v2: Add the xfs_buf_lock to xfs_quiesce_attr().
Add explaination why xfs_buf_lock() is used to wait for write.
xfs_wait_buftarg() does not wait for the completion of the write of the
uncached superblock. This write can race with the shutdown of the log and
causes a panic if the write does not win the race.
During the log write, xfsaild_push() will lock the buffer and set the
XBF_ASYNC flag. Because the XBF_FLAG is set, complete() is not performed
on the buffer's iowait entry, we cannot call xfs_buf_iowait() to wait for
the write to complete. The buffer's lock is held until the write is complete,
so we can block on a xfs_buf_lock() request to be notified that the write
is complete.
Signed-off-by: Mark Tinguely <tinguely@xxxxxxx>
Reviewed-by: Christoph Hellwig<hch@xxxxxx>
---
fs/xfs/xfs_mount.c | 9 +++++++++
fs/xfs/xfs_sync.c | 9 +++++++++
2 files changed, 18 insertions(+)
Index: b/fs/xfs/xfs_mount.c
===================================================================
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1529,6 +1529,15 @@ xfs_unmountfs(
xfs_ail_push_all_sync(mp->m_ail);
xfs_wait_buftarg(mp->m_ddev_targp);
+ /*
+ * The superblock buffer is uncached and xfsaild_push() will lock and
+ * set the XBF_ASYNC flag on the buffer. We cannot do xfs_buf_iowait()
+ * here but a lock on the superblock buffer will block until iodone()
+ * has completed.
+ */
+ xfs_buf_lock(mp->m_sb_bp);
+ xfs_buf_unlock(mp->m_sb_bp);
+
xfs_log_unmount_write(mp);
xfs_log_unmount(mp);
xfs_uuid_unmount(mp);
Index: b/fs/xfs/xfs_sync.c
===================================================================
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -359,6 +359,15 @@ xfs_quiesce_attr(
* added an item to the AIL, thus flush it again.
*/
xfs_ail_push_all_sync(mp->m_ail);
+
+ /*
+ * The superblock buffer is uncached and xfsaild_push() will lock and
+ * set the XBF_ASYNC flag on the buffer. We cannot do xfs_buf_iowait()
+ * here but a lock on the superblock buffer will block until iodone()
+ * has completed.
+ */
+ xfs_buf_lock(mp->m_sb_bp);
+ xfs_buf_unlock(mp->m_sb_bp);
}
static void
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