From: Jan Kara <firstname.lastname@example.org> To: Ming Lei <email@example.com> Cc: Jan Kara <firstname.lastname@example.org>, Khazhy Kumykov <email@example.com>, Jens Axboe <firstname.lastname@example.org>, email@example.com, Paolo Valente <firstname.lastname@example.org> Subject: Re: [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Date: Fri, 21 May 2021 15:47:13 +0200 [thread overview] Message-ID: <20210521134713.GO18952@quack2.suse.cz> (raw) In-Reply-To: <YKe3RXOjaw4Lm2dL@T590> On Fri 21-05-21 21:36:05, Ming Lei wrote: > On Fri, May 21, 2021 at 02:05:51PM +0200, Jan Kara wrote: > > On Fri 21-05-21 14:54:09, Ming Lei wrote: > > > On Thu, May 20, 2021 at 08:29:49PM -0700, Khazhy Kumykov wrote: > > > > On Thu, May 20, 2021 at 5:57 PM Ming Lei <email@example.com> wrote: > > > > > > > > > > On Fri, May 21, 2021 at 12:33:53AM +0200, Jan Kara wrote: > > > > > > Lockdep complains about lock inversion between ioc->lock and bfqd->lock: > > > > > > > > > > > > bfqd -> ioc: > > > > > > put_io_context+0x33/0x90 -> ioc->lock grabbed > > > > > > blk_mq_free_request+0x51/0x140 > > > > > > blk_put_request+0xe/0x10 > > > > > > blk_attempt_req_merge+0x1d/0x30 > > > > > > elv_attempt_insert_merge+0x56/0xa0 > > > > > > blk_mq_sched_try_insert_merge+0x4b/0x60 > > > > > > bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed > > > > > > > > > > We could move blk_put_request() into scheduler code, then the lock > > > > > inversion is avoided. So far only mq-deadline and bfq calls into > > > > > blk_mq_sched_try_insert_merge(), and this change should be small. > > > > > > > > We'd potentially be putting multiple requests if we keep the recursive merge. > > > > > > Oh, we still can pass a list to hold all requests to be freed, then free > > > them all outside in scheduler code. > > > > If we cannot really get rid of the recursive merge (not yet convinced), > > this is also an option I've considered. I was afraid what can we use in > > struct request to attach request to a list but it seems .merged_requests > > handlers remove the request from the queuelist already so we should be fine > > using that. > > The request has been removed from scheduler queue, and safe to free, > so it is safe to be held in one temporary list. Not quite, there's still ->finish_request hook that will be called from blk_mq_free_request() on the request and e.g. BFQ performs quite a lot of cleanup there. But yes, at least queuelist seems to be available for reuse here. Honza -- Jan Kara <firstname.lastname@example.org> SUSE Labs, CR
next prev parent reply other threads:[~2021-05-21 13:47 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-20 22:33 [PATCH 0/2] block: Fix deadlock when merging requests with BFQ Jan Kara 2021-05-20 22:33 ` [PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge() Jan Kara 2021-05-21 0:42 ` Ming Lei 2021-05-21 11:53 ` Jan Kara 2021-05-21 13:12 ` Ming Lei 2021-05-21 13:44 ` Jan Kara 2021-05-20 22:33 ` [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Jan Kara 2021-05-21 0:57 ` Ming Lei 2021-05-21 3:29 ` Khazhy Kumykov 2021-05-21 6:54 ` Ming Lei 2021-05-21 12:05 ` Jan Kara 2021-05-21 13:36 ` Ming Lei 2021-05-21 13:47 ` Jan Kara [this message] 2021-05-24 10:04 [PATCH 0/2 v2] block: Fix deadlock when merging requests with BFQ Jan Kara 2021-05-24 10:04 ` [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Jan Kara 2021-05-25 0:29 ` Ming Lei 2021-05-28 9:33 ` Paolo Valente 2021-05-28 12:30 [PATCH 0/2 v3] block: Fix deadlock when merging requests with BFQ Jan Kara 2021-05-28 12:30 ` [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Jan Kara 2021-06-23 9:36 [PATCH 0/2 v4] block: Fix deadlock when merging requests with BFQ Jan Kara 2021-06-23 9:36 ` [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Jan Kara
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