Messages in this thread Patch in this message | | | From | Ming Lei <> | Subject | [PATCH] sbitmap: Protect swap_lock from hardirq | Date | Tue, 15 Jan 2019 11:59:52 +0800 |
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The original report is actually one real deadlock:
[ 106.132865] Possible interrupt unsafe locking scenario: [ 106.132865] [ 106.133659] CPU0 CPU1 [ 106.134194] ---- ---- [ 106.134733] lock(&(&sb->map[i].swap_lock)->rlock); [ 106.135318] local_irq_disable(); [ 106.136014] lock(&sbq->ws[i].wait); [ 106.136747] lock(&(&hctx->dispatch_wait_lock)->rlock); [ 106.137742] <Interrupt> [ 106.138110] lock(&sbq->ws[i].wait);
Because we may call blk_mq_get_driver_tag() directly from blk_mq_dispatch_rq_list() without holding any lock, then HARDIRQ may come and the above DEADLOCK is triggered.
ab53dcfb3e7b ("sbitmap: Protect swap_lock from hardirq") tries to fix this issue by using 'spin_lock_bh', which isn't enough because we complete request from hardirq context direclty in case of multiqueue.
Cc: Clark Williams <williams@redhat.com> Fixes: ab53dcfb3e7b ("sbitmap: Protect swap_lock from hardirq") Cc: Jens Axboe <axboe@kernel.dk> Cc: Ming Lei <ming.lei@redhat.com> Cc: Guenter Roeck <linux@roeck-us.net> Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ming Lei <ming.lei@redhat.com> --- lib/sbitmap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 864354000e04..5b382c1244ed 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -27,8 +27,9 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index) { unsigned long mask, val; bool ret = false; + unsigned long flags; - spin_lock_bh(&sb->map[index].swap_lock); + spin_lock_irqsave(&sb->map[index].swap_lock, flags); if (!sb->map[index].cleared) goto out_unlock; @@ -49,7 +50,7 @@ static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index) ret = true; out_unlock: - spin_unlock_bh(&sb->map[index].swap_lock); + spin_unlock_irqrestore(&sb->map[index].swap_lock, flags); return ret; } -- 2.14.4
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