0x101/0x130 [btrfs] [30670.170593] [<ffffffffa038426a>] __btrfs_end_transaction+0x84/0x366 [btrfs] [30670.171960] [<ffffffffa038455c>] btrfs_end_transaction+0x10/0x12 [btrfs] [30670.174649] [<ffffffffa036eb6b>] btrfs_check_data_free_space+0x11f/0x27c [btrfs] [30670.176092] [<ffffffffa039450d>] btrfs_fallocate+0x7c8/0xb96 [btrfs] [30670.177218] [<ffffffff812459f2>] ? __this_cpu_preempt_check+0x13/0x15 [30670.178622] [<ffffffff81152447>] vfs_fallocate+0x14c/0x1de [30670.179642] [<ffffffff8116b915>] ? __fget_light+0x2d/0x4f [30670.180692] [<ffffffff81152863>] SyS_fallocate+0x47/0x62 [30670.186737] [<ffffffff81435b32>] system_call_fastpath+0x12/0x17 [30670.187792] ---[ end trace 0373e6b491c4a8cc ]--- This is because we don't do proper space reservation for the chunk block reserve when we have multiple tasks allocating chunks in parallel. So block group creation has 2 phases, and the first phase essentially checks if there is enough space in the system space_info, allocating a new system chunk if there isn't, while the second phase updates the device, extent and chunk trees. However, because the updates to the chunk tree happen in the second phase, if we have N tasks, each with its own transaction handle, allocating new chunks in parallel and if there is only enough space in the system space_info to allocate M chunks, where M < N, none of the tasks ends up allocating a new system chunk in the first phase and N - M tasks will get -ENOSPC when attempting to update the chunk tree in phase 2 if they need to COW any nodes/leafs from the chunk tree. Fix this by doing proper reservation in the chunk block reserve. The issue could be reproduced by running fstests generic/038 in a loop, which eventually triggered the problem. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-04-10Btrfs: allow block group cache writeout outside critical section in commitChris Mason
We loop through all of the dirty block groups during commit and write the free space cache. In order to make sure the cache is currect, we do this while no other writers are allowed in the commit. If a large number of block groups are dirty, this can introduce long stalls during the final stages of the commit, which can block new procs trying to change the filesystem. This commit changes the block group cache writeout to take appropriate locks and allow it to run earlier in the commit. We'll still have to redo some of the block groups, but it means we can get most of the work out of the way without blocking the entire FS. Signed-off-by: Chris Mason <clm@fb.com>
2015-04-10Btrfs: reserve space for block groupsJosef Bacik
This changes our delayed refs calculations to include the space needed to write back dirty block groups. Signed-off-by: Chris Mason <clm@fb.com>
2015-03-26Btrfs: fix metadata inconsistencies after directory fsyncFilipe Manana
We can get into inconsistency between inodes and directory entries after fsyncing a directory. The issue is that while a directory gets the new dentries persisted in the fsync log and replayed at mount time, the link count of the inode that directory entries point to doesn't get updated, staying with an incorrect link count (smaller then the correct value). This later leads to stale file handle errors when accessing (including attempt to delete) some of the links if all the other ones are removed, which also implies impossibility to delete the parent directories, since the dentries can not be removed. Another issue is that (unlike ext3/4, xfs, f2fs, reiserfs, nilfs2), when fsyncing a directory, new files aren't logged (their metadata and dentries) nor any child directories. So this patch fixes this issue too, since it has the same resolution as the incorrect inode link count issue mentioned before. This is very easy to reproduce, and the following excerpt from my test case for xfstests shows how: _scratch_mkfs >> $seqres.full 2>&1 _init_flakey _mount_flakey # Create our main test file and directory. $XFS_IO_PROG -f -c "pwrite -S 0xaa 0 8K" $SCRATCH_MNT/foo | _filter_xfs_io mkdir $SCRATCH_MNT/mydir # Make sure all metadata and data are durably persisted. sync # Add a hard link to 'foo' inside our test directory and fsync only the # directory. The btrfs fsync implementation had a bug that caused the new # directory entry to be visible after the fsync log replay but, the inode # of our file remained with a link count of 1. ln $SCRATCH_MNT/foo $SCRATCH_MNT/mydir/foo_2 # Add a few more links and new files. # This is just to verify nothing breaks or gives incorrect results after the # fsync log is replayed. ln $SCRATCH_MNT/foo $SCRATCH_MNT/mydir/foo_3 $XFS_IO_PROG -f -c "pwrite -S 0xff 0 64K" $SCRATCH_MNT/hello | _filter_xfs_io ln $SCRATCH_MNT/hello $SCRATCH_MNT/mydir/hello_2 # Add some subdirectories and new files and links to them. This is to verify # that after fsyncing our top level directory 'mydir', all the subdirectories # and their files/links are registered in the fsync log and exist after the # fsync log is replayed. mkdir -p $SCRATCH_MNT/mydir/x/y/z ln $SCRATCH_MNT/foo $SCRATCH_MNT/mydir/x/y/foo_y_link ln $SCRATCH_MNT/foo $SCRATCH_MNT/mydir/x/y/z/foo_z_link touch $SCRATCH_MNT/mydir/x/y/z/qwerty # Now fsync only our top directory. $XFS_IO_PROG -c "fsync" $SCRATCH_MNT/mydir # And fsync now our new file named 'hello', just to verify later that it has # the expected content and that the previous fsync on the directory 'mydir' had # no bad influence on this fsync. $XFS_IO_PROG -c "fsync" $SCRATCH_MNT/hello # Simulate a crash/power loss. _load_flakey_table $FLAKEY_DROP_WRITES _unmount_flakey _load_flakey_table $FLAKEY_ALLOW_WRITES _mount_flakey # Verify the content of our file 'foo' remains the same as before, 8192 bytes, # all with the value 0xaa. echo "File 'foo' content after log replay:" od -t x1 $SCRATCH_MNT/foo # Remove the first name of our inode. Because of the directory fsync bug, the # inode's link count was 1 instead of 5, so removing the 'foo' name ended up # deleting the inode and the other names became stale directory entries (still # visible to applications). Attempting to remove or access the remaining # dentries pointing to that inode resulted in stale file handle errors and # made it impossible to remove the parent directories since it was impossible # for them to become empty. echo "file 'foo' link count after log replay: $(stat -c %h $SCRATCH_MNT/foo)" rm -f $SCRATCH_MNT/foo # Now verify that all files, links and directories created before fsyncing our # directory exist after the fsync log was replayed. [ -f $SCRATCH_MNT/mydir/foo_2 ] || echo "Link mydir/foo_2 is missing" [ -f $SCRATCH_MNT/mydir/foo_3 ] || echo "Link mydir/foo_3 is missing" [ -f $SCRATCH_MNT/hello ] || echo "File hello is missing" [ -f $SCRATCH_MNT/mydir/hello_2 ] || echo "Link mydir/hello_2 is missing" [ -f $SCRATCH_MNT/mydir/x/y/foo_y_link ] || \ echo "Link mydir/x/y/foo_y_link is missing" [ -f $SCRATCH_MNT/mydir/x/y/z/foo_z_link ] || \ echo "Link mydir/x/y/z/foo_z_link is missing" [ -f $SCRATCH_MNT/mydir/x/y/z/qwerty ] || \ echo "File mydir/x/y/z/qwerty is missing" # We expect our file here to have a size of 64Kb and all the bytes having the # value 0xff. echo "file 'hello' content after log replay:" od -t x1 $SCRATCH_MNT/hello # Now remove all files/links, under our test directory 'mydir', and verify we # can remove all the directories. rm -f $SCRATCH_MNT/mydir/x/y/z/* rmdir $SCRATCH_MNT/mydir/x/y/z rm -f $SCRATCH_MNT/mydir/x/y/* rmdir $SCRATCH_MNT/mydir/x/y rmdir $SCRATCH_MNT/mydir/x rm -f $SCRATCH_MNT/mydir/* rmdir $SCRATCH_MNT/mydir # An fsck, run by the fstests framework everytime a test finishes, also detected # the inconsistency and printed the following error message: # # root 5 inode 257 errors 2001, no inode item, link count wrong # unresolved ref dir 258 index 2 namelen 5 name foo_2 filetype 1 errors 4, no inode ref # unresolved ref dir 258 index 3 namelen 5 name foo_3 filetype 1 errors 4, no inode ref status=0 exit The expected golden output for the test is: wrote 8192/8192 bytes at offset 0 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) wrote 65536/65536 bytes at offset 0 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) File 'foo' content after log replay: 0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa * 0020000 file 'foo' link count after log replay: 5 file 'hello' content after log replay: 0000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0200000 Which is the output after this patch and when running the test against ext3/4, xfs, f2fs, reiserfs or nilfs2. Without this patch, the test's output is: wrote 8192/8192 bytes at offset 0 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) wrote 65536/65536 bytes at offset 0 XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) File 'foo' content after log replay: 0000000 aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa * 0020000 file 'foo' link count after log replay: 1 Link mydir/foo_2 is missing Link mydir/foo_3 is missing Link mydir/x/y/foo_y_link is missing Link mydir/x/y/z/foo_z_link is missing File mydir/x/y/z/qwerty is missing file 'hello' content after log replay: 0000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff * 0200000 rmdir: failed to remove '/home/fdmanana/btrfs-tests/scratch_1/mydir/x/y/z': No such file or directory rmdir: failed to remove '/home/fdmanana/btrfs-tests/scratch_1/mydir/x/y': No such file or directory rmdir: failed to remove '/home/fdmanana/btrfs-tests/scratch_1/mydir/x': No such file or directory rm: cannot remove '/home/fdmanana/btrfs-tests/scratch_1/mydir/foo_2': Stale file handle rm: cannot remove '/home/fdmanana/btrfs-tests/scratch_1/mydir/foo_3': Stale file handle rmdir: failed to remove '/home/fdmanana/btrfs-tests/scratch_1/mydir': Directory not empty Fsck, without this fix, also complains about the wrong link count: root 5 inode 257 errors 2001, no inode item, link count wrong unresolved ref dir 258 index 2 namelen 5 name foo_2 filetype 1 errors 4, no inode ref unresolved ref dir 258 index 3 namelen 5 name foo_3 filetype 1 errors 4, no inode ref So fix this by logging the inodes that the dentries point to when fsyncing a directory. A test case for xfstests follows. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-02-14btrfs: Fix out-of-space bugZhao Lei
Btrfs will report NO_SPACE when we create and remove files for several times, and we can't write to filesystem until mount it again. Steps to reproduce: 1: Create a single-dev btrfs fs with default option 2: Write a file into it to take up most fs space 3: Delete above file 4: Wait about 100s to let chunk removed 5: goto 2 Script is like following: #!/bin/bash # Recommend 1.2G space, too large disk will make test slow DEV="/dev/sda16" MNT="/mnt/tmp" dev_size="$(lsblk -bn -o SIZE "$DEV")" || exit 2 file_size_m=$((dev_size * 75 / 100 / 1024 / 1024)) echo "Loop write ${file_size_m}M file on $((dev_size / 1024 / 1024))M dev" for ((i = 0; i < 10; i++)); do umount "$MNT" 2>/dev/null; done echo "mkfs $DEV" mkfs.btrfs -f "$DEV" >/dev/null || exit 2 echo "mount $DEV $MNT" mount "$DEV" "$MNT" || exit 2 for ((loop_i = 0; loop_i < 20; loop_i++)); do echo echo "loop $loop_i" echo "dd file..." cmd=(dd if=/dev/zero of="$MNT"/file0 bs=1M count="$file_size_m") "${cmd[@]}" 2>/dev/null || { # NO_SPACE error triggered echo "dd failed: ${cmd[*]}" exit 1 } echo "rm file..." rm -f "$MNT"/file0 || exit 2 for ((i = 0; i < 10; i++)); do df "$MNT" | tail -1 sleep 10 done done Reason: It is triggered by commit: 47ab2a6c689913db23ccae38349714edf8365e0a which is used to remove empty block groups automatically, but the reason is not in that patch. Code before works well because btrfs don't need to create and delete chunks so many times with high complexity. Above bug is caused by many reason, any of them can trigger it. Reason1: When we remove some continuous chunks but leave other chunks after, these disk space should be used by chunk-recreating, but in current code, only first create will successed. Fixed by Forrest Liu <forrestl@synology.com> in: Btrfs: fix find_free_dev_extent() malfunction in case device tree has hole Reason2: contains_pending_extent() return wrong value in calculation. Fixed by Forrest Liu <forrestl@synology.com> in: Btrfs: fix find_free_dev_extent() malfunction in case device tree has hole Reason3: btrfs_check_data_free_space() try to commit transaction and retry allocating chunk when the first allocating failed, but space_info->full is set in first allocating, and prevent second allocating in retry. Fixed in this patch by clear space_info->full in commit transaction. Tested for severial times by above script. Changelog v3->v4: use light weight int instead of atomic_t to record have_remove_bgs in transaction, suggested by: Josef Bacik <jbacik@fb.com> Changelog v2->v3: v2 fixed the bug by adding more commit-transaction, but we only need to reclaim space when we are really have no space for new chunk, noticed by: Filipe David Manana <fdmanana@gmail.com> Actually, our code already have this type of commit-and-retry, we only need to make it working with removed-bgs. v3 fixed the bug with above way. Changelog v1->v2: v1 will introduce a new bug when delete and create chunk in same disk space in same transaction, noticed by: Filipe David Manana <fdmanana@gmail.com> V2 fix this bug by commit transaction after remove block grops. Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com> Suggested-by: Filipe David Manana <fdmanana@gmail.com> Suggested-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com> Signed-off-by: Chris Mason <clm@fb.com>
2015-01-21Btrfs: track dirty block groups on their own listJosef Bacik
Currently any time we try to update the block groups on disk we will walk _all_ block groups and check for the ->dirty flag to see if it is set. This function can get called several times during a commit. So if you have several terabytes of data you will be a very sad panda as we will loop through _all_ of the block groups several times, which makes the commit take a while which slows down the rest of the file system operations. This patch introduces a dirty list for the block groups that we get added to when we dirty the block group for the first time. Then we simply update any block groups that have been dirtied since the last time we called btrfs_write_dirty_block_groups. This allows us to clean up how we write the free space cache out so it is much cleaner. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-11-25Merge branch 'dev/pending-changes' of ↵Chris Mason
git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus
2014-11-21Btrfs: make sure logged extents complete in the current transaction V3Josef Bacik
Liu Bo pointed out that my previous fix would lose the generation update in the scenario I described. It is actually much worse than that, we could lose the entire extent if we lose power right after the transaction commits. Consider the following write extent 0-4k log extent in log tree commit transaction < power fail happens here ordered extent completes We would lose the 0-4k extent because it hasn't updated the actual fs tree, and the transaction commit will reset the log so it isn't replayed. If we lose power before the transaction commit we are save, otherwise we are not. Fix this by keeping track of all extents we logged in this transaction. Then when we go to commit the transaction make sure we wait for all of those ordered extents to complete before proceeding. This will make sure that if we lose power after the transaction commit we still have our data. This also fixes the problem of the improperly updated extent generation. Thanks, cc: stable@vger.kernel.org Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-11-20Btrfs: deal with convert_extent_bit errors to avoid fs corruptionFilipe Manana
When committing a transaction or a log, we look for btree extents that need to be durably persisted by searching for ranges in a io tree that have some bits set (EXTENT_DIRTY or EXTENT_NEW). We then attempt to clear those bits and set the EXTENT_NEED_WAIT bit, with calls to the function convert_extent_bit, and then start writeback for the extents. That function however can return an error (at the moment only -ENOMEM is possible, specially when it does GFP_ATOMIC allocation requests through alloc_extent_state_atomic) - that means the ranges didn't got the EXTENT_NEED_WAIT bit set (or at least not for the whole range), which in turn means a call to btrfs_wait_marked_extents() won't find those ranges for which we started writeback, causing a transaction commit or a log commit to persist a new superblock without waiting for the writeback of extents in that range to finish first. Therefore if a crash happens after persisting the new superblock and before writeback finishes, we have a superblock pointing to roots that weren't fully persisted or roots that point to nodes or leafs that weren't fully persisted, causing all sorts of unexpected/bad behaviour as we endup reading garbage from disk or the content of some node/leaf from a past generation that got cowed or deleted and is no longer valid (for this later case we end up getting error messages like "parent transid verify failed on X wanted Y found Z" when reading btree nodes/leafs from disk). Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-11-12btrfs: add support for processing pending changesDavid Sterba
There are some actions that modify global filesystem state but cannot be performed at the time of request, but later at the transaction commit time when the filesystem is in a known state. For example enabling new incompat features on-the-fly or issuing transaction commit from unsafe contexts (sysfs handlers). Signed-off-by: David Sterba <dsterba@suse.cz>
2014-10-02btrfs: hide typecast to definition of BTRFS_SEND_TRANS_STUBDavid Sterba
Signed-off-by: David Sterba <dsterba@suse.cz>
2014-08-15btrfs: disable strict file flushes for renames and truncatesChris Mason
Truncates and renames are often used to replace old versions of a file with new versions. Applications often expect this to be an atomic replacement, even if they haven't done anything to make sure the new version is fully on disk. Btrfs has strict flushing in place to make sure that renaming over an old file with a new file will fully flush out the new file before allowing the transaction commit with the rename to complete. This ordering means the commit code needs to be able to lock file pages, and there are a few paths in the filesystem where we will try to end a transaction with the page lock held. It's rare, but these things can deadlock. This patch removes the ordered flushes and switches to a best effort filemap_flush like ext4 uses. It's not perfect, but it should fix the deadlocks. Signed-off-by: Chris Mason <clm@fb.com>
2014-06-09Btrfs: add sanity tests for new qgroup accounting codeJosef Bacik
This exercises the various parts of the new qgroup accounting code. We do some basic stuff and do some things with the shared refs to make sure all that code works. I had to add a bunch of infrastructure because I needed to be able to insert items into a fake tree without having to do all the hard work myself, hopefully this will be usefull in the future. Thanks, Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>
2014-04-06Btrfs: remove transaction from sendJosef Bacik
Lets try this again. We can deadlock the box if we send on a box and try to write onto the same fs with the app that is trying to listen to the send pipe. This is because the writer could get stuck waiting for a transaction commit which is being blocked by the send. So fix this by making sure looking at the commit roots is always going to be consistent. We do this by keeping track of which roots need to have their commit roots swapped during commit, and then taking the commit_root_sem and swapping them all at once. Then make sure we take a read lock on the commit_root_sem in cases where we search the commit root to make sure we're always looking at a consistent view of the commit roots. Previously we had problems with this because we would swap a fs tree commit root and then swap the extent tree commit root independently which would cause the backref walking code to screw up sometimes. With this patch we no longer deadlock and pass all the weird send/receive corner cases. Thanks, Reportedy-by: Hugo Mills <hugo@carfax.org.uk> Signed-off-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Chris Mason <clm@fb.com>