linux-kernel - Re: [PATCH AUTOSEL 5.11 42/44] signal: don't allow sending any signals to PF_IO

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Date:   Thu, 25 Mar 2021 12:32:43 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH AUTOSEL 5.11 42/44] signal: don't allow sending any
 signals to PF_IO_WORKER threads

Am 25.03.21 um 12:24 schrieb Sasha Levin:
> From: Jens Axboe <axboe@...nel.dk>
> 
> [ Upstream commit 5be28c8f85ce99ed2d329d2ad8bdd18ea19473a5 ]
> 
> They don't take signals individually, and even if they share signals with
> the parent task, don't allow them to be delivered through the worker
> thread. Linux does allow this kind of behavior for regular threads, but
> it's really a compatability thing that we need not care about for the IO
> threads.
> 
> Reported-by: Stefan Metzmacher <metze@...ba.org>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  kernel/signal.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/signal.c b/kernel/signal.c
> index 5ad8566534e7..55526b941011 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -833,6 +833,9 @@ static int check_kill_permission(int sig, struct kernel_siginfo *info,
>  
>  	if (!valid_signal(sig))
>  		return -EINVAL;
> +	/* PF_IO_WORKER threads don't take any signals */
> +	if (t->flags & PF_IO_WORKER)
> +		return -ESRCH;

Why is that proposed for 5.11 and 5.10 now?

Are the create_io_thread() patches already backported?

I think we should hold on with the backports until
everything is stable in v5.12 final.

I'm still about to test on top of v5.12-rc4
and have a pending mail why I think this particular change is
wrong even in 5.12.

Jens, did you send these to stable?

metze