From: Xiaoguang Wang <[email protected]>
To: Jens Axboe <[email protected]>, [email protected]
Cc: [email protected]
Subject: Re: [PATCH 2/2] io_uring: add memory barrier to synchronize io_kiocb's result and iopoll_completed
Date: Mon, 15 Jun 2020 23:32:31 +0800 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
hi,
> On 6/15/20 8:48 AM, Xiaoguang Wang wrote:
>> hi,
>>
>>> On 6/15/20 3:24 AM, Xiaoguang Wang wrote:
>>>> In io_complete_rw_iopoll(), stores to io_kiocb's result and iopoll
>>>> completed are two independent store operations, to ensure that once
>>>> iopoll_completed is ture and then req->result must been perceived by
>>>> the cpu executing io_do_iopoll(), proper memory barrier should be used.
>>>>
>>>> And in io_do_iopoll(), we check whether req->result is EAGAIN, if it is,
>>>> we'll need to issue this io request using io-wq again. In order to just
>>>> issue a single smp_rmb() on the completion side, move the re-submit work
>>>> to io_iopoll_complete().
>>>
>>> Did you actually test this one?
>> I only run test cases in liburing/test in a vm.
>>
>>>
>>>> @@ -1736,11 +1748,20 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
>>>> {
>>>> struct req_batch rb;
>>>> struct io_kiocb *req;
>>>> + LIST_HEAD(again);
>>>> +
>>>> + /* order with ->result store in io_complete_rw_iopoll() */
>>>> + smp_rmb();
>>>>
>>>> rb.to_free = rb.need_iter = 0;
>>>> while (!list_empty(done)) {
>>>> int cflags = 0;
>>>>
>>>> + if (READ_ONCE(req->result) == -EAGAIN) {
>>>> + req->iopoll_completed = 0;
>>>> + list_move_tail(&req->list, &again);
>>>> + continue;
>>>> + }
>>>> req = list_first_entry(done, struct io_kiocb, list);
>>>> list_del(&req->list);
>>>>
>>>
>>> You're using 'req' here before you initialize it...
>> Sorry, next time when I submit patches, I'll construct test cases which
>> will cover my codes changes.
>
> I'm surprised the compiler didn't complain, or that the regular testing
> didn't barf on it.
I'm also surprised, will try to find the reason.
And indeed the iopoll test case failed, but below command displayed nothing:
[lege@localhost test]$ sudo ./iopoll
Then I considered this test case pass wrongly.
dmesg show errors:
[ 127.806945] ==================================================================
[ 127.806983] BUG: KASAN: use-after-free in io_iopoll_complete+0xbb/0x980
[ 127.806989] Read of size 4 at addr ffff8886e3e98808 by task io_uring-sq/1643
[ 127.806999] CPU: 16 PID: 1643 Comm: io_uring-sq Not tainted 5.7.0+ #501
[ 127.807013] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014
[ 127.807021] Call Trace:
[ 127.807040] dump_stack+0x75/0xa0
[ 127.807047] ? io_iopoll_complete+0xbb/0x980
[ 127.807062] print_address_description.constprop.6+0x1a/0x220
[ 127.807086] ? _raw_write_lock_irqsave+0xd0/0xd0
[ 127.807092] ? io_free_req_many.part.79+0x208/0x2a0
[ 127.807107] ? __rcu_read_unlock+0x37/0x200
[ 127.807112] ? io_iopoll_complete+0xbb/0x980
[ 127.807117] ? io_iopoll_complete+0xbb/0x980
[ 127.807122] kasan_report.cold.9+0x1f/0x42
[ 127.807128] ? io_iopoll_complete+0xbb/0x980
[ 127.807133] io_iopoll_complete+0xbb/0x980
[ 127.807138] ? io_timeout_fn+0x140/0x140
[ 127.807150] ? __switch_to+0x2e9/0x5a0
[ 127.807157] io_iopoll_getevents+0x287/0x310
[ 127.807163] ? io_iopoll_complete+0x980/0x980
[ 127.807172] ? finish_wait+0xcb/0xf0
[ 127.807179] io_sq_thread+0x1c1/0x600
[ 127.807185] ? __ia32_sys_io_uring_enter+0x450/0x450
[ 127.807194] ? preempt_count_add+0x77/0xd0
[ 127.807200] ? _raw_spin_lock_irqsave+0x84/0xd0
[ 127.807206] ? _raw_write_lock_irqsave+0xd0/0xd0
[ 127.807210] ? finish_wait+0xf0/0xf0
[ 127.807215] ? preempt_count_sub+0x18/0xc0
[ 127.807224] ? __kthread_parkme+0xaf/0xd0
[ 127.807231] ? __ia32_sys_io_uring_enter+0x450/0x450
[ 127.807235] kthread+0x1e4/0x210
[ 127.807241] ? kthread_create_on_node+0xa0/0xa0
[ 127.807246] ret_from_fork+0x22/0x30
>
> Don't think you need a new test case for this, the iopoll test case
> should cover it, if you limit the queue depth on the device by
> setting /sys/block/<dev>/queue/nr_requests to 2 or something like
> that.
Thanks, I'll try later.
Regards,
Xiaoguang Wang
>
next prev parent reply other threads:[~2020-06-15 15:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 9:24 [PATCH 0/2] add proper memory barrier for IOPOLL mode Xiaoguang Wang
2020-06-15 9:24 ` [PATCH 1/2] io_uring: don't fail links for EAGAIN error in " Xiaoguang Wang
2020-06-15 9:24 ` [PATCH 2/2] io_uring: add memory barrier to synchronize io_kiocb's result and iopoll_completed Xiaoguang Wang
2020-06-15 14:36 ` Jens Axboe
2020-06-15 14:48 ` Xiaoguang Wang
2020-06-15 15:02 ` Jens Axboe
2020-06-15 15:09 ` Pavel Begunkov
2020-06-15 15:32 ` Xiaoguang Wang [this message]
2020-06-15 15:35 ` Jens Axboe
2020-06-15 16:51 ` Jens Axboe
2020-06-15 17:53 ` Xiaoguang Wang
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