On Mon, 2 Aug 2010 12:29:49 +1000 Neil Brown <neilb@xxxxxxx> wrote: > Ahhhh.... I see the problem. Because a 'generic_make_request' is already > active, the once called by raid10::make_request just queues the request until > the top level one completes. This results in a deadlock. > > I'll have to ponder a bit to figure out the best way to fix this. > So, one good strong cup of tea later I think I have a good solution. Would you be able to test with this patch and confirm that you cannot reproduce the hang? Thanks. NeilBrown diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index 42e64e4..d1d6891 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -825,11 +825,29 @@ static int make_request(mddev_t *mddev, struct bio * bio) */ bp = bio_split(bio, chunk_sects - (bio->bi_sector & (chunk_sects - 1)) ); + + /* Each of these 'make_request' calls will call 'wait_barrier'. + * If the first succeeds but the second blocks due to the resync + * thread raising the barrier, we will deadlock because the + * IO to the underlying device will be queued in generic_make_request + * and will never complete, so will never reduce nr_pending. + * So increment nr_waiting here so no new raise_barriers will + * succeed, and so the second wait_barrier cannot block. + */ + spin_lock_irq(&conf->resync_lock); + conf->nr_waiting++; + spin_unlock_irq(&conf->resync_lock); + if (make_request(mddev, &bp->bio1)) generic_make_request(&bp->bio1); if (make_request(mddev, &bp->bio2)) generic_make_request(&bp->bio2); + spin_lock_irq(&conf->resync_lock); + conf->nr_waiting--; + wake_up(&conf->wait_barrier); + spin_unlock_irq(&conf->resync_lock); + bio_pair_release(bp); return 0; bad_map: -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
