[patch 039/100] dm snapshot: avoid dropping lock in __find_pending_exception

Chris Wright
2009-04-23T07:45:20Z

[-- Attachment #1: dm-snapshot-avoid-dropping-lock-in-__find_pending_exception.patch --]
[-- Type: text/plain, Size: 2442 bytes --]

-stable review patch. If anyone has any objections, please let us know.
---------------------

From: Mikulas Patocka <mpatocka@redhat.com>

upstream commit: c66213921c816f6b1b16a84911618ba9a363b134

It is uncommon and bug-prone to drop a lock in a function that is called with
the lock held, so this is moved to the caller.

Cc: stable@kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
drivers/md/dm-snap.c | 42 ++++++++++++++++++++++++------------------
1 file changed, 24 insertions(+), 18 deletions(-)

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -992,23 +992,10 @@ __lookup_pending_exception(struct dm_sna
* this.
*/
static struct dm_snap_pending_exception *
-__find_pending_exception(struct dm_snapshot *s, struct bio *bio)
+__find_pending_exception(struct dm_snapshot *s,
+ struct dm_snap_pending_exception *pe, chunk_t chunk)
{
- struct dm_snap_pending_exception *pe, *pe2;
- chunk_t chunk = sector_to_chunk(s, bio->bi_sector);
-
- /*
- * Create a new pending exception, we don't want
- * to hold the lock while we do this.
- */
- up_write(&s->lock);
- pe = alloc_pending_exception(s);
- down_write(&s->lock);
-
- if (!s->valid) {
- free_pending_exception(pe);
- return NULL;
- }
+ struct dm_snap_pending_exception *pe2;

pe2 = __lookup_pending_exception(s, chunk);
if (pe2) {
@@ -1083,7 +1070,17 @@ static int snapshot_map(struct dm_target
if (bio_rw(bio) == WRITE) {
pe = __lookup_pending_exception(s, chunk);
if (!pe) {
- pe = __find_pending_exception(s, bio);
+ up_write(&s->lock);
+ pe = alloc_pending_exception(s);
+ down_write(&s->lock);
+
+ if (!s->valid) {
+ free_pending_exception(pe);
+ r = -EIO;
+ goto out_unlock;
+ }
+
+ pe = __find_pending_exception(s, pe, chunk);
if (!pe) {
__invalidate_snapshot(s, -ENOMEM);
r = -EIO;
@@ -1220,7 +1217,16 @@ static int __origin_write(struct list_he

pe = __lookup_pending_exception(snap, chunk);
if (!pe) {
- pe = __find_pending_exception(snap, bio);
+ up_write(&snap->lock);
+ pe = alloc_pending_exception(snap);
+ down_write(&snap->lock);
+
+ if (!snap->valid) {
+ free_pending_exception(pe);
+ goto next_snapshot;
+ }
+
+ pe = __find_pending_exception(snap, pe, chunk);
if (!pe) {
__invalidate_snapshot(snap, -ENOMEM);
goto next_snapshot;