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

[Jens Axboe <axboe@kernel.dk>]

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.

-- 
Jens Axboe