Messages in this thread Patch in this message | | | Subject | [PATCH v2] drivers/md: use proper rcu accessor | From | Eric Dumazet <> | Date | Sun, 23 Nov 2014 09:34:29 -0800 |
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From: Eric Dumazet <edumazet@google.com>
rcu_dereference() should be used in sections protected by rcu_read_lock.
For writers, holding some kind of mutex or lock, rcu_dereference_protected() is the way to go, adding explicit lockdep bits.
In __unbind(), we are the last user of this mapped device, so can use the constant '1' instead of a lockdep_is_held(), not consistent with other uses of rcu_dereference_protected() which use md->suspend_lock mutex.
Reported-by: Kirill A. Shutemov <kirill@shutemov.name> Signed-off-by: Eric Dumazet <edumazet@google.com> Fixes: 33423974bfc1 ("dm: Use rcu_dereference() for accessing rcu pointer") Cc: Pranith Kumar <bobby.prani@gmail.com> Cc: Mike Snitzer <snitzer@redhat.com> ---
v2: changed all buggy rcu_dereference() BTW, having a mutex named suspend_lock is ugly, IMO.
drivers/md/dm.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index a0ece87ad426..5919d933bce9 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -2335,7 +2335,8 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t, merge_is_optional = dm_table_merge_is_optional(t); - old_map = rcu_dereference(md->map); + old_map = rcu_dereference_protected(md->map, + lockdep_is_held(&md->suspend_lock)); rcu_assign_pointer(md->map, t); md->immutable_target_type = dm_table_get_immutable_target_type(t); @@ -2355,7 +2356,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t, */ static struct dm_table *__unbind(struct mapped_device *md) { - struct dm_table *map = rcu_dereference(md->map); + struct dm_table *map = rcu_dereference_protected(md->map, 1); if (!map) return NULL; @@ -2850,7 +2851,8 @@ retry: goto retry; } - map = rcu_dereference(md->map); + map = rcu_dereference_protected(md->map, + lockdep_is_held(&md->suspend_lock)); r = __dm_suspend(md, map, suspend_flags, TASK_INTERRUPTIBLE); if (r) @@ -2908,7 +2910,8 @@ retry: goto retry; } - map = rcu_dereference(md->map); + map = rcu_dereference_protected(md->map, + lockdep_is_held(&md->suspend_lock)); if (!map || !dm_table_get_size(map)) goto out; @@ -2943,7 +2946,8 @@ static void __dm_internal_suspend(struct mapped_device *md, unsigned suspend_fla return; /* nest suspend */ } - map = rcu_dereference(md->map); + map = rcu_dereference_protected(md->map, + lockdep_is_held(&md->suspend_lock)); /* * Using TASK_UNINTERRUPTIBLE because only NOFLUSH internal suspend is
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