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dm mpath: fix race condition between multipath_dtr and pg_init_done

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Whenever multipath_dtr() is happening we must prevent queueing any
further path activation work.  Implement this by adding a new
'pg_init_disabled' flag to the multipath structure that denotes future
path activation work should be skipped if it is set.  By disabling
pg_init and then re-enabling in flush_multipath_work() we also avoid the
potential for pg_init to be initiated while suspending an mpath device.

Without this patch a race condition exists that may result in a kernel
panic:

1) If after pg_init_done() decrements pg_init_in_progress to 0, a call
   to wait_for_pg_init_completion() assumes there are no more pending path
   management commands.
2) If pg_init_required is set by pg_init_done(), due to retryable
   mode_select errors, then process_queued_ios() will again queue the
   path activation work.
3) If free_multipath() completes before activate_path() work is called a
   NULL pointer dereference like the following can be seen when
   accessing members of the recently destructed multipath:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
RIP: 0010:[<ffffffffa003db1b>]  [<ffffffffa003db1b>] activate_path+0x1b/0x30 [dm_multipath]
[<ffffffff81090ac0>] worker_thread+0x170/0x2a0
[<ffffffff81096c80>] ? autoremove_wake_function+0x0/0x40

[switch to disabling pg_init in flush_multipath_work & header edits by Mike Snitzer]
Signed-off-by: Shiva Krishna Merla <shivakrishna.merla@netapp.com>
Reviewed-by: Krishnasamy Somasundaram <somasundaram.krishnasamy@netapp.com>
Tested-by: Speagle Andy <Andy.Speagle@netapp.com>
Acked-by: Junichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Shiva Krishna Merla 2013-10-30 03:26:38 +00:00 committed by Mike Snitzer
parent f36afb3957
commit 954a73d5d3
1 changed files with 15 additions and 3 deletions
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18
drivers/md/dm-mpath.c
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@ -87,6 +87,7 @@ struct multipath {
unsigned queue_if_no_path:1; /* Queue I/O if last path fails? */
unsigned saved_queue_if_no_path:1; /* Saved state during suspension */
unsigned retain_attached_hw_handler:1; /* If there's already a hw_handler present, don't change it. */
unsigned pg_init_disabled:1; /* pg_init is not currently allowed */
unsigned pg_init_retries; /* Number of times to retry pg_init */
unsigned pg_init_count; /* Number of times pg_init called */
@ -497,7 +498,8 @@ static void process_queued_ios(struct work_struct *work)
(!pgpath && !m->queue_if_no_path))
must_queue = 0;
if (m->pg_init_required && !m->pg_init_in_progress && pgpath)
if (m->pg_init_required && !m->pg_init_in_progress && pgpath &&
!m->pg_init_disabled)
__pg_init_all_paths(m);
spin_unlock_irqrestore(&m->lock, flags);
@ -942,10 +944,20 @@ static void multipath_wait_for_pg_init_completion(struct multipath *m)
static void flush_multipath_work(struct multipath *m)
{
unsigned long flags;
spin_lock_irqsave(&m->lock, flags);
m->pg_init_disabled = 1;
spin_unlock_irqrestore(&m->lock, flags);
flush_workqueue(kmpath_handlerd);
multipath_wait_for_pg_init_completion(m);
flush_workqueue(kmultipathd);
flush_work(&m->trigger_event);
spin_lock_irqsave(&m->lock, flags);
m->pg_init_disabled = 0;
spin_unlock_irqrestore(&m->lock, flags);
}
static void multipath_dtr(struct dm_target *ti)
@ -1164,7 +1176,7 @@ static int pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
spin_lock_irqsave(&m->lock, flags);
if (m->pg_init_count <= m->pg_init_retries)
if (m->pg_init_count <= m->pg_init_retries && !m->pg_init_disabled)
m->pg_init_required = 1;
else
limit_reached = 1;
@ -1714,7 +1726,7 @@ out:
*---------------------------------------------------------------*/
static struct target_type multipath_target = {
.name = "multipath",
.version = {1, 5, 1},
.version = {1, 6, 0},
.module = THIS_MODULE,
.ctr = multipath_ctr,
.dtr = multipath_dtr,