Re: [PATCH 1/1] ppc64: fix missing to check all bits of _TIF_USER_WORK_MASK in preempt

["tiejun.chen" <tiejun.chen@windriver.com>]

Tiejun Chen wrote:
> In entry_64.S version of ret_from_except_lite, you'll notice that
> in the !preempt case, after we've checked MSR_PR we test for any
> TIF flag in _TIF_USER_WORK_MASK to decide whether to go to do_work
> or not. However, in the preempt case, we do a convoluted trick to
> test SIGPENDING only if PR was set and always test NEED_RESCHED ...
> but we forget to test any other bit of _TIF_USER_WORK_MASK !!! So
> that means that with preempt, we completely fail to test for things
> like single step, syscall tracing, etc...
> 
> This should be fixed as the following path:
> 
>  - Test PR. If set, go to test_work_user, else continue.
> 
>  - In test_work_user, always test for _TIF_USER_WORK_MASK to decide to
> go to do_work, maybe call it do_user_work
> 
>  - In test_work_kernel, test for _TIF_KERNEL_WORK_MASK which is set to
> our new flag along with NEED_RESCHED if preempt is enabled and branch to
> do_kernel_work.

Ben,

Any comment for this?

Tiejun

> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Tiejun Chen <tiejun.chen@windriver.com>
> ---
>  arch/powerpc/kernel/entry_64.S |   33 +++++++++++++++------------------
>  1 files changed, 15 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index d834425..9e70b9a 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -571,27 +571,26 @@ _GLOBAL(ret_from_except_lite)
>  	mtmsrd	r9,1		/* Update machine state */
>  #endif /* CONFIG_PPC_BOOK3E */
>  
> -#ifdef CONFIG_PREEMPT
> -	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> -	li	r0,_TIF_NEED_RESCHED	/* bits to check */
> -	ld	r3,_MSR(r1)
> -	ld	r4,TI_FLAGS(r9)
> -	/* Move MSR_PR bit in r3 to _TIF_SIGPENDING position in r0 */
> -	rlwimi	r0,r3,32+TIF_SIGPENDING-MSR_PR_LG,_TIF_SIGPENDING
> -	and.	r0,r4,r0	/* check NEED_RESCHED and maybe SIGPENDING */
> -	bne	do_work
> -
> -#else /* !CONFIG_PREEMPT */
>  	ld	r3,_MSR(r1)	/* Returning to user mode? */
>  	andi.	r3,r3,MSR_PR
> -	beq	restore		/* if not, just restore regs and return */
> +	bne	test_work_user
>  
> +	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
> +	li	r0,_TIF_USER_WORK_MASK
> +#ifdef CONFIG_PREEMPT
> +	ori	r0,r0,_TIF_NEED_RESCHED
> +#endif
> +	ld	r4,TI_FLAGS(r9)
> +	and.	r0,r4,r0	/* check NEED_RESCHED and maybe _TIF_USER_WORK_MASK */
> +	bne	do_kernel_work
> +	b	restore		/* if so, just restore regs and return */
> +
> +test_work_user:
>  	/* Check current_thread_info()->flags */
>  	clrrdi	r9,r1,THREAD_SHIFT
>  	ld	r4,TI_FLAGS(r9)
>  	andi.	r0,r4,_TIF_USER_WORK_MASK
> -	bne	do_work
> -#endif
> +	bne	do_user_work
>  
>  restore:
>  BEGIN_FW_FTR_SECTION
> @@ -693,10 +692,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>  	b	.ret_from_except_lite		/* loop back and handle more */
>  #endif
>  
> -do_work:
> +do_kernel_work:
>  #ifdef CONFIG_PREEMPT
> -	andi.	r0,r3,MSR_PR	/* Returning to user mode? */
> -	bne	user_work
>  	/* Check that preempt_count() == 0 and interrupts are enabled */
>  	lwz	r8,TI_PREEMPT(r9)
>  	cmpwi	cr1,r8,0
> @@ -738,9 +735,9 @@ do_work:
>  	bne	1b
>  	b	restore
>  
> -user_work:
>  #endif /* CONFIG_PREEMPT */
>  
> +do_user_work:
>  	/* Enable interrupts */
>  #ifdef CONFIG_PPC_BOOK3E
>  	wrteei	1