• Peter Zijlstra's avatar
    sched/clock: Fix hotplug crash · acb04058
    Peter Zijlstra authored
    Mike reported that he could trigger the WARN_ON_ONCE() in
    set_sched_clock_stable() using hotplug.
    
    This exposed a fundamental problem with the interface, we should never
    mark the TSC stable if we ever find it to be unstable. Therefore
    set_sched_clock_stable() is a broken interface.
    
    The reason it existed is that not having it is a pain, it means all
    relevant architecture code needs to call clear_sched_clock_stable()
    where appropriate.
    
    Of the three architectures that select HAVE_UNSTABLE_SCHED_CLOCK ia64
    and parisc are trivial in that they never called
    set_sched_clock_stable(), so add an unconditional call to
    clear_sched_clock_stable() to them.
    
    For x86 the story is a lot more involved, and what this patch tries to
    do is ensure we preserve the status quo. So even is Cyrix or Transmeta
    have usable TSC they never called set_sched_clock_stable() so they now
    get an explicit mark unstable.
    Reported-by: default avatarMike Galbraith <efault@gmx.de>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Fixes: 9881b024 ("sched/clock: Delay switching sched_clock to stable")
    Link: http://lkml.kernel.org/r/20170119133633.GB6536@twins.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    acb04058
kvmclock.c 8.21 KB