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Subject: Re: [PATCH 1/1] io_uring: add lockdep checks for io_handle_tw_list
To: Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org
References: <ffd30102aee729e48911f595d1c05804e59b0403.1743522348.git.asml.silence@gmail.com>
<65765d68-cda0-41fb-acdf-58e7b5c1243f@kernel.dk>
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From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <65765d68-cda0-41fb-acdf-58e7b5c1243f@kernel.dk>
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On 4/1/25 17:13, Jens Axboe wrote:
> On 4/1/25 9:46 AM, Pavel Begunkov wrote:
>> Add a lockdep check to io_handle_tw_list() verifying that the context is
>> locked and no task work drops it by accident.
>
> I think we'd want a bit more of a "why" explanation here, but I can add
> that while committing.
>
>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>> index 6df996d01ccf..13e0b48d1aac 100644
>> --- a/io_uring/io_uring.c
>> +++ b/io_uring/io_uring.c
>> @@ -1054,6 +1054,10 @@ struct llist_node *io_handle_tw_list(struct llist_node *node,
>> mutex_lock(&ctx->uring_lock);
>> percpu_ref_get(&ctx->refs);
>> }
>> +
>> + lockdep_assert(req->ctx == ctx);
>> + lockdep_assert_held(&ctx->uring_lock);
>> +
>> INDIRECT_CALL_2(req->io_task_work.func,
>> io_poll_task_func, io_req_rw_complete,
>> req, ts);
>
> If the assumption is that some previous tw messed things up, might not
> be a bad idea to include dumping of that if one of the above lockdep
> asserts fail? Preferably in such a way that code generation is the same
> when lockdep isn't set...
We can move it after the tw run where it still has the request
(but doesn't own it).
--
Pavel Begunkov