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author | Joe Thornber <ejt@redhat.com> | 2014-04-08 10:29:01 (GMT) |
---|---|---|
committer | Mike Snitzer <snitzer@redhat.com> | 2014-04-08 14:18:35 (GMT) |
commit | b10ebd34cccae1b431caf1be54919aede2be7cbe (patch) | |
tree | f8f848169991555d7ea0719740da37645e405c99 /drivers/md | |
parent | 5e3283e2920a0bd8a806964d80274b8756e0dd7f (diff) | |
download | linux-b10ebd34cccae1b431caf1be54919aede2be7cbe.tar.xz |
dm thin: fix rcu_read_lock being held in code that can sleep
Commit c140e1c4e23 ("dm thin: use per thin device deferred bio lists")
introduced the use of an rculist for all active thin devices. The use
of rcu_read_lock() in process_deferred_bios() can result in a BUG if a
dm_bio_prison_cell must be allocated as a side-effect of bio_detain():
BUG: sleeping function called from invalid context at mm/mempool.c:203
in_atomic(): 1, irqs_disabled(): 0, pid: 6, name: kworker/u8:0
3 locks held by kworker/u8:0/6:
#0: ("dm-" "thin"){.+.+..}, at: [<ffffffff8106be42>] process_one_work+0x192/0x550
#1: ((&pool->worker)){+.+...}, at: [<ffffffff8106be42>] process_one_work+0x192/0x550
#2: (rcu_read_lock){.+.+..}, at: [<ffffffff816360b5>] do_worker+0x5/0x4d0
We can't process deferred bios with the rcu lock held, since
dm_bio_prison_cell allocation may block if the bio-prison's cell mempool
is exhausted.
To fix:
- Introduce a refcount and completion field to each thin_c
- Add thin_get/put methods for adjusting the refcount. If the refcount
hits zero then the completion is triggered.
- Initialise refcount to 1 when creating thin_c
- When iterating the active_thins list we thin_get() whilst the rcu
lock is held.
- After the rcu lock is dropped we process the deferred bios for that
thin.
- When destroying a thin_c we thin_put() and then wait for the
completion -- to avoid a race between the worker thread iterating
from that thin_c and destroying the thin_c.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
-rw-r--r-- | drivers/md/dm-thin.c | 70 |
1 files changed, 67 insertions, 3 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c index ae5fd0b..28fc282 100644 --- a/drivers/md/dm-thin.c +++ b/drivers/md/dm-thin.c @@ -232,6 +232,13 @@ struct thin_c { struct bio_list deferred_bio_list; struct bio_list retry_on_resume_list; struct rb_root sort_bio_list; /* sorted list of deferred bios */ + + /* + * Ensures the thin is not destroyed until the worker has finished + * iterating the active_thins list. + */ + atomic_t refcount; + struct completion can_destroy; }; /*----------------------------------------------------------------*/ @@ -1486,6 +1493,45 @@ static void process_thin_deferred_bios(struct thin_c *tc) blk_finish_plug(&plug); } +static void thin_get(struct thin_c *tc); +static void thin_put(struct thin_c *tc); + +/* + * We can't hold rcu_read_lock() around code that can block. So we + * find a thin with the rcu lock held; bump a refcount; then drop + * the lock. + */ +static struct thin_c *get_first_thin(struct pool *pool) +{ + struct thin_c *tc = NULL; + + rcu_read_lock(); + if (!list_empty(&pool->active_thins)) { + tc = list_entry_rcu(pool->active_thins.next, struct thin_c, list); + thin_get(tc); + } + rcu_read_unlock(); + + return tc; +} + +static struct thin_c *get_next_thin(struct pool *pool, struct thin_c *tc) +{ + struct thin_c *old_tc = tc; + + rcu_read_lock(); + list_for_each_entry_continue_rcu(tc, &pool->active_thins, list) { + thin_get(tc); + thin_put(old_tc); + rcu_read_unlock(); + return tc; + } + thin_put(old_tc); + rcu_read_unlock(); + + return NULL; +} + static void process_deferred_bios(struct pool *pool) { unsigned long flags; @@ -1493,10 +1539,11 @@ static void process_deferred_bios(struct pool *pool) struct bio_list bios; struct thin_c *tc; - rcu_read_lock(); - list_for_each_entry_rcu(tc, &pool->active_thins, list) + tc = get_first_thin(pool); + while (tc) { process_thin_deferred_bios(tc); - rcu_read_unlock(); + tc = get_next_thin(pool, tc); + } /* * If there are any deferred flush bios, we must commit @@ -3061,11 +3108,25 @@ static struct target_type pool_target = { /*---------------------------------------------------------------- * Thin target methods *--------------------------------------------------------------*/ +static void thin_get(struct thin_c *tc) +{ + atomic_inc(&tc->refcount); +} + +static void thin_put(struct thin_c *tc) +{ + if (atomic_dec_and_test(&tc->refcount)) + complete(&tc->can_destroy); +} + static void thin_dtr(struct dm_target *ti) { struct thin_c *tc = ti->private; unsigned long flags; + thin_put(tc); + wait_for_completion(&tc->can_destroy); + spin_lock_irqsave(&tc->pool->lock, flags); list_del_rcu(&tc->list); spin_unlock_irqrestore(&tc->pool->lock, flags); @@ -3192,6 +3253,9 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv) mutex_unlock(&dm_thin_pool_table.mutex); + atomic_set(&tc->refcount, 1); + init_completion(&tc->can_destroy); + spin_lock_irqsave(&tc->pool->lock, flags); list_add_tail_rcu(&tc->list, &tc->pool->active_thins); spin_unlock_irqrestore(&tc->pool->lock, flags); |