Re: [PATCH v2] m68k: Fix task info flags handling for 68000

[Greg Ungerer <gerg@linux-m68k.org>]

Hi Daniel,

On 4/4/26 12:31, Daniel Palmer wrote:
> The logic for deciding what to do after a syscall should be checking
> if any of the lower byte bits are set and then checking if the reschedule
> bit is set.
> 
> Currently we are loading the top word, checking if any bits are set
> (which never seems to be true) and thus jumping over loading the
> whole long and checking if the reschedule bit is set.
> 
> We get the thread info in two places so split that logic out in
> a macro and then fix the code so that it loads the byte of the flags
> we need to check, checks if anything is set and then checks if
> the reschedule bit in particular is set.
> 
> Reported-by: Christoph Plattner <christoph.plattner@gmx.at>
> Signed-off-by: Daniel Palmer <daniel@0x0f.com>
> ---
> v2: Only load the lower byte of the flags as that's all we need.
>      This change was suggested by Greg and I tested it still works.

Thanks for taking care of this.
I have pushed into the m68knommu git tree for-next branch.

Regards
Greg



>   arch/m68k/68000/entry.S | 21 +++++++++++++--------
>   1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/m68k/68000/entry.S b/arch/m68k/68000/entry.S
> index 72e95663b62f..c257cc415c47 100644
> --- a/arch/m68k/68000/entry.S
> +++ b/arch/m68k/68000/entry.S
> @@ -18,6 +18,13 @@
>   
>   .text
>   
> +/* get thread_info pointer into a2 */
> + .macro getthreadinfo
> +	movel	%sp,%d1
> +	andl	#-THREAD_SIZE,%d1
> +	movel	%d1,%a2
> + .endm
> +
>   .globl system_call
>   .globl resume
>   .globl ret_from_exception
> @@ -70,9 +77,8 @@ ENTRY(system_call)
>   
>   	movel	%sp@(PT_OFF_ORIG_D0),%d0
>   
> -	movel	%sp,%d1			/* get thread_info pointer */
> -	andl	#-THREAD_SIZE,%d1
> -	movel	%d1,%a2
> +	/* Doing a trace ? */
> +	getthreadinfo
>   	btst	#(TIF_SYSCALL_TRACE%8),%a2@(TINFO_FLAGS+(31-TIF_SYSCALL_TRACE)/8)
>   	jne	do_trace
>   	cmpl	#NR_syscalls,%d0
> @@ -96,16 +102,15 @@ Luser_return:
>   	/* heavy interrupt load*/
>   	andw	#ALLOWINT,%sr
>   
> -	movel	%sp,%d1			/* get thread_info pointer */
> -	andl	#-THREAD_SIZE,%d1
> -	movel	%d1,%a2
> +	getthreadinfo
>   1:
> -	move	%a2@(TINFO_FLAGS),%d1	/* thread_info->flags */
> +	/* check if any of the flags are set */
> +	moveb	%a2@(TINFO_FLAGS + 3),%d1	/* thread_info->flags (low 8 bits) */
>   	jne	Lwork_to_do
>   	RESTORE_ALL
>   
>   Lwork_to_do:
> -	movel	%a2@(TINFO_FLAGS),%d1	/* thread_info->flags */
> +	/* check if reschedule needs to be called */
>   	btst	#TIF_NEED_RESCHED,%d1
>   	jne	reschedule
>