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Subject[patch 78/88] md: fix deadlock when stopping arrays
2.6.28-stable review patch.  If anyone has any objections, please let us know.

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

From: Dan Williams <dan.j.williams@intel.com>

[backport of 5fd3a17ed456637a224cf4ca82b9ad9d005bc8d4]

Resolve a deadlock when stopping redundant arrays, i.e. ones that
require a call to sysfs_remove_group when shutdown. The deadlock is
summarized below:

Thread1 Thread2
------- -------
read sysfs attribute stop array
take mddev lock
sysfs_remove_group
sysfs_get_active
wait for mddev lock
wait for active

Sysrq-w:
--------
mdmon S 00000017 2212 4163 1
f1982ea8 00000046 2dcf6b85 00000017 c0b23100 f2f83ed0 c0b23100 f2f8413c
c0b23100 c0b23100 c0b1fb98 f2f8413c 00000000 f2f8413c c0b23100 f2291ecc
00000002 c0b23100 00000000 00000017 f2f83ed0 f1982eac 00000046 c044d9dd
Call Trace:
[<c044d9dd>] ? debug_mutex_add_waiter+0x1d/0x58
[<c06ef451>] __mutex_lock_common+0x1d9/0x338
[<c06ef451>] ? __mutex_lock_common+0x1d9/0x338
[<c06ef5e3>] mutex_lock_interruptible_nested+0x33/0x3a
[<c0634553>] ? mddev_lock+0x14/0x16
[<c0634553>] mddev_lock+0x14/0x16
[<c0634eda>] md_attr_show+0x2a/0x49
[<c04e9997>] sysfs_read_file+0x93/0xf9
mdadm D 00000017 2812 4177 1
f0401d78 00000046 430456f8 00000017 f0401d58 f0401d20 c0b23100 f2da2c4c
c0b23100 c0b23100 c0b1fb98 f2da2c4c 0a10fc36 00000000 c0b23100 f0401d70
00000003 c0b23100 00000000 00000017 f2da29e0 00000001 00000002 00000000
Call Trace:
[<c06eed1b>] schedule_timeout+0x1b/0x95
[<c06eed1b>] ? schedule_timeout+0x1b/0x95
[<c06eeb97>] ? wait_for_common+0x34/0xdc
[<c044fa8a>] ? trace_hardirqs_on_caller+0x18/0x145
[<c044fbc2>] ? trace_hardirqs_on+0xb/0xd
[<c06eec03>] wait_for_common+0xa0/0xdc
[<c0428c7c>] ? default_wake_function+0x0/0x12
[<c06eeccc>] wait_for_completion+0x17/0x19
[<c04ea620>] sysfs_addrm_finish+0x19f/0x1d1
[<c04e920e>] sysfs_hash_and_remove+0x42/0x55
[<c04eb4db>] sysfs_remove_group+0x57/0x86
[<c0638086>] do_md_stop+0x13a/0x499

This has been there for a while, but is easier to trigger now that mdmon
is closely watching sysfs.

Cc: Neil Brown <neilb@suse.de>
Reported-by: Jacek Danecki <jacek.danecki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

drivers/md/md.c | 27 ++++++++++++++++++++++++---
include/linux/raid/md_k.h | 2 ++
2 files changed, 26 insertions(+), 3 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3694,6 +3694,10 @@ static int do_md_run(mddev_t * mddev)
return err;
}
if (mddev->pers->sync_request) {
+ /* wait for any previously scheduled redundancy groups
+ * to be removed
+ */
+ flush_scheduled_work();
if (sysfs_create_group(&mddev->kobj, &md_redundancy_group))
printk(KERN_WARNING
"md: cannot register extra attributes for %s\n",
@@ -3824,6 +3828,14 @@ static void restore_bitmap_write_access(
spin_unlock(&inode->i_lock);
}

+
+static void sysfs_delayed_rm(struct work_struct *ws)
+{
+ mddev_t *mddev = container_of(ws, mddev_t, del_work);
+
+ sysfs_remove_group(&mddev->kobj, &md_redundancy_group);
+}
+
/* mode:
* 0 - completely stop and dis-assemble array
* 1 - switch to readonly
@@ -3833,6 +3845,7 @@ static int do_md_stop(mddev_t * mddev, i
{
int err = 0;
struct gendisk *disk = mddev->gendisk;
+ int remove_group = 0;

if (atomic_read(&mddev->openers) > is_open) {
printk("md: %s still in use.\n",mdname(mddev));
@@ -3868,10 +3881,9 @@ static int do_md_stop(mddev_t * mddev, i
mddev->queue->merge_bvec_fn = NULL;
mddev->queue->unplug_fn = NULL;
mddev->queue->backing_dev_info.congested_fn = NULL;
- if (mddev->pers->sync_request)
- sysfs_remove_group(&mddev->kobj, &md_redundancy_group);
-
module_put(mddev->pers->owner);
+ if (mddev->pers->sync_request)
+ remove_group = 1;
mddev->pers = NULL;
/* tell userspace to handle 'inactive' */
sysfs_notify_dirent(mddev->sysfs_state);
@@ -3919,6 +3931,15 @@ static int do_md_stop(mddev_t * mddev, i
/* make sure all md_delayed_delete calls have finished */
flush_scheduled_work();

+ /* we can't wait for group removal under mddev_lock as
+ * threads holding the group 'active' need to acquire
+ * mddev_lock before going inactive
+ */
+ if (remove_group) {
+ INIT_WORK(&mddev->del_work, sysfs_delayed_rm);
+ schedule_work(&mddev->del_work);
+ }
+
export_array(mddev);

mddev->array_sectors = 0;
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -245,6 +245,8 @@ struct mddev_s
* file in sysfs.
*/

+ struct work_struct del_work; /* used for delayed sysfs removal */
+
spinlock_t write_lock;
wait_queue_head_t sb_wait; /* for waiting on superblock updates */
atomic_t pending_writes; /* number of active superblock writes */



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