[PATCH] arm: cacheflush: get rid of restarting block

[Chanho Min]

> -----Original Message-----
> From: Vladimir Murzin [mailto:vladimir.murzin at arm.com]
> Sent: Wednesday, November 26, 2014 12:19 AM
> To: linux-arm-kernel at lists.infradead.org; linux at arm.linux.org.uk
> Cc: chanho.min at lge.com; will.deacon at arm.com; stable at vger.kernel.org
> Subject: [PATCH] arm: cacheflush: get rid of restarting block
> 
> We cannot restart cacheflush safely if a process provides user-defined
> signal handler and signal is pending. In this case -EINTR is returned
> and it is expected that process re-invokes syscall. However, there are
> a few problems with that:
>  * looks like nobody bothers checking return value from cacheflush
>  * but if it did, we don't provide the restart address for that, so the
>    process has to use the same range again
>  * ...and again, what might lead to looping forever
> 
> So, remove cacheflush restarting code and terminate cache flushing
> as early as fatal signal is pending.
> 
> Cc: stable at vger.kernel.org # 3.12+
> Reported-by: Chanho Min <chanho.min at lge.com>
> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
> Acked-by: Will Deacon <will.deacon at arm.com>
> ---
> Hi,
> 
> There is my proposal for the problem reported in [1]. Since that
> thread has not been progressing much, I'm addressing the problem in
> separate patch.
> 
> Comments?
Thanks, We hope this to be applied.

> 
> [1] https://lkml.org/lkml/2014/11/13/29
> 
>  arch/arm/include/asm/thread_info.h |   11 -----------
>  arch/arm/kernel/traps.c            |   31 ++-----------------------------
>  2 files changed, 2 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
> index fc44d37..ce73ab6 100644
> --- a/arch/arm/include/asm/thread_info.h
> +++ b/arch/arm/include/asm/thread_info.h
> @@ -44,16 +44,6 @@ struct cpu_context_save {
>  	__u32	extra[2];		/* Xscale 'acc' register, etc */
>  };
> 
> -struct arm_restart_block {
> -	union {
> -		/* For user cache flushing */
> -		struct {
> -			unsigned long start;
> -			unsigned long end;
> -		} cache;
> -	};
> -};
> -
>  /*
>   * low level task data that entry.S needs immediate access to.
>   * __switch_to() assumes cpu_context follows immediately after cpu_domain.
> @@ -79,7 +69,6 @@ struct thread_info {
>  	unsigned long		thumbee_state;	/* ThumbEE Handler Base register */
>  #endif
>  	struct restart_block	restart_block;
> -	struct arm_restart_block	arm_restart_block;
>  };
> 
>  #define INIT_THREAD_INFO(tsk)						\
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 0c8b108..8dd03ee 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -533,8 +533,6 @@ static int bad_syscall(int n, struct pt_regs *regs)
>  	return regs->ARM_r0;
>  }
> 
> -static long do_cache_op_restart(struct restart_block *);
> -
>  static inline int
>  __do_cache_op(unsigned long start, unsigned long end)
>  {
> @@ -543,24 +541,8 @@ __do_cache_op(unsigned long start, unsigned long end)
>  	do {
>  		unsigned long chunk = min(PAGE_SIZE, end - start);
> 
> -		if (signal_pending(current)) {
> -			struct thread_info *ti = current_thread_info();
> -
> -			ti->restart_block = (struct restart_block) {
> -				.fn	= do_cache_op_restart,
> -			};
> -
> -			ti->arm_restart_block = (struct arm_restart_block) {
> -				{
> -					.cache = {
> -						.start	= start,
> -						.end	= end,
> -					},
> -				},
> -			};
> -
> -			return -ERESTART_RESTARTBLOCK;
> -		}
> +		if (fatal_signal_pending(current))
> +			return 0;
> 
>  		ret = flush_cache_user_range(start, start + chunk);
>  		if (ret)
> @@ -573,15 +555,6 @@ __do_cache_op(unsigned long start, unsigned long end)
>  	return 0;
>  }
> 
> -static long do_cache_op_restart(struct restart_block *unused)
> -{
> -	struct arm_restart_block *restart_block;
> -
> -	restart_block = &current_thread_info()->arm_restart_block;
> -	return __do_cache_op(restart_block->cache.start,
> -			     restart_block->cache.end);
> -}
> -
>  static inline int
>  do_cache_op(unsigned long start, unsigned long end, int flags)
>  {
> --
> 1.7.9.5
Chanho