Subject: Re: linux-next: build failure after merge of the tip tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 31 Oct 2025 12:18:12 +1100

Hi all,

On Fri, 31 Oct 2025 12:02:43 +1100 Stephen Rothwell <[email-masked]> wrote:
>
> After merging the tip tree, today's linux-next build (arm64 defconfig)
> failed like this:
> 
> arch/arm64/kernel/entry-common.c: In function 'arm64_exit_to_user_mode':
> arch/arm64/kernel/entry-common.c:103:9: error: implicit declaration of function 'exit_to_user_mode_prepare'; did you mean 'arch_exit_to_user_mode_prepare'? [-Wimplicit-function-declaration]
>   103 |         exit_to_user_mode_prepare(regs);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~
>       |         arch_exit_to_user_mode_prepare
> In file included from arch/arm64/include/asm/current.h:5,
>                  from include/linux/sched.h:12,
>                  from include/linux/context_tracking.h:5,
>                  from include/linux/irq-entry-common.h:5,
>                  from kernel/entry/common.c:3:
> kernel/entry/common.c: In function 'exit_to_user_mode_loop':
> kernel/entry/common.c:77:29: error: implicit declaration of function 'rseq_exit_to_user_mode_restart'; did you mean 'arch_exit_to_user_mode_prepare'? [-Wimplicit-function-declaration]
>    77 |                 if (likely(!rseq_exit_to_user_mode_restart(regs, ti_work)))
>       |                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> include/linux/compiler.h:76:45: note: in definition of macro 'likely'
>    76 | # define likely(x)      __builtin_expect(!!(x), 1)
>       |                                             ^
> 
> Caused by commit
> 
>   d58930640310 ("entry: Split up exit_to_user_mode_prepare()")
> 
> and maybe following ones.
> 
> I have reverted these commits for today:
> 
>   69c8e3d16105 ("rseq: Switch to TIF_RSEQ if supported")
>   1b3dd1c538a8 ("rseq: Split up rseq_exit_to_user_mode()")
>   d58930640310 ("entry: Split up exit_to_user_mode_prepare()")

I also had to revert

  84eeeb002035 ("rseq: Switch to fast path processing on exit to user")

-- 
Cheers,
Stephen Rothwell