src/patches/suse-2.6.27.25/patches.fixes/0004-md-fix-deadlock-when-stopping-arrays.patch

   1 From 5fd3a17ed456637a224cf4ca82b9ad9d005bc8d4 Mon Sep 17 00:00:00 2001
   2 From: Dan Williams <dan.j.williams@intel.com>
   3 Date: Wed, 4 Mar 2009 00:57:25 -0700
   4 Subject: [PATCH] md: fix deadlock when stopping arrays
   5
   6 Resolve a deadlock when stopping redundant arrays, i.e. ones that
   7 require a call to sysfs_remove_group when shutdown.  The deadlock is
   8 summarized below:
   9
  10 Thread1                Thread2
  11 -------                -------
  12 read sysfs attribute   stop array
  13                        take mddev lock
  14                        sysfs_remove_group
  15 sysfs_get_active
  16 wait for mddev lock
  17                        wait for active
  18
  19 Sysrq-w:
  20 --------
  21 mdmon         S 00000017  2212  4163      1
  22   f1982ea8 00000046 2dcf6b85 00000017 c0b23100 f2f83ed0 c0b23100 f2f8413c
  23   c0b23100 c0b23100 c0b1fb98 f2f8413c 00000000 f2f8413c c0b23100 f2291ecc
  24   00000002 c0b23100 00000000 00000017 f2f83ed0 f1982eac 00000046 c044d9dd
  25 Call Trace:
  26   [<c044d9dd>] ? debug_mutex_add_waiter+0x1d/0x58
  27   [<c06ef451>] __mutex_lock_common+0x1d9/0x338
  28   [<c06ef451>] ? __mutex_lock_common+0x1d9/0x338
  29   [<c06ef5e3>] mutex_lock_interruptible_nested+0x33/0x3a
  30   [<c0634553>] ? mddev_lock+0x14/0x16
  31   [<c0634553>] mddev_lock+0x14/0x16
  32   [<c0634eda>] md_attr_show+0x2a/0x49
  33   [<c04e9997>] sysfs_read_file+0x93/0xf9
  34 mdadm         D 00000017  2812  4177      1
  35   f0401d78 00000046 430456f8 00000017 f0401d58 f0401d20 c0b23100 f2da2c4c
  36   c0b23100 c0b23100 c0b1fb98 f2da2c4c 0a10fc36 00000000 c0b23100 f0401d70
  37   00000003 c0b23100 00000000 00000017 f2da29e0 00000001 00000002 00000000
  38 Call Trace:
  39   [<c06eed1b>] schedule_timeout+0x1b/0x95
  40   [<c06eed1b>] ? schedule_timeout+0x1b/0x95
  41   [<c06eeb97>] ? wait_for_common+0x34/0xdc
  42   [<c044fa8a>] ? trace_hardirqs_on_caller+0x18/0x145
  43   [<c044fbc2>] ? trace_hardirqs_on+0xb/0xd
  44   [<c06eec03>] wait_for_common+0xa0/0xdc
  45   [<c0428c7c>] ? default_wake_function+0x0/0x12
  46   [<c06eeccc>] wait_for_completion+0x17/0x19
  47   [<c04ea620>] sysfs_addrm_finish+0x19f/0x1d1
  48   [<c04e920e>] sysfs_hash_and_remove+0x42/0x55
  49   [<c04eb4db>] sysfs_remove_group+0x57/0x86
  50   [<c0638086>] do_md_stop+0x13a/0x499
  51
  52 This has been there for a while, but is easier to trigger now that mdmon
  53 is closely watching sysfs.
  54
  55 Cc: <stable@kernel.org>
  56 Reported-by: Jacek Danecki <jacek.danecki@intel.com>
  57 Signed-off-by: Dan Williams <dan.j.williams@intel.com>
  58 Acked-by: NeilBrown <neilb@suse.de>
  59 ---
  60  drivers/md/md.c |   10 +++++++---
  61  1 file changed, 7 insertions(+), 3 deletions(-)
  62
  63 --- a/drivers/md/md.c
  64 +++ b/drivers/md/md.c
  65 @@ -305,9 +305,14 @@ static inline int mddev_trylock(mddev_t
  66         return mutex_trylock(&mddev->reconfig_mutex);
  67  }
  68
  69 +static struct attribute_group md_redundancy_group;
  70  static inline void mddev_unlock(mddev_t * mddev)
  71  {
  72         mutex_unlock(&mddev->reconfig_mutex);
  73 +       if (unlikely(mddev->private == &md_redundancy_group)) {
  74 +               sysfs_remove_group(&mddev->kobj, &md_redundancy_group);
  75 +               mddev->private = NULL;
  76 +       }
  77
  78         md_wakeup_thread(mddev->thread);
  79  }
  80 @@ -3903,10 +3908,9 @@ static int do_md_stop(mddev_t * mddev, i
  81                         mddev->queue->merge_bvec_fn = NULL;
  82                         mddev->queue->unplug_fn = NULL;
  83                         mddev->queue->backing_dev_info.congested_fn = NULL;
  84 -                       if (mddev->pers->sync_request)
  85 -                               sysfs_remove_group(&mddev->kobj, &md_redundancy_group);
  86 -
  87                         module_put(mddev->pers->owner);
  88 +                       if (mddev->pers->sync_request)
  89 +                               mddev->private = &md_redundancy_group;
  90                         mddev->pers = NULL;
  91                         /* tell userspace to handle 'inactive' */
  92                         sysfs_notify(&mddev->kobj, NULL, "array_state");