From 149a051f82d2b3860fe32fa182dbc83a66274894 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 29 Jan 2008 22:25:18 +0100 Subject: [PATCH] as-iosched: fix double locking bug in as_merged_requests() If the two requests belong to the same io context, we will attempt to lock the same lock twice. But swapping contexts is pointless in that case, so just check for rioc == nioc before doing the double lock and copy. Tested-by: Olof Johansson Signed-off-by: Jens Axboe --- block/as-iosched.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/block/as-iosched.c b/block/as-iosched.c index b201d16a710..96036846a00 100644 --- a/block/as-iosched.c +++ b/block/as-iosched.c @@ -1275,9 +1275,13 @@ static void as_merged_requests(struct request_queue *q, struct request *req, * Don't copy here but swap, because when anext is * removed below, it must contain the unused context */ - double_spin_lock(&rioc->lock, &nioc->lock, rioc < nioc); - swap_io_context(&rioc, &nioc); - double_spin_unlock(&rioc->lock, &nioc->lock, rioc < nioc); + if (rioc != nioc) { + double_spin_lock(&rioc->lock, &nioc->lock, + rioc < nioc); + swap_io_context(&rioc, &nioc); + double_spin_unlock(&rioc->lock, &nioc->lock, + rioc < nioc); + } } }