xfs: use dedicated log worker wq to avoid deadlock with cil wq

The log covering background task used to be part of the xfssyncd
workqueue. That workqueue was removed as of commit 5889608df ("xfs:
syncd workqueue is no more") and the associated work item scheduled
to the xfs-log wq. The latter is used for log buffer I/O completion.

Since xfs_log_worker() can invoke a log flush, a deadlock is
possible between the xfs-log and xfs-cil workqueues. Consider the
following codepath from xfs_log_worker():

xfs_log_worker()
  xfs_log_force()
    _xfs_log_force()
      xlog_cil_force()
        xlog_cil_force_lsn()
          xlog_cil_push_now()
            flush_work()

The above is in xfs-log wq context and blocked waiting on the
completion of an xfs-cil work item. Concurrently, the cil push in
progress can end up blocked here:

xlog_cil_push_work()
  xlog_cil_push()
    xlog_write()
      xlog_state_get_iclog_space()
        xlog_wait(&log->l_flush_wait, ...)

The above is in xfs-cil context waiting on log buffer I/O
completion, which executes in xfs-log wq context. In this scenario
both workqueues are deadlocked waiting on eachother.

Add a new workqueue specifically for the high level log covering and
ail pushing worker, as was the case prior to commit 5889608df.

Diagnosed-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index b1469f0a91a6c04329cb2fff2dc6e9953485a071..bb58cd1873c9b2eba1ac9180d85548c22abbdff5 100644 (file)
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1293,7 +1293,7 @@ void
 xfs_log_work_queue(
        struct xfs_mount        *mp)
 {
-       queue_delayed_work(mp->m_log_workqueue, &mp->m_log->l_work,
+       queue_delayed_work(mp->m_sync_workqueue, &mp->m_log->l_work,
                                msecs_to_jiffies(xfs_syncd_centisecs * 10));
 }
 

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 6db6fd6b82b0ae7eaee47fd88735325734aa51e0..22b2185e93a0c4aa4edcd25411bed006d4fbe715 100644 (file)
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -183,6 +183,7 @@ typedef struct xfs_mount {
        struct workqueue_struct *m_reclaim_workqueue;
        struct workqueue_struct *m_log_workqueue;
        struct workqueue_struct *m_eofblocks_workqueue;
+       struct workqueue_struct *m_sync_workqueue;
 
        /*
         * Generation of the filesysyem layout.  This is incremented by each

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 685c042a120f16a8a9a8dad69d8ee7ce6f9274a0..47d239dcf3f4d46cf73153fdfc9521692b1847bb 100644 (file)
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -877,8 +877,15 @@ xfs_init_mount_workqueues(
        if (!mp->m_eofblocks_workqueue)
                goto out_destroy_log;
 
+       mp->m_sync_workqueue = alloc_workqueue("xfs-sync/%s", WQ_FREEZABLE, 0,
+                                              mp->m_fsname);
+       if (!mp->m_sync_workqueue)
+               goto out_destroy_eofb;
+
        return 0;
 
+out_destroy_eofb:
+       destroy_workqueue(mp->m_eofblocks_workqueue);
 out_destroy_log:
        destroy_workqueue(mp->m_log_workqueue);
 out_destroy_reclaim:
@@ -899,6 +906,7 @@ STATIC void
 xfs_destroy_mount_workqueues(
        struct xfs_mount        *mp)
 {
+       destroy_workqueue(mp->m_sync_workqueue);
        destroy_workqueue(mp->m_eofblocks_workqueue);
        destroy_workqueue(mp->m_log_workqueue);
        destroy_workqueue(mp->m_reclaim_workqueue);