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

commit 696a562072 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
steinar/wifi_calib_4_9_kernel
Brian Foster 2017-03-28 14:51:44 -07:00 committed by Greg Kroah-Hartman
parent 3890d83805
commit c2ad2dc3d2
3 changed files with 10 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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

@ -872,8 +872,15 @@ 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:
@ -894,6 +901,7 @@ 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);