This is a note to let you know that I've just added the patch titled
dm: allocate a special workqueue for deferred device removal
to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-allocate-a-special-workqueue-for-deferred-device-removal.patch
and it can be found in the queue-3.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From acfe0ad74d2e1bfc81d1d7bf5e15b043985d3650 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Date: Sat, 14 Jun 2014 13:44:31 -0400
Subject: dm: allocate a special workqueue for deferred device removal
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
commit acfe0ad74d2e1bfc81d1d7bf5e15b043985d3650 upstream.
The commit 2c140a246dc ("dm: allow remove to be deferred") introduced a
deferred removal feature for the device mapper. When this feature is
used (by passing a flag DM_DEFERRED_REMOVE to DM_DEV_REMOVE_CMD ioctl)
and the user tries to remove a device that is currently in use, the
device will be removed automatically in the future when the last user
closes it.
Device mapper used the system workqueue to perform deferred removals.
However, some targets (dm-raid1, dm-mpath, dm-stripe) flush work items
scheduled for the system workqueue from their destructor. If the
destructor itself is called from the system workqueue during deferred
removal, it introduces a possible deadlock - the workqueue tries to flush
itself.
Fix this possible deadlock by introducing a new workqueue for deferred
removals. We allocate just one workqueue for all dm targets. The
ability of dm targets to process IOs isn't dependent on deferred removal
of unused targets, so a deadlock due to shared workqueue isn't possible.
Also, cleanup local_init() to eliminate potential for returning success
on failure.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/md/dm.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -54,6 +54,8 @@ static void do_deferred_remove(struct wo
static DECLARE_WORK(deferred_remove_work, do_deferred_remove);
+static struct workqueue_struct *deferred_remove_workqueue;
+
/*
* For bio-based dm.
* One of these is allocated per bio.
@@ -283,16 +285,24 @@ static int __init local_init(void)
if (r)
goto out_free_rq_tio_cache;
+ deferred_remove_workqueue = alloc_workqueue("kdmremove", WQ_UNBOUND, 1);
+ if (!deferred_remove_workqueue) {
+ r = -ENOMEM;
+ goto out_uevent_exit;
+ }
+
_major = major;
r = register_blkdev(_major, _name);
if (r < 0)
- goto out_uevent_exit;
+ goto out_free_workqueue;
if (!_major)
_major = r;
return 0;
+out_free_workqueue:
+ destroy_workqueue(deferred_remove_workqueue);
out_uevent_exit:
dm_uevent_exit();
out_free_rq_tio_cache:
@@ -306,6 +316,7 @@ out_free_io_cache:
static void local_exit(void)
{
flush_scheduled_work();
+ destroy_workqueue(deferred_remove_workqueue);
kmem_cache_destroy(_rq_tio_cache);
kmem_cache_destroy(_io_cache);
@@ -414,7 +425,7 @@ static void dm_blk_close(struct gendisk
if (atomic_dec_and_test(&md->open_count) &&
(test_bit(DMF_DEFERRED_REMOVE, &md->flags)))
- schedule_work(&deferred_remove_work);
+ queue_work(deferred_remove_workqueue, &deferred_remove_work);
dm_put(md);
Patches currently in stable-queue which might be from mpatocka@xxxxxxxxxx are
queue-3.14/dm-allocate-a-special-workqueue-for-deferred-device-removal.patch
queue-3.14/dm-io-fix-a-race-condition-in-the-wake-up-code-for-sync_io.patch
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