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authorNeilBrown <neilb@suse.de>2006-03-27 01:18:15 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-27 08:45:02 -0800
commitdf8e7f7639bab3b2cc536a1d30d5593d65251778 (patch)
tree93eb1e93e5f6e0f27f85b8b5d925c2dad2929c2e /drivers
parente464eafdb4400c6d6576ba3840d8bd40340f8a96 (diff)
[PATCH] md: Improve comments about locking situation in raid5 make_request
Signed-off-by: Neil Brown <neilb@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/md/raid5.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bb16ac231a4..8eded08411f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1768,6 +1768,14 @@ static int make_request(request_queue_t *q, struct bio * bi)
if (likely(conf->expand_progress == MaxSector))
disks = conf->raid_disks;
else {
+ /* spinlock is needed as expand_progress may be
+ * 64bit on a 32bit platform, and so it might be
+ * possible to see a half-updated value
+ * Ofcourse expand_progress could change after
+ * the lock is dropped, so once we get a reference
+ * to the stripe that we think it is, we will have
+ * to check again.
+ */
spin_lock_irq(&conf->device_lock);
disks = conf->raid_disks;
if (logical_sector >= conf->expand_progress)
@@ -1791,7 +1799,12 @@ static int make_request(request_queue_t *q, struct bio * bi)
if (sh) {
if (unlikely(conf->expand_progress != MaxSector)) {
/* expansion might have moved on while waiting for a
- * stripe, so we much do the range check again.
+ * stripe, so we must do the range check again.
+ * Expansion could still move past after this
+ * test, but as we are holding a reference to
+ * 'sh', we know that if that happens,
+ * STRIPE_EXPANDING will get set and the expansion
+ * won't proceed until we finish with the stripe.
*/
int must_retry = 0;
spin_lock_irq(&conf->device_lock);