Re: [PATCH] io_uring: use cond_resched() in io_ring_ctx_wait_and_kill()

[Jens Axboe <axboe@kernel.dk>]

On 4/30/20 6:52 PM, Xiaoguang Wang wrote:
> While working on to make io_uring sqpoll mode support syscalls that need
> struct files_struct, I got cpu soft lockup in io_ring_ctx_wait_and_kill(),
>     while (ctx->sqo_thread && !wq_has_sleeper(&ctx->sqo_wait))
>         cpu_relax();
> above loop never has an chance to exit, it's because preempt isn't enabled
> in the kernel, and the context calling io_ring_ctx_wait_and_kill() and
> io_sq_thread() run in the same cpu, if io_sq_thread calls a cond_resched()
> yield cpu and another context enters above loop, then io_sq_thread() will
> always in runqueue and never exit.
> 
> Use cond_resched() can fix this issue.

Thanks, this looks good, I believe it should also fix the syzbot reported
issue so I added the tag for that.

-- 
Jens Axboe