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authorChandan Rajendra <chandan@linux.vnet.ibm.com>2016-12-23 15:00:18 +0530
committerDavid Sterba <dsterba@suse.com>2017-01-19 18:01:02 +0100
commit97dcdea076ecef41ea4aaa23d4397c2f622e4265 (patch)
treea851e5d1fec17e990a31866d011ca4771c45e95e /fs/btrfs
parent47b5d64691350e116093c9b47b55ca6b9433bc50 (diff)
Btrfs: Fix deadlock between direct IO and fast fsync
The following deadlock is seen when executing generic/113 test, ---------------------------------------------------------+---------------------------------------------------- Direct I/O task Fast fsync task ---------------------------------------------------------+---------------------------------------------------- btrfs_direct_IO __blockdev_direct_IO do_blockdev_direct_IO do_direct_IO btrfs_get_blocks_direct while (blocks needs to written) get_more_blocks (first iteration) btrfs_get_blocks_direct btrfs_create_dio_extent down_read(&BTRFS_I(inode) >dio_sem) Create and add extent map and ordered extent up_read(&BTRFS_I(inode) >dio_sem) btrfs_sync_file btrfs_log_dentry_safe btrfs_log_inode_parent btrfs_log_inode btrfs_log_changed_extents down_write(&BTRFS_I(inode) >dio_sem) Collect new extent maps and ordered extents wait for ordered extent completion get_more_blocks (second iteration) btrfs_get_blocks_direct btrfs_create_dio_extent down_read(&BTRFS_I(inode) >dio_sem) -------------------------------------------------------------------------------------------------------------- In the above description, Btrfs direct I/O code path has not yet started submitting bios for file range covered by the initial ordered extent. Meanwhile, The fast fsync task obtains the write semaphore and waits for I/O on the ordered extent to get completed. However, the Direct I/O task is now blocked on obtaining the read semaphore. To resolve the deadlock, this commit modifies the Direct I/O code path to obtain the read semaphore before invoking __blockdev_direct_IO(). The semaphore is then given up after __blockdev_direct_IO() returns. This allows the Direct I/O code to complete I/O on all the ordered extents it creates. Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r--fs/btrfs/inode.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 415a6ad5ba22..bed6cf5f67a4 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7215,7 +7215,6 @@ static struct extent_map *btrfs_create_dio_extent(struct inode *inode,
struct extent_map *em = NULL;
int ret;
- down_read(&BTRFS_I(inode)->dio_sem);
if (type != BTRFS_ORDERED_NOCOW) {
em = create_pinned_em(inode, start, len, orig_start,
block_start, block_len, orig_block_len,
@@ -7234,7 +7233,6 @@ static struct extent_map *btrfs_create_dio_extent(struct inode *inode,
em = ERR_PTR(ret);
}
out:
- up_read(&BTRFS_I(inode)->dio_sem);
return em;
}
@@ -8695,6 +8693,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
dio_data.unsubmitted_oe_range_start = (u64)offset;
dio_data.unsubmitted_oe_range_end = (u64)offset;
current->journal_info = &dio_data;
+ down_read(&BTRFS_I(inode)->dio_sem);
} else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
&BTRFS_I(inode)->runtime_flags)) {
inode_dio_end(inode);
@@ -8707,6 +8706,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
iter, btrfs_get_blocks_direct, NULL,
btrfs_submit_direct, flags);
if (iov_iter_rw(iter) == WRITE) {
+ up_read(&BTRFS_I(inode)->dio_sem);
current->journal_info = NULL;
if (ret < 0 && ret != -EIOCBQUEUED) {
if (dio_data.reserve)