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Subject[PATCH 3.5 14/96] dm mpath: fix race condition between multipath_dtr and pg_init_done
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3.5.7.29 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Shiva Krishna Merla <shivakrishna.merla@netapp.com>

commit 954a73d5d3073df2231820c718fdd2f18b0fe4c9 upstream.

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>
[ luis: backported to 3.5:
- adjusted context
- bumped version to 1.4.1, not 1.6.0 ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
drivers/md/dm-mpath.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 86a56d8..274354d 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -85,6 +85,7 @@ struct multipath {
unsigned queue_io:1; /* Must we queue all I/O? */
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 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 */
@@ -496,7 +497,8 @@ 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);
@@ -909,10 +911,20 @@ 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_sync(&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)
@@ -1131,7 +1143,7 @@ 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;
@@ -1653,7 +1665,7 @@ out:
*---------------------------------------------------------------*/
static struct target_type multipath_target = {
.name = "multipath",
- .version = {1, 4, 0},
+ .version = {1, 4, 1},
.module = THIS_MODULE,
.ctr = multipath_ctr,
.dtr = multipath_dtr,
--
1.8.3.2


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