From: Hao Xu <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Cc: Pavel Begunkov <[email protected]>
Subject: Re: [PATCH 2/2] io_uring: kbuf: add comments for some tricky code
Date: Fri, 17 Jun 2022 11:59:09 +0800 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 6/17/22 04:37, Jens Axboe wrote:
> On 6/14/22 6:01 AM, Hao Xu wrote:
>> From: Hao Xu <[email protected]>
>>
>> Add comments to explain why it is always under uring lock when
>> incrementing head in __io_kbuf_recycle. And rectify one comemnt about
>> kbuf consuming in iowq case.
>
> Was there a 1/2 patch in this series? This one has a subject of 2/2...
Apologize for this, 1/2 and this should be separate, and I'm not going
to send 1/2 for now for some reason. I should have change the subject.
>
>> Signed-off-by: Hao Xu <[email protected]>
>> ---
>> io_uring/kbuf.c | 20 ++++++++++++++------
>> 1 file changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
>> index 9cdbc018fd64..37f06456bf30 100644
>> --- a/io_uring/kbuf.c
>> +++ b/io_uring/kbuf.c
>> @@ -50,6 +50,13 @@ void __io_kbuf_recycle(struct io_kiocb *req, unsigned issue_flags)
>> if (req->flags & REQ_F_BUFFER_RING) {
>> if (req->buf_list) {
>> if (req->flags & REQ_F_PARTIAL_IO) {
>> + /*
>> + * if we reach here, uring_lock has been
>> + ?* holden. Because in iowq, we already
>> + ?* cleared req->buf_list to NULL when got
>> + ?* the buffer from the ring, which means
>> + ?* we cannot be here in that case.
>> + */
>
> There's a weird character before the '*' in most lines? I'd rephrase the
> above as:
>
> If we end up here, then the io_uring_lock has been kept held since we
> retrieved the buffer. For the io-wq case, we already cleared
> req->buf_list when the buffer was retrieved, hence it cannot be set
> here for that case.
>
> And make sure it lines up around 80 chars, your lines look very short.
I'll do the change, as well as figuring out the weird char stuff.
Thanks.
>
>> @@ -128,12 +135,13 @@ static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
>> if (issue_flags & IO_URING_F_UNLOCKED) {
>> /*
>> * If we came in unlocked, we have no choice but to consume the
>> - * buffer here. This does mean it'll be pinned until the IO
>> - * completes. But coming in unlocked means we're in io-wq
>> - * context, hence there should be no further retry. For the
>> - * locked case, the caller must ensure to call the commit when
>> - * the transfer completes (or if we get -EAGAIN and must poll
>> - * or retry).
>> + * buffer here otherwise nothing ensures the buffer not being
>> + * used by others. This does mean it'll be pinned until the IO
>> + * completes though coming in unlocked means we're in io-wq
>> + * context and there may be further retries in async hybrid mode.
>> + * For the locked case, the caller must ensure to call the commit
>> + * when the transfer completes (or if we get -EAGAIN and must
>> + * poll or retry).
>
> and similarly:
>
> buffer here, otherwise nothing ensures that the buffer won't get used by
> others. This does mean it'll be pinned until the IO completes, coming in
> unlocked means we're being called from io-wq context and there may be
> further retries in async hybrid mode. For the locked case, the caller
> must call commit when the transfer completes (or if we get -EAGAIN and
> must poll of retry).
>
Gotcha.
prev parent reply other threads:[~2022-06-17 3:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-14 12:01 [PATCH 2/2] io_uring: kbuf: add comments for some tricky code Hao Xu
2022-06-16 4:19 ` Hao Xu
2022-06-16 20:37 ` Jens Axboe
2022-06-17 3:59 ` Hao Xu [this message]
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