linux-kernel - Re: [PATCH] MIPS: mm: abort uaccess retries upon fatal signal

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Message-ID: <20210122104948.GB8146@alpha.franken.de>
Date:   Fri, 22 Jan 2021 11:49:48 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] MIPS: mm: abort uaccess retries upon fatal signal

On Thu, Jan 21, 2021 at 05:04:16PM +0100, Thomas Bogendoerfer wrote:
> When there's a fatal signal pending, MIPS's do_page_fault()
> implementation returns. The intent is that we'll return to the
> faulting userspace instruction, delivering the signal on the way.
> 
> However, if we take a fatal signal during fixing up a uaccess, this
> results in a return to the faulting kernel instruction, which will be
> instantly retried, resulting in the same fault being taken forever. As
> the task never reaches userspace, the signal is not delivered, and the
> task is left unkillable. While the task is stuck in this state, it can
> inhibit the forward progress of the system.
> 
> To avoid this, we must ensure that when a fatal signal is pending, we
> apply any necessary fixup for a faulting kernel instruction. Thus we
> will return to an error path, and it is up to that code to make forward
> progress towards delivering the fatal signal.
> 
> [ Description taken from commit 746a272e4414 ("ARM: 8692/1: mm: abort
>    uaccess retries upon fatal signal") ]
> 
> Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> ---
>  arch/mips/mm/fault.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

applied to mips-next.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]