linux-kernel - Re: [PATCH] io_uring: handle signals before letting io-worker exit

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Message-ID: <3d1bd9e2-b711-0aac-628e-89b95ff8dbc3@kernel.dk>
Date:   Thu, 27 May 2021 07:46:44 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Olivier Langlois <olivier@...llion01.com>,
        Pavel Begunkov <asml.silence@...il.com>,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: handle signals before letting io-worker exit

On 5/26/21 12:21 PM, Olivier Langlois wrote:
> This is required for proper core dump generation.
> 
> Because signals are normally serviced before resuming userspace and an
> io_worker thread will never resume userspace, it needs to explicitly
> call the signal servicing functions.
> 
> Also, notice that it is possible to exit from the io_wqe_worker()
> function main loop while having a pending signal such as when
> the IO_WQ_BIT_EXIT bit is set.
> 
> It is crucial to service any pending signal before calling do_exit()
> Proper coredump generation is relying on PF_SIGNALED to be set.
> 
> More specifically, exit_mm() is using this flag to wait for the
> core dump completion before releasing its memory descriptor.
> 
> Signed-off-by: Olivier Langlois <olivier@...llion01.com>
> ---
>  fs/io-wq.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io-wq.c b/fs/io-wq.c
> index 5361a9b4b47b..b76c61e9aff2 100644
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -9,8 +9,6 @@
>  #include <linux/init.h>
>  #include <linux/errno.h>
>  #include <linux/sched/signal.h>
> -#include <linux/mm.h>
> -#include <linux/sched/mm.h>
>  #include <linux/percpu.h>
>  #include <linux/slab.h>
>  #include <linux/rculist_nulls.h>
> @@ -193,6 +191,26 @@ static void io_worker_exit(struct io_worker *worker)
>  
>  	kfree_rcu(worker, rcu);
>  	io_worker_ref_put(wqe->wq);
> +	/*
> +	 * Because signals are normally serviced before resuming userspace and an
> +	 * io_worker thread will never resume userspace, it needs to explicitly
> +	 * call the signal servicing functions.
> +	 *
> +	 * Also notice that it is possible to exit from the io_wqe_worker()
> +	 * function main loop while having a pending signal such as when
> +	 * the IO_WQ_BIT_EXIT bit is set.
> +	 *
> +	 * It is crucial to service any pending signal before calling do_exit()
> +	 * Proper coredump generation is relying on PF_SIGNALED to be set.
> +	 *
> +	 * More specifically, exit_mm() is using this flag to wait for the
> +	 * core dump completion before releasing its memory descriptor.
> +	 */
> +	if (signal_pending(current)) {
> +		struct ksignal ksig;
> +
> +		get_signal(&ksig);
> +	}
>  	do_exit(0);
>  }

Do we need the same thing in fs/io_uring.c:io_sq_thread()?

-- 
Jens Axboe