From: Dave Chinner <dchinner@xxxxxxxxxx>
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: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_log_recover.c | 61 +++++++++++++++++++++++++++---------------------
1 file changed, 35 insertions(+), 26 deletions(-)
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 64e530e..90b756f 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -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 0;
+ 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,
--
1.8.3.2
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