From 6fb8a90aa3f2319a25f3396b1e9273300f8903b8 Mon Sep 17 00:00:00 2001 From: Carlos Maiolino Date: Fri, 10 Aug 2012 15:01:51 -0300 Subject: xfs: fix race while discarding buffers [V4] While xfs_buftarg_shrink() is freeing buffers from the dispose list (filled with buffers from lru list), there is a possibility to have xfs_buf_stale() racing with it, and removing buffers from dispose list before xfs_buftarg_shrink() does it. This happens because xfs_buftarg_shrink() handle the dispose list without locking and the test condition in xfs_buf_stale() checks for the buffer being in *any* list: if (!list_empty(&bp->b_lru)) If the buffer happens to be on dispose list, this causes the buffer counter of lru list (btp->bt_lru_nr) to be decremented twice (once in xfs_buftarg_shrink() and another in xfs_buf_stale()) causing a wrong account usage of the lru list. This may cause xfs_buftarg_shrink() to return a wrong value to the memory shrinker shrink_slab(), and such account error may also cause an underflowed value to be returned; since the counter is lower than the current number of items in the lru list, a decrement may happen when the counter is 0, causing an underflow on the counter. The fix uses a new flag field (and a new buffer flag) to serialize buffer handling during the shrink process. The new flag field has been designed to use btp->bt_lru_lock/unlock instead of xfs_buf_lock/unlock mechanism. dchinner, sandeen, aquini and aris also deserve credits for this. Signed-off-by: Carlos Maiolino Reviewed-by: Ben Myers Reviewed-by: Dave Chinner Signed-off-by: Ben Myers --- fs/xfs/xfs_buf.c | 5 ++++- fs/xfs/xfs_buf.h | 41 ++++++++++++++++++++++++----------------- 2 files changed, 28 insertions(+), 18 deletions(-) diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index d7a9dd735e1e..933b7930b863 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -96,6 +96,7 @@ xfs_buf_lru_add( atomic_inc(&bp->b_hold); list_add_tail(&bp->b_lru, &btp->bt_lru); btp->bt_lru_nr++; + bp->b_lru_flags &= ~_XBF_LRU_DISPOSE; } spin_unlock(&btp->bt_lru_lock); } @@ -154,7 +155,8 @@ xfs_buf_stale( struct xfs_buftarg *btp = bp->b_target; spin_lock(&btp->bt_lru_lock); - if (!list_empty(&bp->b_lru)) { + if (!list_empty(&bp->b_lru) && + !(bp->b_lru_flags & _XBF_LRU_DISPOSE)) { list_del_init(&bp->b_lru); btp->bt_lru_nr--; atomic_dec(&bp->b_hold); @@ -1501,6 +1503,7 @@ xfs_buftarg_shrink( */ list_move(&bp->b_lru, &dispose); btp->bt_lru_nr--; + bp->b_lru_flags |= _XBF_LRU_DISPOSE; } spin_unlock(&btp->bt_lru_lock); diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h index d03b73b9604e..7c0b6a0a1557 100644 --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h @@ -38,27 +38,28 @@ typedef enum { XBRW_ZERO = 3, /* Zero target memory */ } xfs_buf_rw_t; -#define XBF_READ (1 << 0) /* buffer intended for reading from device */ -#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */ -#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */ -#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */ -#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */ -#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */ +#define XBF_READ (1 << 0) /* buffer intended for reading from device */ +#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */ +#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */ +#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */ +#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */ +#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */ /* I/O hints for the BIO layer */ -#define XBF_SYNCIO (1 << 10)/* treat this buffer as synchronous I/O */ -#define XBF_FUA (1 << 11)/* force cache write through mode */ -#define XBF_FLUSH (1 << 12)/* flush the disk cache before a write */ +#define XBF_SYNCIO (1 << 10)/* treat this buffer as synchronous I/O */ +#define XBF_FUA (1 << 11)/* force cache write through mode */ +#define XBF_FLUSH (1 << 12)/* flush the disk cache before a write */ /* flags used only as arguments to access routines */ -#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */ -#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */ +#define XBF_TRYLOCK (1 << 16)/* lock requested, but do not wait */ +#define XBF_UNMAPPED (1 << 17)/* do not map the buffer */ /* flags used only internally */ -#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ -#define _XBF_KMEM (1 << 21)/* backed by heap memory */ -#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ -#define _XBF_COMPOUND (1 << 23)/* compound buffer */ +#define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ +#define _XBF_KMEM (1 << 21)/* backed by heap memory */ +#define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ +#define _XBF_COMPOUND (1 << 23)/* compound buffer */ +#define _XBF_LRU_DISPOSE (1 << 24)/* buffer being discarded */ typedef unsigned int xfs_buf_flags_t; @@ -72,12 +73,13 @@ typedef unsigned int xfs_buf_flags_t; { XBF_SYNCIO, "SYNCIO" }, \ { XBF_FUA, "FUA" }, \ { XBF_FLUSH, "FLUSH" }, \ - { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\ + { XBF_TRYLOCK, "TRYLOCK" }, /* should never be set */\ { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ { _XBF_PAGES, "PAGES" }, \ { _XBF_KMEM, "KMEM" }, \ { _XBF_DELWRI_Q, "DELWRI_Q" }, \ - { _XBF_COMPOUND, "COMPOUND" } + { _XBF_COMPOUND, "COMPOUND" }, \ + { _XBF_LRU_DISPOSE, "LRU_DISPOSE" } typedef struct xfs_buftarg { dev_t bt_dev; @@ -124,7 +126,12 @@ typedef struct xfs_buf { xfs_buf_flags_t b_flags; /* status flags */ struct semaphore b_sema; /* semaphore for lockables */ + /* + * concurrent access to b_lru and b_lru_flags are protected by + * bt_lru_lock and not by b_sema + */ struct list_head b_lru; /* lru list */ + xfs_buf_flags_t b_lru_flags; /* internal lru status flags */ wait_queue_head_t b_waiters; /* unpin waiters */ struct list_head b_list; struct xfs_perag *b_pag; /* contains rbtree root */ -- cgit v1.2.3 From 0ba6e5368c302819da7aff537e0d7eff2616c6a6 Mon Sep 17 00:00:00 2001 From: Ben Myers Date: Thu, 13 Sep 2012 16:18:47 -0500 Subject: xfs: stop the sync worker before xfs_unmountfs Cancel work of the xfs_sync_worker before teardown of the log in xfs_unmountfs. This prevents occasional crashes on unmount like so: PID: 21602 TASK: ee9df060 CPU: 0 COMMAND: "kworker/0:3" #0 [c5377d28] crash_kexec at c0292c94 #1 [c5377d80] oops_end at c07090c2 #2 [c5377d98] no_context at c06f614e #3 [c5377dbc] __bad_area_nosemaphore at c06f6281 #4 [c5377df4] bad_area_nosemaphore at c06f629b #5 [c5377e00] do_page_fault at c070b0cb #6 [c5377e7c] error_code (via page_fault) at c070892c EAX: f300c6a8 EBX: f300c6a8 ECX: 000000c0 EDX: 000000c0 EBP: c5377ed0 DS: 007b ESI: 00000000 ES: 007b EDI: 00000001 GS: ffffad20 CS: 0060 EIP: c0481ad0 ERR: ffffffff EFLAGS: 00010246 #7 [c5377eb0] atomic64_read_cx8 at c0481ad0 #8 [c5377ebc] xlog_assign_tail_lsn_locked at f7cc7c6e [xfs] #9 [c5377ed4] xfs_trans_ail_delete_bulk at f7ccd520 [xfs] #10 [c5377f0c] xfs_buf_iodone at f7ccb602 [xfs] #11 [c5377f24] xfs_buf_do_callbacks at f7cca524 [xfs] #12 [c5377f30] xfs_buf_iodone_callbacks at f7cca5da [xfs] #13 [c5377f4c] xfs_buf_iodone_work at f7c718d0 [xfs] #14 [c5377f58] process_one_work at c024ee4c #15 [c5377f98] worker_thread at c024f43d #16 [c5377fbc] kthread at c025326b #17 [c5377fe8] kernel_thread_helper at c070e834 PID: 26653 TASK: e79143b0 CPU: 3 COMMAND: "umount" #0 [cde0fda0] __schedule at c0706595 #1 [cde0fe28] schedule at c0706b89 #2 [cde0fe30] schedule_timeout at c0705600 #3 [cde0fe94] __down_common at c0706098 #4 [cde0fec8] __down at c0706122 #5 [cde0fed0] down at c025936f #6 [cde0fee0] xfs_buf_lock at f7c7131d [xfs] #7 [cde0ff00] xfs_freesb at f7cc2236 [xfs] #8 [cde0ff10] xfs_fs_put_super at f7c80f21 [xfs] #9 [cde0ff1c] generic_shutdown_super at c0333d7a #10 [cde0ff38] kill_block_super at c0333e0f #11 [cde0ff48] deactivate_locked_super at c0334218 #12 [cde0ff58] deactivate_super at c033495d #13 [cde0ff68] mntput_no_expire at c034bc13 #14 [cde0ff7c] sys_umount at c034cc69 #15 [cde0ffa0] sys_oldumount at c034ccd4 #16 [cde0ffb0] system_call at c0707e66 commit 11159a05 added this to xfs_log_unmount and needs to be cleaned up at a later date. Signed-off-by: Ben Myers Reviewed-by: Dave Chinner Reviewed-by: Mark Tinguely --- fs/xfs/xfs_super.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c index bdaf4cb9f4a2..19e2380fb867 100644 --- a/fs/xfs/xfs_super.c +++ b/fs/xfs/xfs_super.c @@ -919,6 +919,7 @@ xfs_fs_put_super( struct xfs_mount *mp = XFS_M(sb); xfs_filestream_unmount(mp); + cancel_delayed_work_sync(&mp->m_sync_work); xfs_unmountfs(mp); xfs_syncd_stop(mp); xfs_freesb(mp); -- cgit v1.2.3