linux-kernel - Re: [PATCH 1/3] CRISv32: don't attempt syscall restart on irq exit

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Date:	Mon, 9 Feb 2015 10:49:54 +0100
From:	Jesper Nilsson <jesper.nilsson@...s.com>
To:	Rabin Vincent <rabin@....in>
Cc:	jespern@...s.com, linux-cris-kernel@...s.com,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] CRISv32: don't attempt syscall restart on irq exit

On Sun, Feb 08, 2015 at 09:45:02PM +0100, Rabin Vincent wrote:
> r9 is used to determine whether syscall restarting must be performed or
> not.  Unfortunately, r9 is never set to zero in the non-syscall path,
> and r9 is on top of that a callee-saved register which can be set to
> non-zero by the C functions that are called during IRQ handling.
> 
> This means that if r10 (used for the syscall return value) is one of the
> -ERESTART* values when a hardware interrupt occurs which leads to a
> signal being delivered to the process, the kernel will "restart" a
> syscall which never occurred.  This will lead to the PC being moved back
> by 2 on return to user space.
> 
> Fix the problem by setting r9 to zero in the interrupt path.
> 
> Test case (should loop forever but ends up executing the break 8 trap
> instruction):
> 
>   #include <signal.h>
>   #include <stdlib.h>
>   #include <sys/time.h>
> 
>   void f(int n)
>   {
>   	register int r9 asm ("r9") = 1;
>   	register int r10 asm ("r10") = n;
> 
>           __asm__ __volatile__(
>   		"ba	1f	\n"
>   		"nop		\n"
>   		"break	8	\n"
>   		"1: ba	.	\n"
>   		"nop		\n"
>   		:
>   		: "r" (r9), "r" (r10)
>   		: "memory");
>   }
> 
>   void handler1(int sig) { }
> 
>   int main(int argc, char *argv[])
>   {
>           struct itimerval t1 = { .it_value = {1} };
> 
>           signal(SIGALRM, handler1);
>           setitimer(ITIMER_REAL, &t1, NULL);
> 
>           f(-513); /* -ERESTARTNOINTR */
> 
>           return 0;
>   }
> 
> Signed-off-by: Rabin Vincent <rabin@....in>

Nice, added in the CRIS tree for 3.20.

/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- jesper.nilsson@...s.com
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