From 585e6d8856526a846b90b485abf37ec40e5da1cf Mon Sep 17 00:00:00 2001 From: David Chinner Date: Sat, 10 Feb 2007 18:32:29 +1100 Subject: [PATCH] [XFS] Fix a synchronous buftarg flush deadlock when freezing. At the last stage of a freeze, we flush the buftarg synchronously over and over again until it succeeds twice without skipping any buffers. The delwri list flush skips pinned buffers, but tries to flush all others. It removes the buffers from the delwri list, then tries to lock them one at a time as it traverses the list to issue the I/O. It holds them locked until we issue all of the I/O and then unlocks them once we've waited for it to complete. The problem is that during a freeze, the filesystem may still be doing stuff - like flushing delalloc data buffers - in the background and hence we can be trying to lock buffers that were on the delwri list at the same time. Hence we can get ABBA deadlocks between threads doing allocation and the buftarg flush (freeze) thread. Fix it by skipping locked (and pinned) buffers as we traverse the delwri buffer list. SGI-PV: 957195 SGI-Modid: xfs-linux-melb:xfs-kern:27535a Signed-off-by: David Chinner Signed-off-by: Tim Shimmin --- fs/xfs/linux-2.6/xfs_buf.c | 117 +++++++++++++++++++------------------ 1 file changed, 60 insertions(+), 57 deletions(-) diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c index 4fb01ffdfd1a..946b00bf3841 100644 --- a/fs/xfs/linux-2.6/xfs_buf.c +++ b/fs/xfs/linux-2.6/xfs_buf.c @@ -1679,21 +1679,59 @@ xfsbufd_wakeup( return 0; } +/* + * Move as many buffers as specified to the supplied list + * idicating if we skipped any buffers to prevent deadlocks. + */ +STATIC int +xfs_buf_delwri_split( + xfs_buftarg_t *target, + struct list_head *list, + unsigned long age, + int flags) +{ + xfs_buf_t *bp, *n; + struct list_head *dwq = &target->bt_delwrite_queue; + spinlock_t *dwlk = &target->bt_delwrite_lock; + int skipped = 0; + + INIT_LIST_HEAD(list); + spin_lock(dwlk); + list_for_each_entry_safe(bp, n, dwq, b_list) { + XB_TRACE(bp, "walkq1", (long)xfs_buf_ispin(bp)); + ASSERT(bp->b_flags & XBF_DELWRI); + + if (!xfs_buf_ispin(bp) && !xfs_buf_cond_lock(bp)) { + if (!(flags & XBT_FORCE_FLUSH) && + time_before(jiffies, bp->b_queuetime + age)) { + xfs_buf_unlock(bp); + break; + } + + bp->b_flags &= ~(XBF_DELWRI|_XBF_DELWRI_Q| + _XBF_RUN_QUEUES); + bp->b_flags |= XBF_WRITE; + list_move_tail(&bp->b_list, list); + } else + skipped++; + } + spin_unlock(dwlk); + + return skipped; + +} + STATIC int xfsbufd( - void *data) + void *data) { - struct list_head tmp; - unsigned long age; - xfs_buftarg_t *target = (xfs_buftarg_t *)data; - xfs_buf_t *bp, *n; - struct list_head *dwq = &target->bt_delwrite_queue; - spinlock_t *dwlk = &target->bt_delwrite_lock; - int count; + struct list_head tmp; + xfs_buftarg_t *target = (xfs_buftarg_t *)data; + int count; + xfs_buf_t *bp; current->flags |= PF_MEMALLOC; - INIT_LIST_HEAD(&tmp); do { if (unlikely(freezing(current))) { set_bit(XBT_FORCE_SLEEP, &target->bt_flags); @@ -1705,37 +1743,19 @@ xfsbufd( schedule_timeout_interruptible( xfs_buf_timer_centisecs * msecs_to_jiffies(10)); - count = 0; - age = xfs_buf_age_centisecs * msecs_to_jiffies(10); - spin_lock(dwlk); - list_for_each_entry_safe(bp, n, dwq, b_list) { - XB_TRACE(bp, "walkq1", (long)xfs_buf_ispin(bp)); - ASSERT(bp->b_flags & XBF_DELWRI); - - if (!xfs_buf_ispin(bp) && !xfs_buf_cond_lock(bp)) { - if (!test_bit(XBT_FORCE_FLUSH, - &target->bt_flags) && - time_before(jiffies, - bp->b_queuetime + age)) { - xfs_buf_unlock(bp); - break; - } - - bp->b_flags &= ~(XBF_DELWRI|_XBF_DELWRI_Q| - _XBF_RUN_QUEUES); - bp->b_flags |= XBF_WRITE; - list_move_tail(&bp->b_list, &tmp); - count++; - } - } - spin_unlock(dwlk); + xfs_buf_delwri_split(target, &tmp, + xfs_buf_age_centisecs * msecs_to_jiffies(10), + test_bit(XBT_FORCE_FLUSH, &target->bt_flags) + ? XBT_FORCE_FLUSH : 0); + count = 0; while (!list_empty(&tmp)) { bp = list_entry(tmp.next, xfs_buf_t, b_list); ASSERT(target == bp->b_target); list_del_init(&bp->b_list); xfs_buf_iostrategy(bp); + count++; } if (as_list_len > 0) @@ -1756,40 +1776,23 @@ xfsbufd( */ int xfs_flush_buftarg( - xfs_buftarg_t *target, - int wait) + xfs_buftarg_t *target, + int wait) { - struct list_head tmp; - xfs_buf_t *bp, *n; - int pincount = 0; - struct list_head *dwq = &target->bt_delwrite_queue; - spinlock_t *dwlk = &target->bt_delwrite_lock; + struct list_head tmp; + xfs_buf_t *bp, *n; + int pincount = 0; xfs_buf_runall_queues(xfsdatad_workqueue); xfs_buf_runall_queues(xfslogd_workqueue); - INIT_LIST_HEAD(&tmp); - spin_lock(dwlk); - list_for_each_entry_safe(bp, n, dwq, b_list) { - ASSERT(bp->b_target == target); - ASSERT(bp->b_flags & (XBF_DELWRI | _XBF_DELWRI_Q)); - XB_TRACE(bp, "walkq2", (long)xfs_buf_ispin(bp)); - if (xfs_buf_ispin(bp)) { - pincount++; - continue; - } - - list_move_tail(&bp->b_list, &tmp); - } - spin_unlock(dwlk); + pincount = xfs_buf_delwri_split(target, &tmp, 0, XBT_FORCE_FLUSH); /* * Dropped the delayed write list lock, now walk the temporary list */ list_for_each_entry_safe(bp, n, &tmp, b_list) { - xfs_buf_lock(bp); - bp->b_flags &= ~(XBF_DELWRI|_XBF_DELWRI_Q|_XBF_RUN_QUEUES); - bp->b_flags |= XBF_WRITE; + ASSERT(target == bp->b_target); if (wait) bp->b_flags &= ~XBF_ASYNC; else -- 2.30.2