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    Subject[PATCH 5.10 03/12] tick/nohz: unexport __init-annotated tick_nohz_full_setup()
    Date
    From: Masahiro Yamada <masahiroy@kernel.org>

    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 | 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)
    {

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