RE: [PATCH] test/defer: fix deadlock when io_uring_submit fail

[lizetao <lizetao1@huawei.com>]

Hi,

> -----Original Message-----
> From: Jens Axboe <axboe@kernel.dk>
> Sent: Thursday, January 16, 2025 10:51 PM
> To: lizetao <lizetao1@huawei.com>; Pavel Begunkov <asml.silence@gmail.com>
> Cc: io-uring@vger.kernel.org
> Subject: Re: [PATCH] test/defer: fix deadlock when io_uring_submit fail
> 
> On 1/15/25 6:10 AM, lizetao wrote:
> > While performing fault injection testing, a bug report was triggered:
> >
> >   FAULT_INJECTION: forcing a failure.
> >   name fail_usercopy, interval 1, probability 0, space 0, times 0
> >   CPU: 12 UID: 0 PID: 18795 Comm: defer.t Tainted: G           O
> 6.13.0-rc6-gf2a0a37b174b #17
> >   Tainted: [O]=OOT_MODULE
> >   Hardware name: linux,dummy-virt (DT)
> >   Call trace:
> >    show_stack+0x20/0x38 (C)
> >    dump_stack_lvl+0x78/0x90
> >    dump_stack+0x1c/0x28
> >    should_fail_ex+0x544/0x648
> >    should_fail+0x14/0x20
> >    should_fail_usercopy+0x1c/0x28
> >    get_timespec64+0x7c/0x258
> >    __io_timeout_prep+0x31c/0x798
> >    io_link_timeout_prep+0x1c/0x30
> >    io_submit_sqes+0x59c/0x1d50
> >    __arm64_sys_io_uring_enter+0x8dc/0xfa0
> >    invoke_syscall+0x74/0x270
> >    el0_svc_common.constprop.0+0xb4/0x240
> >    do_el0_svc+0x48/0x68
> >    el0_svc+0x38/0x78
> >    el0t_64_sync_handler+0xc8/0xd0
> >    el0t_64_sync+0x198/0x1a0
> >
> > The deadlock stack is as follows:
> >
> >   io_cqring_wait+0xa64/0x1060
> >   __arm64_sys_io_uring_enter+0x46c/0xfa0
> >   invoke_syscall+0x74/0x270
> >   el0_svc_common.constprop.0+0xb4/0x240
> >   do_el0_svc+0x48/0x68
> >   el0_svc+0x38/0x78
> >   el0t_64_sync_handler+0xc8/0xd0
> >   el0t_64_sync+0x198/0x1a0
> >
> > This is because after the submission fails, the defer.t testcase is still waiting to
> submit the failed request, resulting in an eventual deadlock.
> > Solve the problem by telling wait_cqes the number of requests to wait for.
> 
> I suspect this would be fixed by setting IORING_SETUP_SUBMIT_ALL for ring init,
> something probably all/most tests should set.


I tested it and found that IORING_SETUP_SUBMIT_ALL can indeed solve this problem. 
Should I just modify this problem or add IORING_SETUP_SUBMIT_ALL to the general path to
solve most possible problems?
> 
> --
> Jens Axboe

---
Li Zetao