The upcoming buftarg I/O accounting mechanism maintains a count of all
buffers that have undergone I/O in the current hold-release cycle.
Certain buffers associated with core infrastructure (e.g., the xfs_mount
superblock buffer, log buffers) are never released, however. This means
that accounting I/O submission on such buffers elevates the buftarg
count indefinitely and could lead to lockup on unmount.
Define a new buffer flag to explicitly exclude buffers from buftarg I/O
accounting. Set the flag on the superblock and associated log buffers.
Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
---
fs/xfs/xfs_buf.h | 1 +
fs/xfs/xfs_log.c | 4 +++-
fs/xfs/xfs_mount.c | 12 +++++++-----
3 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index a3c7ba4..9e1cca7 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -43,6 +43,7 @@ typedef enum {
#define XBF_READ (1 << 0) /* buffer intended for reading from device */
#define XBF_WRITE (1 << 1) /* buffer intended for writing to device */
#define XBF_READ_AHEAD (1 << 2) /* asynchronous read-ahead */
+#define XBF_NO_IOACCT (1 << 3) /* bypass I/O accounting (non-LRU bufs) */
#define XBF_ASYNC (1 << 4) /* initiator will not wait for completion */
#define XBF_DONE (1 << 5) /* all pages in the buffer uptodate */
#define XBF_STALE (1 << 6) /* buffer has been staled, do not find it */
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 63dad9e..4af0fb0 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1427,7 +1427,8 @@ xlog_alloc_log(
ASSERT(xfs_buf_islocked(bp));
xfs_buf_unlock(bp);
- /* use high priority wq for log I/O completion */
+ /* disable accounting and use high priority wq for log I/O completion */
+ bp->b_flags |= XBF_NO_IOACCT;
bp->b_ioend_wq = mp->m_log_workqueue;
bp->b_iodone = xlog_iodone;
log->l_xbuf = bp;
@@ -1457,6 +1458,7 @@ xlog_alloc_log(
BTOBB(log->l_iclog_size), 0);
if (!bp)
goto out_free_iclog;
+ bp->b_flags |= XBF_NO_IOACCT;
ASSERT(xfs_buf_islocked(bp));
xfs_buf_unlock(bp);
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index e39b023..a9234a2 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -272,13 +272,15 @@ xfs_readsb(
buf_ops = NULL;
/*
- * Allocate a (locked) buffer to hold the superblock.
- * This will be kept around at all times to optimize
- * access to the superblock.
+ * Allocate a (locked) buffer to hold the superblock. This will be kept
+ * around at all times to optimize access to the superblock. Therefore,
+ * set XBF_NO_IOACCT to make sure it doesn't hold the buftarg count
+ * elevated.
*/
reread:
- error = xfs_buf_read_uncached(mp->m_ddev_targp, XFS_SB_DADDR,
- BTOBB(sector_size), 0, &bp, buf_ops);
+ error = xfs_buf_read_uncached_flags(mp->m_ddev_targp, XFS_SB_DADDR,
+ BTOBB(sector_size), 0, &bp, buf_ops,
+ XBF_NO_IOACCT);
if (error) {
if (loud)
xfs_warn(mp, "SB validate failed with error %d.",
error);
--
2.5.5
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