From: Jens Axboe <axboe@kernel.dk>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: linux-block@vger.kernel.org, Gabriel C <nix.or.die@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [BUG] Potential deadlock in the block layer
Date: Mon, 13 Feb 2017 08:02:12 -0700 [thread overview]
Message-ID: <4d3f25fc-7480-769c-2f4f-e5271a47f7c3@kernel.dk> (raw)
In-Reply-To: <alpine.DEB.2.20.1702131505580.3619@nanos>
On 02/13/2017 07:14 AM, Thomas Gleixner wrote:
> Gabriel reported the lockdep splat below while investigating something
> different.
>
> Explanation for the splat is in the function comment above
> del_timer_sync().
>
> I can reproduce it as well and it's clearly broken.
Agree, the disable logic is broken. The below isn't super pretty, but it
should do the trick for 4.10.
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index c73a6fcaeb9d..838f07e2b64a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3758,7 +3758,7 @@ static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
}
#ifdef CONFIG_CFQ_GROUP_IOSCHED
-static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
+static bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
{
struct cfq_data *cfqd = cic_to_cfqd(cic);
struct cfq_queue *cfqq;
@@ -3775,15 +3775,7 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
* spuriously on a newly created cic but there's no harm.
*/
if (unlikely(!cfqd) || likely(cic->blkcg_serial_nr == serial_nr))
- return;
-
- /*
- * If we have a non-root cgroup, we can depend on that to
- * do proper throttling of writes. Turn off wbt for that
- * case, if it was enabled by default.
- */
- if (nonroot_cg)
- wbt_disable_default(cfqd->queue);
+ return nonroot_cg;
/*
* Drop reference to queues. New queues will be assigned in new
@@ -3804,9 +3796,13 @@ static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
}
cic->blkcg_serial_nr = serial_nr;
+ return nonroot_cg;
}
#else
-static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
+static inline bool check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
+{
+ return false;
+}
#endif /* CONFIG_CFQ_GROUP_IOSCHED */
static struct cfq_queue **
@@ -4448,11 +4444,12 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
const int rw = rq_data_dir(rq);
const bool is_sync = rq_is_sync(rq);
struct cfq_queue *cfqq;
+ bool disable_wbt;
spin_lock_irq(q->queue_lock);
check_ioprio_changed(cic, bio);
- check_blkcg_changed(cic, bio);
+ disable_wbt = check_blkcg_changed(cic, bio);
new_queue:
cfqq = cic_to_cfqq(cic, is_sync);
if (!cfqq || cfqq == &cfqd->oom_cfqq) {
@@ -4488,6 +4485,10 @@ cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
rq->elv.priv[0] = cfqq;
rq->elv.priv[1] = cfqq->cfqg;
spin_unlock_irq(q->queue_lock);
+
+ if (disable_wbt)
+ wbt_disable_default(q);
+
return 0;
}
--
Jens Axboe
next prev parent reply other threads:[~2017-02-13 15:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-13 14:14 [BUG] Potential deadlock in the block layer Thomas Gleixner
2017-02-13 15:02 ` Jens Axboe [this message]
2017-02-16 14:35 ` Thomas Gleixner
2017-02-16 14:56 ` Jens Axboe
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