dm raid1: clear region outside spinlock

A clear_region function is permitted to block (in practice, rare) but gets
called in rh_update_states() with a spinlock held.

The bits being marked and cleared by the above functions are used
to update the on-disk log, but are never read directly.  We can
perform these operations outside the spinlock since the
bits are only changed within one thread viz.
   - mark_region in rh_inc()
   - clear_region in rh_update_states().

So, we grab the clean_regions list items via list_splice() within the
spinlock and defer clear_region() until we iterate over the list for
deletion - similar to how the recovered_regions list is already handled.
We then move the flush() call down to ensure it encapsulates the changes
which are done by the later calls to clear_region().

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index b3bba98af7728204978c90c99320d692e7626db1..04dce7a66494988ffb9791daae38c16b44f6da75 100644 (file)
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -378,10 +378,8 @@ static void rh_update_states(struct region_hash *rh)
                list_splice(&rh->clean_regions, &clean);
                INIT_LIST_HEAD(&rh->clean_regions);
 
-               list_for_each_entry (reg, &clean, list) {
-                       rh->log->type->clear_region(rh->log, reg->key);
+               list_for_each_entry(reg, &clean, list)
                        list_del(&reg->hash_list);
-               }
        }
 
        if (!list_empty(&rh->recovered_regions)) {
@@ -405,10 +403,12 @@ static void rh_update_states(struct region_hash *rh)
                mempool_free(reg, rh->region_pool);
        }
 
-       rh->log->type->flush(rh->log);
-
-       list_for_each_entry_safe (reg, next, &clean, list)
+       list_for_each_entry_safe(reg, next, &clean, list) {
+               rh->log->type->clear_region(rh->log, reg->key);
                mempool_free(reg, rh->region_pool);
+       }
+
+       rh->log->type->flush(rh->log);
 }
 
 static void rh_inc(struct region_hash *rh, region_t region)