Re: [PATCH 5.8] io_uring: fix missing ->mm on exit

[Pavel Begunkov <asml.silence@gmail.com>]

On 24/08/2020 23:35, Pavel Begunkov wrote:
> do_exit() first drops current->mm and then runs task_work, from where
> io_sq_thread_acquire_mm() would try to set mm for a user dying process.

This is a backport of [1] + [2] for 5.8. Let's wait to see if
Roman Gershman can test it.

[1] 8eb06d7e8dd85 ("io_uring: fix missing ->mm on exit")
[2] cbcf72148da4a ("io_uring: return locked and pinned page accounting")


> 
> [  208.004249] WARNING: CPU: 2 PID: 1854 at
> 	kernel/kthread.c:1238 kthread_use_mm+0x244/0x270
> [  208.004287]  kthread_use_mm+0x244/0x270
> [  208.004288]  io_sq_thread_acquire_mm.part.0+0x54/0x80
> [  208.004290]  io_async_task_func+0x258/0x2ac
> [  208.004291]  task_work_run+0xc8/0x210
> [  208.004294]  do_exit+0x1b8/0x430
> [  208.004295]  do_group_exit+0x44/0xac
> [  208.004296]  get_signal+0x164/0x69c
> [  208.004298]  do_signal+0x94/0x1d0
> [  208.004299]  do_notify_resume+0x18c/0x340
> [  208.004300]  work_pending+0x8/0x3d4
> 
> Reported-by: Roman Gershman <>
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>  fs/io_uring.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 493e5047e67c..a8b3a608c553 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -4313,7 +4313,8 @@ static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,
>  				   struct io_kiocb *req)
>  {
>  	if (io_op_defs[req->opcode].needs_mm && !current->mm) {
> -		if (unlikely(!mmget_not_zero(ctx->sqo_mm)))
> +		if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) ||
> +			     !mmget_not_zero(ctx->sqo_mm)))
>  			return -EFAULT;
>  		kthread_use_mm(ctx->sqo_mm);
>  	}
> 

-- 
Pavel Begunkov