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Date: Mon, 18 Mar 2024 12:46:25 +0000
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Subject: Re: [PATCH v2 03/14] io_uring/cmd: make io_uring_cmd_done irq safe
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To: Ming Lei <ming.lei@redhat.com>
Cc: io-uring@vger.kernel.org, linux-block@vger.kernel.org,
Jens Axboe <axboe@kernel.dk>, Kanchan Joshi <joshi.k@samsung.com>
References: <cover.1710720150.git.asml.silence@gmail.com>
<faeec0d1e7c740a582f51f80626f61c745ed9a52.1710720150.git.asml.silence@gmail.com>
<Zff25z0fPGBPfJs1@fedora> <4c6a5b55-2833-4ef7-a514-577fe61160dd@gmail.com>
<Zfgsk8mND0cah3DP@fedora>
From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <Zfgsk8mND0cah3DP@fedora>
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On 3/18/24 11:59, Ming Lei wrote:
> On Mon, Mar 18, 2024 at 11:50:32AM +0000, Pavel Begunkov wrote:
>> On 3/18/24 08:10, Ming Lei wrote:
>>> On Mon, Mar 18, 2024 at 12:41:48AM +0000, Pavel Begunkov wrote:
>>>> io_uring_cmd_done() is called from the irq context and is considered to
>>>> be irq safe, however that's not the case if the driver requires
>>>> cancellations because io_uring_cmd_del_cancelable() could try to take
>>>> the uring_lock mutex.
>>>>
>>>> Clean up the confusion, by deferring cancellation handling to
>>>> locked task_work if we came into io_uring_cmd_done() from iowq
>>>> or other IO_URING_F_UNLOCKED path.
>>>>
>>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>>> ---
>>>> io_uring/uring_cmd.c | 24 +++++++++++++++++-------
>>>> 1 file changed, 17 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
>>>> index ec38a8d4836d..9590081feb2d 100644
>>>> --- a/io_uring/uring_cmd.c
>>>> +++ b/io_uring/uring_cmd.c
>>>> @@ -14,19 +14,18 @@
>>>> #include "rsrc.h"on #include "uring_cmd.h"
>>>> -static void io_uring_cmd_del_cancelable(struct io_uring_cmd *cmd,
>>>> - unsigned int issue_flags)
>>>> +static void io_uring_cmd_del_cancelable(struct io_uring_cmd *cmd)
>>>> {
>>>> struct io_kiocb *req = cmd_to_io_kiocb(cmd);
>>>> struct io_ring_ctx *ctx = req->ctx;
>>>> + lockdep_assert_held(&ctx->uring_lock);
>>>> +
>>>> if (!(cmd->flags & IORING_URING_CMD_CANCELABLE))
>>>> return;
>>>> cmd->flags &= ~IORING_URING_CMD_CANCELABLE;
>>>> - io_ring_submit_lock(ctx, issue_flags);
>>>> hlist_del(&req->hash_node);
>>>> - io_ring_submit_unlock(ctx, issue_flags);
>>>> }
>>>> /*
>>>> @@ -44,6 +43,9 @@ void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
>>>> struct io_kiocb *req = cmd_to_io_kiocb(cmd);
>>>> struct io_ring_ctx *ctx = req->ctx;
>>>> + if (WARN_ON_ONCE(ctx->flags & IORING_SETUP_IOPOLL))
>>>> + return;
>>>> +
>>>
>>> This way limits cancelable command can't be used in iopoll context, and
>>> it isn't reasonable, and supporting iopoll has been in ublk todo list,
>>> especially single ring context is shared for both command and normal IO.
>>
>> That's something that can be solved when it's needed, and hence the
>> warning so it's not missed. That would need del_cancelable on the
>> ->iopoll side, but depends on the "leaving in cancel queue"
>> problem resolution.
>
> The current code is actually working with iopoll, so adding the warning
> can be one regression. Maybe someone has been using ublk with iopoll.
Hmm, I don't see ->uring_cmd_iopoll implemented anywhere, and w/o
it io_uring should fail the request:
int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
{
...
if (ctx->flags & IORING_SETUP_IOPOLL) {
if (!file->f_op->uring_cmd_iopoll)
return -EOPNOTSUPP;
issue_flags |= IO_URING_F_IOPOLL;
}
}
Did I miss it somewhere?
--
Pavel Begunkov