From: Jens Axboe <axboe@kernel.dk>
To: Lukas Czerner <lczerner@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
jmoyer@redhat.com, akpm@linux-foundation.org
Subject: Re: [PATCH v3] loop: Limit the number of requests in the bio list
Date: Tue, 13 Nov 2012 09:42:58 -0700 [thread overview]
Message-ID: <50A27892.1030800@kernel.dk> (raw)
In-Reply-To: <1352824065-6734-1-git-send-email-lczerner@redhat.com>
> @@ -489,6 +491,12 @@ static void loop_make_request(struct request_queue *q, struct bio *old_bio)
> goto out;
> if (unlikely(rw == WRITE && (lo->lo_flags & LO_FLAGS_READ_ONLY)))
> goto out;
> + if (lo->lo_bio_count >= q->nr_congestion_on) {
> + spin_unlock_irq(&lo->lo_lock);
> + wait_event(lo->lo_req_wait, lo->lo_bio_count <
> + q->nr_congestion_off);
> + spin_lock_irq(&lo->lo_lock);
> + }
This makes me nervous. You are reading lo_bio_count outside the lock. If
you race with the prepare_to_wait() and condition check in
__wait_event(), then you will sleep forever.
md has private helpers for this, seems it would be a good idea to move
these into the regular wait includes and use them here too.
--
Jens Axboe
next prev parent reply other threads:[~2012-11-13 16:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-13 16:27 [PATCH v3] loop: Limit the number of requests in the bio list Lukas Czerner
2012-11-13 16:35 ` Jeff Moyer
2012-11-13 16:42 ` Jens Axboe [this message]
2012-11-14 9:02 ` Lukáš Czerner
2012-11-14 15:21 ` Jens Axboe
2012-11-15 8:20 ` Lukáš Czerner
2012-11-15 14:05 ` Jens Axboe
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