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

["christoph.plattner@gmx.at" <christoph.plattner@gmx.at>]

Hello Daniel,

I tested first the 6.18.17 kernel with my full patch, which was OK.
Then I re-started with a new kernel, added your patch and removed my 
"movel" from my patch, which I applied afterwards.
Kernel boots fine, shell running, even telnetd is running, all OK.

So, green light !

Thank you
Christoph


On 3/12/26 12:58, Daniel Palmer wrote:
> The logic for deciding what to do after a syscall should be checking
> if any of the lower word 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 just loads the whole
> of the flags, 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>
> ---
>
> I have had a variation of this patch for ages and haven't
> gotten around to sending it. Christoph e-mailed us (Greg, Sasha and me)
> to report this issue with a similar patch. Apparently this is an
> issue all the way back to 5.15.
>
> Christoph, can you check this works for you? I took this out of my
> personal branch and made sure it built but I have a bunch of other
> junk I need to actually boot it on the things I have.
>
>   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..cd193fd34c19 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 */
> +	movel	%a2@(TINFO_FLAGS),%d1	/* thread_info->flags */
>   	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
>