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    SubjectRe: [PATCH] rcu: record kasan stack before enter local_irq_save()/restore() critical area
    On Sat, 25 Dec 2021 at 09:39, Zhang, Qiang1 <qiang1.zhang@intel.com> wrote:
    [...]
    > Hi Marco, Are the following modifications clear to you?

    I understood now that the contention you're talking about is from
    depot_lock, which wasn't clear before (I thought you intended to
    reduce contention by shortening some other critical section).

    > Subject: [PATCH] rcu: Reduce the consumption time of
    > local_irq_save()/restore() critical area

    Subject: rcu, kasan: Record work creation stack trace with interrupts enabled

    > In non-production KASAN kernel, a large number of call stacks are recorded,
    > it takes some time to acquire the global spinlock(depot_lock) inside
    > kasan_record_aux_stack_noalloc(), increased interrupts disable time,
    > kasan_record_aux_stack_noalloc() doesn't care if interrupts are enabled or
    > not when called, so move it outside the critical area.

    I think this might be clearer:

    "Recording the work creation stack trace for KASAN reports in
    call_rcu() is expensive, due to unwinding the stack, but also due to
    acquiring depot_lock inside stackdepot (which may be contended).
    Because calling kasan_record_aux_stack_noalloc() does not require
    interrupts to already be disabled, this may unnecessarily extend the
    time with interrupts disabled.

    Therefore, move calling kasan_record_aux_stack() before the section
    with interrupts disabled."

    > Signed-off-by: Zqiang <qiang1.zhang@intel.com>

    Acked-by: Marco Elver <elver@google.com>

    > ---
    > kernel/rcu/tree.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    > index 9b58bae0527a..36bd3f9e57b3 100644
    > --- a/kernel/rcu/tree.c
    > +++ b/kernel/rcu/tree.c
    > @@ -3068,8 +3068,8 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func)
    > }
    > head->func = func;
    > head->next = NULL;
    > - local_irq_save(flags);
    > kasan_record_aux_stack_noalloc(head);
    > + local_irq_save(flags);
    > rdp = this_cpu_ptr(&rcu_data);
    >
    > Thanks,
    > Zqiang

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