src/patches/suse-2.6.27.31/patches.fixes/dm-avoid-put-table-dm_any_congested

   1 From: Chandra Seetharaman <sekharan@us.ibm.com>
   2 Subject: dm: avoid destroying table in dm_any_congested
   3 References: bnc#457205
   4 Patch-mainline: 2.6.28-rc4
   5 Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
   6
   7 [PATCH 1/3] for bnc 457205. Even though this fix is almost
   8 reverted by 3rd patch in this series, this patch is used as it
   9 fixes a suble bug of calling dm_table_put only when dm_get_table
  10 succeeds. Also this makes code more inline with the mainline.
  11
  12 mainline commit 8a57dfc6f943c92b861c9a19b0c86ddcb2aba768
  13
  14     dm_any_congested() just checks for the DMF_BLOCK_IO and has no
  15     code to make sure that suspend waits for dm_any_congested() to
  16     complete.  This patch adds such a check.
  17
  18     Without it, a race can occur with dm_table_put() attempting to
  19     destroying the table in the wrong thread, the one running
  20     dm_any_congested() which is meant to be quick and return
  21     immediately.
  22
  23     Two examples of problems:
  24     1. Sleeping functions called from congested code, the caller
  25        of which holds a spin lock.
  26     2. An ABBA deadlock between pdflush and multipathd. The two locks
  27        in contention are inode lock and kernel lock.
  28
  29     Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
  30     Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
  31     Signed-off-by: Alasdair G Kergon <agk@redhat.com>
  32
  33 Index: linux-2.6.27/drivers/md/dm.c
  34 ===================================================================
  35 --- linux-2.6.27.orig/drivers/md/dm.c
  36 +++ linux-2.6.27/drivers/md/dm.c
  37 @@ -1640,22 +1640,32 @@ static void dm_unplug_all(struct request
  38
  39  static int dm_any_congested(void *congested_data, int bdi_bits)
  40  {
  41 -       int r;
  42 +       int r = bdi_bits;
  43         struct mapped_device *md = (struct mapped_device *) congested_data;
  44 -       struct dm_table *map = dm_get_table(md);
  45 +       struct dm_table *map;
  46
  47 -       if (!map || test_bit(DMF_BLOCK_IO, &md->flags))
  48 -               r = bdi_bits;
  49 -       else if (dm_request_based(md))
  50 -               /*
  51 -                * Request-based dm cares about only own queue for
  52 -                * the query about congestion status of request_queue
  53 -                */
  54 -               r = md->queue->backing_dev_info.state & bdi_bits;
  55 -       else
  56 -               r = dm_table_any_congested(map, bdi_bits);
  57 +       atomic_inc(&md->pending);
  58 +
  59 +       if (!test_bit(DMF_BLOCK_IO, &md->flags)) {
  60 +               map = dm_get_table(md);
  61 +               if (map) {
  62 +                       if (dm_request_based(md))
  63 +                               /*
  64 +                                * Request-based dm cares about only own queue for
  65 +                                * the query about congestion status of request_queue
  66 +                                */
  67 +                               r = md->queue->backing_dev_info.state & bdi_bits;
  68 +                       else
  69 +                               r = dm_table_any_congested(map, bdi_bits);
  70 +                       dm_table_put(map);
  71 +               }
  72 +       }
  73 +
  74 +
  75 +       if (!atomic_dec_return(&md->pending))
  76 +               /* nudge anyone waiting on suspend queue */
  77 +               wake_up(&md->wait);
  78
  79 -       dm_table_put(map);
  80         return r;
  81  }
  82