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* NVMe induced NULL deref in bt_iter()
@ 2017-06-30 17:26 Jens Axboe
  2017-07-02 10:45 ` Max Gurtovoy
  0 siblings, 1 reply; 15+ messages in thread
From: Jens Axboe @ 2017-06-30 17:26 UTC (permalink / raw)
  To: Max Gurtovoy; +Cc: linux-block@vger.kernel.org

Hi Max,

I remembered you reporting this. I think this is a regression introduced
with the scheduling, since ->rqs[] isn't static anymore. ->static_rqs[]
is, but that's not indexable by the tag we find. So I think we need to
guard those with a NULL check. The actual requests themselves are
static, so we know the memory itself isn't going away. But if we race
with completion, we could find a NULL there, validly.

Since you could reproduce it, can you try the below?

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index d0be72ccb091..b856b2827157 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -214,7 +214,7 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 		bitnr += tags->nr_reserved_tags;
 	rq = tags->rqs[bitnr];
 
-	if (rq->q == hctx->queue)
+	if (rq && rq->q == hctx->queue)
 		iter_data->fn(hctx, rq, iter_data->data, reserved);
 	return true;
 }
@@ -249,8 +249,8 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 	if (!reserved)
 		bitnr += tags->nr_reserved_tags;
 	rq = tags->rqs[bitnr];
-
-	iter_data->fn(rq, iter_data->data, reserved);
+	if (rq)
+		iter_data->fn(rq, iter_data->data, reserved);
 	return true;
 }
 

-- 
Jens Axboe

^ permalink raw reply related	[flat|nested] 15+ messages in thread
end of thread, other threads:[~2017-07-04  9:14 UTC | newest]

Thread overview: 15+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2017-06-30 17:26 NVMe induced NULL deref in bt_iter() Jens Axboe
2017-07-02 10:45 ` Max Gurtovoy
2017-07-02 11:56   ` Sagi Grimberg
2017-07-02 14:37     ` Max Gurtovoy
2017-07-02 15:08       ` Sagi Grimberg
2017-07-03  9:40     ` Ming Lei
2017-07-03 10:07       ` Sagi Grimberg
2017-07-03 12:03         ` Ming Lei
2017-07-03 12:46           ` Max Gurtovoy
2017-07-03 15:54             ` Ming Lei
2017-07-04  6:58               ` Sagi Grimberg
2017-07-04  7:56           ` Sagi Grimberg
2017-07-04  8:08             ` Ming Lei
2017-07-04  9:14               ` Sagi Grimberg
2017-07-03 16:01   ` Jens Axboe

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