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Date:   Thu, 15 Jul 2021 14:27:58 +0200
From:   Jan Kara <jack@suse.cz>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Naresh Kamboju <naresh.kamboju@linaro.org>,
        Holger Kiehl <Holger.Kiehl@dwd.de>, Jan Kara <jack@suse.cz>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Shuah Khan <shuah@kernel.org>, patches@kernelci.org,
        lkft-triage@lists.linaro.org, Pavel Machek <pavel@denx.de>,
        Jon Hunter <jonathanh@nvidia.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        linux-stable <stable@vger.kernel.org>,
        Paolo Valente <paolo.valente@linaro.org>,
        Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 5.13 000/800] 5.13.2-rc1 review
Message-ID: <20210715122758.GB31920@quack2.suse.cz>
References: <20210712060912.995381202@linuxfoundation.org>
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On Wed 14-07-21 16:26:52, Greg Kroah-Hartman wrote:
> On Wed, Jul 14, 2021 at 07:29:26PM +0530, Naresh Kamboju wrote:
> > On Wed, 14 Jul 2021 at 19:22, Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> > >
> > > On Wed, 14 Jul 2021 at 19:01, Greg Kroah-Hartman
> > > <gregkh@linuxfoundation.org> wrote:
> > > >
> > 
> > <trim>
> > 
> > > My two cents,
> > > While running ssuite long running stress testing we have noticed deadlock.
> > >
> > > > So if you drop that, all works well?  I'll go drop that from the queues
> > > > now.
> > >
> > > Let me drop that patch and test it again.
> > >
> > > Crash log,
> > >
> > > [ 1957.278399] ============================================
> > > [ 1957.283717] WARNING: possible recursive locking detected
> > > [ 1957.289031] 5.13.2-rc1 #1 Not tainted
> > > [ 1957.292703] --------------------------------------------
> > > [ 1957.298016] kworker/u8:7/236 is trying to acquire lock:
> > > [ 1957.303241] ffff8cc203f92c38 (&bfqd->lock){-.-.}-{2:2}, at:
> > > bfq_finish_requeue_request+0x55/0x500 [bfq]
> > > [ 1957.312643]
> > > [ 1957.312643] but task is already holding lock:
> > > [ 1957.318467] ffff8cc203f92c38 (&bfqd->lock){-.-.}-{2:2}, at:
> > > bfq_insert_requests+0x81/0x1750 [bfq]
> > > [ 1957.327334]
> > > [ 1957.327334] other info that might help us debug this:
> > > [ 1957.333852]  Possible unsafe locking scenario:
> > > [ 1957.333852]
> > > [ 1957.339762]        CPU0
> > > [ 1957.342206]        ----
> > > [ 1957.344651]   lock(&bfqd->lock);
> > > [ 1957.347873]   lock(&bfqd->lock);
> > > [ 1957.351097]
> > > [ 1957.351097]  *** DEADLOCK ***
> > > [ 1957.351097]
> > 
> > Also noticed on stable-rc 5.12.17-rc1.
> 
> I dropped the same patch from there as well already, thanks.

OK, when you dropped this patch, please also drop upstream commit
fd2ef39cc9a6b ("blk: Fix lock inversion between ioc lock and bfqd lock").
Because without BFQ patch this block layer patch could cause some
use-after-free issues. I'll have a look if I can understand why BFQ patch
causes problems in stable kernels...

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR