From 4dd3fd7197303739094183b139bae3142a3d55e6 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Wed, 17 Aug 2016 08:30:28 +1000 Subject: xfs: don't assert fail on non-async buffers on ioacct decrement The buffer I/O accounting mechanism tracks async buffers under I/O. As an optimization, the buffer I/O count is incremented only once on the first async I/O for a given hold cycle of a buffer and decremented once the buffer is released to the LRU (or freed). xfs_buf_ioacct_dec() has an ASSERT() check for an XBF_ASYNC buffer, but we have one or two corner cases where a buffer can be submitted for I/O multiple times via different methods in a single hold cycle. If an async I/O occurs first, the I/O count is incremented. If a sync I/O occurs before the hold count drops, XBF_ASYNC is cleared by the time the I/O count is decremented. Remove the async assert check from xfs_buf_ioacct_dec() as this is a perfectly valid scenario. For the purposes of I/O accounting, we really only care about the buffer async state at I/O submission time. Discovered-and-analyzed-by: Dave Chinner Signed-off-by: Brian Foster Reviewed-by: Dave Chinner Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf.c | 1 - 1 file changed, 1 deletion(-) (limited to 'fs/xfs/xfs_buf.c') diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 47a318ce82e0..607cc29bba21 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -115,7 +115,6 @@ xfs_buf_ioacct_dec( if (!(bp->b_flags & _XBF_IN_FLIGHT)) return; - ASSERT(bp->b_flags & XBF_ASYNC); bp->b_flags &= ~_XBF_IN_FLIGHT; percpu_counter_dec(&bp->b_target->bt_io_count); } -- cgit From 800b2694f890cc35a1bda63501fc71c94389d517 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Fri, 26 Aug 2016 16:01:59 +1000 Subject: xfs: prevent dropping ioend completions during buftarg wait xfs_wait_buftarg() waits for all pending I/O, drains the ioend completion workqueue and walks the LRU until all buffers in the cache have been released. This is traditionally an unmount operation` but the mechanism is also reused during filesystem freeze. xfs_wait_buftarg() invokes drain_workqueue() as part of the quiesce, which is intended more for a shutdown sequence in that it indicates to the queue that new operations are not expected once the drain has begun. New work jobs after this point result in a WARN_ON_ONCE() and are otherwise dropped. With filesystem freeze, however, read operations are allowed and can proceed during or after the workqueue drain. If such a read occurs during the drain sequence, the workqueue infrastructure complains about the queued ioend completion work item and drops it on the floor. As a result, the buffer remains on the LRU and the freeze never completes. Despite the fact that the overall buffer cache cleanup is not necessary during freeze, fix up this operation such that it is safe to invoke during non-unmount quiesce operations. Replace the drain_workqueue() call with flush_workqueue(), which runs a similar serialization on pending workqueue jobs without causing new jobs to be dropped. This is safe for unmount as unmount independently locks out new operations by the time xfs_wait_buftarg() is invoked. cc: Signed-off-by: Brian Foster Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner --- fs/xfs/xfs_buf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/xfs/xfs_buf.c') diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c index 607cc29bba21..b5b9bffe3520 100644 --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -1611,7 +1611,7 @@ xfs_wait_buftarg( */ while (percpu_counter_sum(&btp->bt_io_count)) delay(100); - drain_workqueue(btp->bt_mount->m_buf_workqueue); + flush_workqueue(btp->bt_mount->m_buf_workqueue); /* loop until there is nothing left on the lru list. */ while (list_lru_count(&btp->bt_lru)) { -- cgit