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Message-ID: <827b11ed-2fb3-40ae-a266-17080fa751be@kernel.dk>
Date: Tue, 1 Apr 2025 12:14:28 -0600
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Subject: Re: [PATCH 1/1] io_uring: add lockdep checks for io_handle_tw_list
To: Pavel Begunkov <asml.silence@gmail.com>, 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: Jens Axboe <axboe@kernel.dk>
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On 4/1/25 11:19 AM, Pavel Begunkov wrote:
> 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).
Yep let's do that, but it'd still be nice to dump what func is if it
ends up triggering.
--
Jens Axboe