* [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup()
@ 2022-06-27 3:22 Masahiro Yamada
2022-06-27 3:37 ` Paul E. McKenney
2022-06-27 17:44 ` Linus Torvalds
0 siblings, 2 replies; 3+ messages in thread
From: Masahiro Yamada @ 2022-06-27 3:22 UTC (permalink / raw)
To: Frederic Weisbecker, Thomas Gleixner, Ingo Molnar, linux-kernel,
Paul E . McKenney
Cc: Linus Torvalds, Masahiro Yamada
EXPORT_SYMBOL and __init is a bad combination because the .init.text
section is freed up after the initialization. Hence, modules cannot
use symbols annotated __init. The access to a freed symbol may end up
with kernel panic.
modpost used to detect it, but it had been broken for a decade.
Commit 28438794aba4 ("modpost: fix section mismatch check for exported
init/exit sections") fixed it so modpost started to warn it again, then
this showed up:
MODPOST vmlinux.symvers
WARNING: modpost: vmlinux.o(___ksymtab_gpl+tick_nohz_full_setup+0x0): Section mismatch in reference from the variable __ksymtab_tick_nohz_full_setup to the function .init.text:tick_nohz_full_setup()
The symbol tick_nohz_full_setup is exported and annotated __init
Fix this by removing the __init annotation of tick_nohz_full_setup or drop the export.
Drop the export because tick_nohz_full_setup() is only called from the
built-in code in kernel/sched/isolation.c.
Fixes: ae9e557b5be2 ("time: Export tick start/stop functions for rcutorture")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---
kernel/time/tick-sched.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 58a11f859ac7..30049580cd62 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -526,7 +526,6 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask)
cpumask_copy(tick_nohz_full_mask, cpumask);
tick_nohz_full_running = true;
}
-EXPORT_SYMBOL_GPL(tick_nohz_full_setup);
static int tick_nohz_cpu_down(unsigned int cpu)
{
--
2.32.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup()
2022-06-27 3:22 [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup() Masahiro Yamada
@ 2022-06-27 3:37 ` Paul E. McKenney
2022-06-27 17:44 ` Linus Torvalds
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2022-06-27 3:37 UTC (permalink / raw)
To: Masahiro Yamada
Cc: Frederic Weisbecker, Thomas Gleixner, Ingo Molnar, linux-kernel,
Linus Torvalds
On Mon, Jun 27, 2022 at 12:22:09PM +0900, Masahiro Yamada wrote:
> EXPORT_SYMBOL and __init is a bad combination because the .init.text
> section is freed up after the initialization. Hence, modules cannot
> use symbols annotated __init. The access to a freed symbol may end up
> with kernel panic.
>
> modpost used to detect it, but it had been broken for a decade.
>
> Commit 28438794aba4 ("modpost: fix section mismatch check for exported
> init/exit sections") fixed it so modpost started to warn it again, then
> this showed up:
>
> MODPOST vmlinux.symvers
> WARNING: modpost: vmlinux.o(___ksymtab_gpl+tick_nohz_full_setup+0x0): Section mismatch in reference from the variable __ksymtab_tick_nohz_full_setup to the function .init.text:tick_nohz_full_setup()
> The symbol tick_nohz_full_setup is exported and annotated __init
> Fix this by removing the __init annotation of tick_nohz_full_setup or drop the export.
>
> Drop the export because tick_nohz_full_setup() is only called from the
> built-in code in kernel/sched/isolation.c.
>
> Fixes: ae9e557b5be2 ("time: Export tick start/stop functions for rcutorture")
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
I went through my email and notes, and cannot find whatever it was that
possessed me to add tick_nohz_full_setup() to ae9e557b5be2. The other
two symbols have clear motivations. Apologies for the noise!!!
Thanx, Paul
> ---
>
> kernel/time/tick-sched.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 58a11f859ac7..30049580cd62 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -526,7 +526,6 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask)
> cpumask_copy(tick_nohz_full_mask, cpumask);
> tick_nohz_full_running = true;
> }
> -EXPORT_SYMBOL_GPL(tick_nohz_full_setup);
>
> static int tick_nohz_cpu_down(unsigned int cpu)
> {
> --
> 2.32.0
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup()
2022-06-27 3:22 [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup() Masahiro Yamada
2022-06-27 3:37 ` Paul E. McKenney
@ 2022-06-27 17:44 ` Linus Torvalds
1 sibling, 0 replies; 3+ messages in thread
From: Linus Torvalds @ 2022-06-27 17:44 UTC (permalink / raw)
To: Masahiro Yamada
Cc: Frederic Weisbecker, Thomas Gleixner, Ingo Molnar,
Linux Kernel Mailing List, Paul E . McKenney
On Sun, Jun 26, 2022 at 8:22 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> Drop the export because tick_nohz_full_setup() is only called from the
> built-in code in kernel/sched/isolation.c.
Thanks, applied.
Linus
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-06-27 17:44 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-06-27 3:22 [PATCH] tick/nohz: unexport __init-annotated tick_nohz_full_setup() Masahiro Yamada
2022-06-27 3:37 ` Paul E. McKenney
2022-06-27 17:44 ` Linus Torvalds
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.