linux-kernel - Re: Lockdep warning on io_file_data_ref

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Message-ID: <13baf2c4-a403-41fc-87ca-6f5cb7999692@kernel.dk>
Date:   Mon, 30 Nov 2020 11:16:48 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Nadav Amit <nadav.amit@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: Lockdep warning on io_file_data_ref_zero() with 5.10-rc5

On 11/28/20 5:13 PM, Pavel Begunkov wrote:
> On 28/11/2020 23:59, Nadav Amit wrote:
>> Hello Pavel,
>>
>> I got the following lockdep splat while rebasing my work on 5.10-rc5 on the
>> kernel (based on 5.10-rc5+).
>>
>> I did not actually confirm that the problem is triggered without my changes,
>> as my iouring workload requires some kernel changes (not iouring changes),
>> yet IMHO it seems pretty clear that this is a result of your commit
>> e297822b20e7f ("io_uring: order refnode recycling”), that acquires a lock in
>> io_file_data_ref_zero() inside a softirq context.
> 
> Yeah, that's true. It was already reported by syzkaller and fixed by Jens, but
> queued for 5.11. Thanks for letting know anyway!
> 
> https://lore.kernel.org/io-uring/948d2d3b-5f36-034d-28e6-7490343a5b59@kernel.dk/T/#t
> 
> 
> Jens, I think it's for the best to add it for 5.10, at least so that lockdep
> doesn't complain.

Yeah maybe, though it's "just" a lockdep issue, it can't trigger any
deadlocks. I'd rather just keep it in 5.11 and ensure it goes to stable.
This isn't new in this series.

-- 
Jens Axboe