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Commit 84a5b730 authored by Dave Chinner's avatar Dave Chinner Committed by Ben Myers
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xfs: don't account buffer cancellation during log recovery readahead 



When doing readhaead in log recovery, we check to see if buffers are
cancelled before doing readahead. If we find a cancelled buffer,
however, we always decrement the reference count we have on it, and
that means that readahead is causing a double decrement of the
cancelled buffer reference count.

This results in log recovery *replaying cancelled buffers* as the
actual recovery pass does not find the cancelled buffer entry in the
commit phase of the second pass across a transaction. On debug
kernels, this results in an ASSERT failure like so:

XFS: Assertion failed: !(flags & XFS_BLF_CANCEL), file: fs/xfs/xfs_log_recover.c, line: 1815

xfstests generic/311 reproduces this ASSERT failure with 100%
reproducability.

Fix it by making readahead only peek at the buffer cancelled state
rather than the full accounting that xlog_check_buffer_cancelled()
does.

Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarBen Myers <bpm@sgi.com>
Signed-off-by: default avatarBen Myers <bpm@sgi.com>
parent 0d0ab120

fs/xfs/xfs_log_recover.c

+35 −26
Original line number Diff line number Diff line
@@ -1769,19 +1769,11 @@ xlog_recover_buffer_pass1( 


/*

 * Check to see whether the buffer being recovered has a corresponding

 * entry in the buffer cancel record table.  If it does then return 1

 * so that it will be cancelled, otherwise return 0.  If the buffer is

 * actually a buffer cancel item (XFS_BLF_CANCEL is set), then decrement

 * the refcount on the entry in the table and remove it from the table

 * if this is the last reference.

 *

 * We remove the cancel record from the table when we encounter its

 * last occurrence in the log so that if the same buffer is re-used

 * again after its last cancellation we actually replay the changes

 * made at that point.

 * entry in the buffer cancel record table. If it is, return the cancel

 * buffer structure to the caller.

 */

STATIC int

xlog_check_buffer_cancelled(

STATIC struct xfs_buf_cancel *

xlog_peek_buffer_cancelled(

	struct xlog		*log,

	xfs_daddr_t		blkno,

	uint			len,
@@ -1790,22 +1782,16 @@ xlog_check_buffer_cancelled( 
	struct list_head	*bucket;

	struct xfs_buf_cancel	*bcp;



	if (log->l_buf_cancel_table == NULL) {

		/*

		 * There is nothing in the table built in pass one,

		 * so this buffer must not be cancelled.

		 */

	if (!log->l_buf_cancel_table) {

		/* empty table means no cancelled buffers in the log */

		ASSERT(!(flags & XFS_BLF_CANCEL));

		return 0;

		return NULL;

	}



	/*

	 * Search for an entry in the  cancel table that matches our buffer.

	 */

	bucket = XLOG_BUF_CANCEL_BUCKET(log, blkno);

	list_for_each_entry(bcp, bucket, bc_list) {

		if (bcp->bc_blkno == blkno && bcp->bc_len == len)

			goto found;

			return bcp;

	}



	/*
@@ -1813,9 +1799,32 @@ xlog_check_buffer_cancelled( 
	 * that the buffer is NOT cancelled.

	 */

	ASSERT(!(flags & XFS_BLF_CANCEL));

	return NULL;

}



/*

 * If the buffer is being cancelled then return 1 so that it will be cancelled,

 * otherwise return 0.  If the buffer is actually a buffer cancel item

 * (XFS_BLF_CANCEL is set), then decrement the refcount on the entry in the

 * table and remove it from the table if this is the last reference.

 *

 * We remove the cancel record from the table when we encounter its last

 * occurrence in the log so that if the same buffer is re-used again after its

 * last cancellation we actually replay the changes made at that point.

 */

STATIC int

xlog_check_buffer_cancelled(

	struct xlog		*log,

	xfs_daddr_t		blkno,

	uint			len,

	ushort			flags)

{

	struct xfs_buf_cancel	*bcp;



	bcp = xlog_peek_buffer_cancelled(log, blkno, len, flags);

	if (!bcp)

		return 0;



found:

	/*

	 * We've go a match, so return 1 so that the recovery of this buffer

	 * is cancelled.  If this buffer is actually a buffer cancel log
@@ -3127,7 +3136,7 @@ xlog_recover_buffer_ra_pass2( 
	struct xfs_buf_log_format	*buf_f = item->ri_buf[0].i_addr;

	struct xfs_mount		*mp = log->l_mp;



	if (xlog_check_buffer_cancelled(log, buf_f->blf_blkno,

	if (xlog_peek_buffer_cancelled(log, buf_f->blf_blkno,

			buf_f->blf_len, buf_f->blf_flags)) {

		return;

	}
@@ -3156,7 +3165,7 @@ xlog_recover_inode_ra_pass2( 
			return;

	}



	if (xlog_check_buffer_cancelled(log, ilfp->ilf_blkno, ilfp->ilf_len, 0))

	if (xlog_peek_buffer_cancelled(log, ilfp->ilf_blkno, ilfp->ilf_len, 0))

		return;



	xfs_buf_readahead(mp->m_ddev_targp, ilfp->ilf_blkno,