Messages in this thread | | | From | Marco Elver <> | Date | Sat, 25 Dec 2021 10:36:03 +0100 | Subject | Re: [PATCH] rcu: record kasan stack before enter local_irq_save()/restore() critical area |
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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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