git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 66cb1910df17b38334153462ec8166e48058035f Mon Sep 17 00:00:00 2001
   2 From: Joe Thornber <ejt@redhat.com>
   3 Date: Wed, 30 Oct 2013 17:11:58 +0000
   4 Subject: dm cache: fix a race condition between queuing new migrations and quiescing for a shutdown
   5
   6 From: Joe Thornber <ejt@redhat.com>
   7
   8 commit 66cb1910df17b38334153462ec8166e48058035f upstream.
   9
  10 The code that was trying to do this was inadequate.  The postsuspend
  11 method (in ioctl context), needs to wait for the worker thread to
  12 acknowledge the request to quiesce.  Otherwise the migration count may
  13 drop to zero temporarily before the worker thread realises we're
  14 quiescing.  In this case the target will be taken down, but the worker
  15 thread may have issued a new migration, which will cause an oops when
  16 it completes.
  17
  18 Signed-off-by: Joe Thornber <ejt@redhat.com>
  19 Signed-off-by: Mike Snitzer <snitzer@redhat.com>
  20 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  21
  22 ---
  23  drivers/md/dm-cache-target.c |   54 +++++++++++++++++++++++++++++++------------
  24  1 file changed, 40 insertions(+), 14 deletions(-)
  25
  26 --- a/drivers/md/dm-cache-target.c
  27 +++ b/drivers/md/dm-cache-target.c
  28 @@ -148,6 +148,9 @@ struct cache {
  29         wait_queue_head_t migration_wait;
  30         atomic_t nr_migrations;
  31
  32 +       wait_queue_head_t quiescing_wait;
  33 +       atomic_t quiescing_ack;
  34 +
  35         /*
  36          * cache_size entries, dirty if set
  37          */
  38 @@ -748,8 +751,9 @@ static void cell_defer(struct cache *cac
  39
  40  static void cleanup_migration(struct dm_cache_migration *mg)
  41  {
  42 -       dec_nr_migrations(mg->cache);
  43 +       struct cache *cache = mg->cache;
  44         free_migration(mg);
  45 +       dec_nr_migrations(cache);
  46  }
  47
  48  static void migration_failure(struct dm_cache_migration *mg)
  49 @@ -1346,34 +1350,51 @@ static void writeback_some_dirty_blocks(
  50  /*----------------------------------------------------------------
  51   * Main worker loop
  52   *--------------------------------------------------------------*/
  53 -static void start_quiescing(struct cache *cache)
  54 +static bool is_quiescing(struct cache *cache)
  55  {
  56 +       int r;
  57         unsigned long flags;
  58
  59         spin_lock_irqsave(&cache->lock, flags);
  60 -       cache->quiescing = 1;
  61 +       r = cache->quiescing;
  62         spin_unlock_irqrestore(&cache->lock, flags);
  63 +
  64 +       return r;
  65  }
  66
  67 -static void stop_quiescing(struct cache *cache)
  68 +static void ack_quiescing(struct cache *cache)
  69 +{
  70 +       if (is_quiescing(cache)) {
  71 +               atomic_inc(&cache->quiescing_ack);
  72 +               wake_up(&cache->quiescing_wait);
  73 +       }
  74 +}
  75 +
  76 +static void wait_for_quiescing_ack(struct cache *cache)
  77 +{
  78 +       wait_event(cache->quiescing_wait, atomic_read(&cache->quiescing_ack));
  79 +}
  80 +
  81 +static void start_quiescing(struct cache *cache)
  82  {
  83         unsigned long flags;
  84
  85         spin_lock_irqsave(&cache->lock, flags);
  86 -       cache->quiescing = 0;
  87 +       cache->quiescing = true;
  88         spin_unlock_irqrestore(&cache->lock, flags);
  89 +
  90 +       wait_for_quiescing_ack(cache);
  91  }
  92
  93 -static bool is_quiescing(struct cache *cache)
  94 +static void stop_quiescing(struct cache *cache)
  95  {
  96 -       int r;
  97         unsigned long flags;
  98
  99         spin_lock_irqsave(&cache->lock, flags);
 100 -       r = cache->quiescing;
 101 +       cache->quiescing = false;
 102         spin_unlock_irqrestore(&cache->lock, flags);
 103
 104 -       return r;
 105 +       atomic_set(&cache->quiescing_ack, 0);
 106  }
 107
 108  static void wait_for_migrations(struct cache *cache)
 109 @@ -1420,16 +1441,15 @@ static void do_worker(struct work_struct
 110         struct cache *cache = container_of(ws, struct cache, worker);
 111
 112         do {
 113 -               if (!is_quiescing(cache))
 114 +               if (!is_quiescing(cache)) {
 115 +                       writeback_some_dirty_blocks(cache);
 116 +                       process_deferred_writethrough_bios(cache);
 117                         process_deferred_bios(cache);
 118 +               }
 119
 120                 process_migrations(cache, &cache->quiesced_migrations, issue_copy);
 121                 process_migrations(cache, &cache->completed_migrations, complete_migration);
 122
 123 -               writeback_some_dirty_blocks(cache);
 124 -
 125 -               process_deferred_writethrough_bios(cache);
 126 -
 127                 if (commit_if_needed(cache)) {
 128                         process_deferred_flush_bios(cache, false);
 129
 130 @@ -1442,6 +1462,9 @@ static void do_worker(struct work_struct
 131                         process_migrations(cache, &cache->need_commit_migrations,
 132                                            migration_success_post_commit);
 133                 }
 134 +
 135 +               ack_quiescing(cache);
 136 +
 137         } while (more_work(cache));
 138  }
 139
 140 @@ -2005,6 +2028,9 @@ static int cache_create(struct cache_arg
 141         atomic_set(&cache->nr_migrations, 0);
 142         init_waitqueue_head(&cache->migration_wait);
 143
 144 +       init_waitqueue_head(&cache->quiescing_wait);
 145 +       atomic_set(&cache->quiescing_ack, 0);
 146 +
 147         r = -ENOMEM;
 148         cache->nr_dirty = 0;
 149         cache->dirty_bitset = alloc_bitset(from_cblock(cache->cache_size));