From: Jens Axboe <axboe@kernel.dk>
To: Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org
Cc: andres@anarazel.de
Subject: Re: [PATCH 2/6] io_uring: add IORING_OP_PROVIDE_BUFFERS
Date: Sat, 29 Feb 2020 10:32:38 -0700 [thread overview]
Message-ID: <f55f74bf-9146-0720-ee8c-021732276d0b@kernel.dk> (raw)
In-Reply-To: <d7eebc93-4efb-730c-21fd-d866dd54eaa6@gmail.com>
On 2/29/20 4:36 AM, Pavel Begunkov wrote:
> On 2/29/2020 7:50 AM, Jens Axboe wrote:
>> On 2/28/20 5:43 PM, Pavel Begunkov wrote:
>>>> +static int io_provide_buffers(struct io_kiocb *req, struct io_kiocb **nxt,
>>>> + bool force_nonblock)
>>>> +{
>>>> + struct io_provide_buf *p = &req->pbuf;
>>>> + struct io_ring_ctx *ctx = req->ctx;
>>>> + struct list_head *list;
>>>> + int ret = 0;
>>>> +
>>>> + /*
>>>> + * "Normal" inline submissions always hold the uring_lock, since we
>>>> + * grab it from the system call. Same is true for the SQPOLL offload.
>>>> + * The only exception is when we've detached the request and issue it
>>>> + * from an async worker thread, grab the lock for that case.
>>>> + */
>>>> + if (!force_nonblock)
>>>> + mutex_lock(&ctx->uring_lock);
>>>
>>> io_poll_task_handler() calls it with force_nonblock==true, but it
>>> doesn't hold the mutex AFAIK.
>>
>> True, that's the only exception. And that command doesn't transfer data
>> so would never need a buffer, but I agree that's perhaps not fully
>> clear. The async task handler grabs the mutex.
>
> Hmm, I meant io_poll_task_func(), which do __io_queue_sqe() for @nxt
> request, which in its turn calls io_issue_sqe(force_nonblock=true).
>
> Does io_poll_task_func() hold @uring_mutex? Otherwise, if @nxt happened
> to be io_provide_buffers(), we get there without holding the mutex and
> with force_nonblock=true.
Ah yes, good point! Not sure why I missed that... I've added the locking
around __io_queue_sqe() if 'nxt' is set in the handler.
--
Jens Axboe
next prev parent reply other threads:[~2020-02-29 17:32 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-28 20:30 [PATCHSET v3] io_uring support for automatic buffers Jens Axboe
2020-02-28 20:30 ` [PATCH 1/6] io_uring: buffer registration infrastructure Jens Axboe
2020-02-28 20:30 ` [PATCH 2/6] io_uring: add IORING_OP_PROVIDE_BUFFERS Jens Axboe
2020-02-29 0:43 ` Pavel Begunkov
2020-02-29 4:50 ` Jens Axboe
2020-02-29 11:36 ` Pavel Begunkov
2020-02-29 17:32 ` Jens Axboe [this message]
2020-02-29 12:08 ` Pavel Begunkov
2020-02-29 17:34 ` Jens Axboe
2020-02-29 18:11 ` Jens Axboe
2020-03-09 17:03 ` Andres Freund
2020-03-09 17:17 ` Jens Axboe
2020-03-09 17:28 ` Andres Freund
2020-03-10 13:33 ` Jens Axboe
2020-02-28 20:30 ` [PATCH 3/6] io_uring: support buffer selection Jens Axboe
2020-02-29 12:21 ` Pavel Begunkov
2020-02-29 17:35 ` Jens Axboe
2020-03-09 17:21 ` Andres Freund
2020-03-10 13:37 ` Jens Axboe
2020-02-28 20:30 ` [PATCH 4/6] io_uring: add IOSQE_BUFFER_SELECT support for IORING_OP_READV Jens Axboe
2020-02-28 20:30 ` [PATCH 5/6] net: abstract out normal and compat msghdr import Jens Axboe
2020-02-28 20:30 ` [PATCH 6/6] io_uring: add IOSQE_BUFFER_SELECT support for IORING_OP_RECVMSG Jens Axboe
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