[PATCH 5.10 03/12] tick/nohz: unexport __init-annotated tick_nohz_full_setup()

[Greg Kroah-Hartman]

From: Masahiro Yamada <masahiroy@xxxxxxxxxx>

commit 2390095113e98fc52fffe35c5206d30d9efe3f78 upstream.

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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Backlund <tmb@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 kernel/time/tick-sched.c |    1 -
 1 file changed, 1 deletion(-)

--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -425,7 +425,6 @@ void __init tick_nohz_full_setup(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)
 {