[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <965a473d-596a-4cf4-8ec2-a8626c4c73f6@gmail.com>
Date: Mon, 4 Nov 2024 15:27:27 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: Jens Axboe <axboe@...nel.dk>,
syzbot <syzbot+e333341d3d985e5173b2@...kaller.appspotmail.com>,
io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [io-uring?] [usb?] WARNING in io_get_cqe_overflow (2)
On 11/4/24 15:08, Jens Axboe wrote:
> On 11/4/24 6:13 AM, Pavel Begunkov wrote:
>> On 11/4/24 11:31, syzbot wrote:
>>> syzbot has bisected this issue to:
>>>
>>> commit 3f1a546444738b21a8c312a4b49dc168b65c8706
>>> Author: Jens Axboe <axboe@...nel.dk>
>>> Date: Sat Oct 26 01:27:39 2024 +0000
>>>
>>> io_uring/rsrc: get rid of per-ring io_rsrc_node list
>>>
>>> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15aaa1f7980000
>>> start commit: c88416ba074a Add linux-next specific files for 20241101
>>> git tree: linux-next
>>> final oops: https://syzkaller.appspot.com/x/report.txt?x=17aaa1f7980000
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13aaa1f7980000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=704b6be2ac2f205f
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=e333341d3d985e5173b2
>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16ec06a7980000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12c04740580000
>>>
>>> Reported-by: syzbot+e333341d3d985e5173b2@...kaller.appspotmail.com
>>> Fixes: 3f1a54644473 ("io_uring/rsrc: get rid of per-ring io_rsrc_node list")
>>>
>>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
>>
>> Previously all puts were done by requests, which in case of an exiting
>> ring were fallback'ed to normal tw. Now, the unregister path posts CQEs,
>> while the original task is still alive. Should be fine in general because
>> at this point there could be no requests posting in parallel and all
>> is synchronised, so it's a false positive, but we need to change the assert
>> or something else.
>
> Maybe something ala the below? Also changes these triggers to be
> _once(), no point spamming them.
>
> diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
> index 00409505bf07..7792ed91469b 100644
> --- a/io_uring/io_uring.h
> +++ b/io_uring/io_uring.h
> @@ -137,10 +137,11 @@ static inline void io_lockdep_assert_cq_locked(struct io_ring_ctx *ctx)
> * Not from an SQE, as those cannot be submitted, but via
> * updating tagged resources.
> */
> - if (ctx->submitter_task->flags & PF_EXITING)
> - lockdep_assert(current_work());
> + if (ctx->submitter_task->flags & PF_EXITING ||
> + percpu_ref_is_dying(&ctx->refs))
io_move_task_work_from_local() executes requests with a normal
task_work of a possible alive task, which which will the check.
I was thinking to kill the extra step as it doesn't make sense,
git garbage digging shows the patch below, but I don't remember
if it has ever been tested.
commit 65560732da185c85f472e9c94e6b8ff147fc4b96
Author: Pavel Begunkov <asml.silence@...il.com>
Date: Fri Jun 7 13:13:06 2024 +0100
io_uring: skip normal tw with DEFER_TASKRUN
DEFER_TASKRUN execution first falls back to normal task_work and only
then, when the task is dying, to workers. It's cleaner to remove the
middle step and use workers as the only fallback. It also detaches
DEFER_TASKRUN and normal task_work handling from each other.
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 9789cf8c68c1..d9e3661ff93d 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1111,9 +1111,8 @@ static inline struct llist_node *io_llist_xchg(struct llist_head *head,
return xchg(&head->first, new);
}
-static __cold void io_fallback_tw(struct io_uring_task *tctx, bool sync)
+static __cold void __io_fallback_tw(struct llist_node *node, bool sync)
{
- struct llist_node *node = llist_del_all(&tctx->task_list);
struct io_ring_ctx *last_ctx = NULL;
struct io_kiocb *req;
@@ -1139,6 +1138,13 @@ static __cold void io_fallback_tw(struct io_uring_task *tctx, bool sync)
}
}
+static __cold void io_fallback_tw(struct io_uring_task *tctx, bool sync)
+{
+ struct llist_node *node = llist_del_all(&tctx->task_list);
+
+ __io_fallback_tw(node, sync);
+}
+
struct llist_node *tctx_task_work_run(struct io_uring_task *tctx,
unsigned int max_entries,
unsigned int *count)
@@ -1287,13 +1293,7 @@ static void __cold io_move_task_work_from_local(struct io_ring_ctx *ctx)
struct llist_node *node;
node = llist_del_all(&ctx->work_llist);
- while (node) {
- struct io_kiocb *req = container_of(node, struct io_kiocb,
- io_task_work.node);
-
- node = node->next;
- io_req_normal_work_add(req);
- }
+ __io_fallback_tw(node, false);
}
static bool io_run_local_work_continue(struct io_ring_ctx *ctx, int events,
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index e46d13e8a215..bc0a800b5ae7 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -128,7 +128,7 @@ static inline void io_lockdep_assert_cq_locked(struct io_ring_ctx *ctx)
* Not from an SQE, as those cannot be submitted, but via
* updating tagged resources.
*/
- if (ctx->submitter_task->flags & PF_EXITING)
+ if (percpu_ref_is_dying(&ctx->refs))
lockdep_assert(current_work());
else
lockdep_assert(current == ctx->submitter_task);
--
Pavel Begunkov
Powered by blists - more mailing lists