From: NeilBrown Date: Mon, 27 Mar 2006 09:18:15 +0000 (-0800) Subject: [PATCH] md: Improve comments about locking situation in raid5 make_request X-Git-Tag: v2.6.17-rc1~283 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=df8e7f7639bab3b2cc536a1d30d5593d65251778;p=linux-2.6 [PATCH] md: Improve comments about locking situation in raid5 make_request Signed-off-by: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index bb16ac231a..8eded08411 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);