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

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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>
This commit is contained in:
Brian Foster 2017-03-28 14:51:44 -07:00 committed by Darrick J. Wong
parent f1c0e20243
commit 696a562072
3 changed files with 10 additions and 1 deletions
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2
fs/xfs/xfs_log.c
View file

@ -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));
}

1
fs/xfs/xfs_mount.h
View file

@ -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

8
fs/xfs/xfs_super.c
View file

@ -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);