tick/nohz: unexport __init-annotated tick_nohz_full_setup()

23900951 · Masahiro Yamada <[email protected]> · 2022-06-27 12:22:09 +09:00

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 <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Tested-by: Paul E. McKenney <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 2390095113e98fc52fffe35c5206d30d9efe3f78
Parents: 03c765b0

Changes

1 files changed · +0 −1

File	Status	Add	Del	Content
kernel/time/tick-sched.c	modified	+0	−1	View file

kernel/time/tick-sched.c

View file

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 58a11f8..3004958 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)
 {