tick/nohz: unexport __init-annotated tick_nohz_full_setup()
authorMasahiro Yamada <masahiroy@kernel.org>
Mon, 27 Jun 2022 03:22:09 +0000 (12:22 +0900)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sat, 2 Jul 2022 14:41:12 +0000 (16:41 +0200)
commitf4a80ec8c51d68be4b7a7830c510f75080c5e417
tree7dc5882e4847a911f9192158e7c6e2829505371c
parent37238449af786e1be06f193ab54a60a39a776826
tick/nohz: unexport __init-annotated tick_nohz_full_setup()

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@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Backlund <tmb@tmb.nu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/time/tick-sched.c