xfs: don't assert fail on non-async buffers on ioacct decrement

Commit Message

Brian Foster Aug. 3, 2016, 4:12 p.m. UTC

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 <[e-mail]>
Signed-off-by: Brian Foster <[e-mail]>
---
 fs/xfs/xfs_buf.c | 1 -
 1 file changed, 1 deletion(-)

Patch

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 32fc540..b13ff61 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);
 }