Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 19 Sep 2017 14:57:22 +0200 | Subject | Re: [PATCH 3/3] kcov: remove useless barrier()s |
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On Tue, Sep 19, 2017 at 2:46 PM, Andrey Ryabinin <aryabinin@virtuozzo.com> wrote: > As comment says barriers needed for preempt_schedule_irq() case > where in_interrupt() returns false. But we don't use in_interrupt() > since b274c0bb394c ("kcov: properly check if we are in an interrupt"). > > Now we use in_task() which handles preempt_schedule_irq() case properly, > thus no barrier required.
Are you sure in_task() handles preempt_schedule_irq() correctly? They seem to differ only by SOFTIRQ_MASK vs SOFTIRQ_OFFSET, and that only differs in local_bh_disable sections. But preempt_schedule_irq() does not seem to have anything to do softirq/local_bh_disable. It's called from real interrupts, right? So I would expect that in_task() returns true in preempt_schedule_irq().
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> > --- > kernel/kcov.c | 10 ---------- > 1 file changed, 10 deletions(-) > > diff --git a/kernel/kcov.c b/kernel/kcov.c > index 14cc8c1a7cad..b7fbcbef88c1 100644 > --- a/kernel/kcov.c > +++ b/kernel/kcov.c > @@ -71,14 +71,6 @@ void notrace __sanitizer_cov_trace_pc(void) > > ip -= kaslr_offset(); > > - /* > - * There is some code that runs in interrupts but for which > - * in_interrupt() returns false (e.g. preempt_schedule_irq()). > - * READ_ONCE()/barrier() effectively provides load-acquire wrt > - * interrupts, there are paired barrier()/WRITE_ONCE() in > - * kcov_ioctl_locked(). > - */ > - barrier(); > area = t->kcov_area; > /* The first word is number of subsequent PCs. */ > pos = READ_ONCE(area[0]) + 1; > @@ -228,8 +220,6 @@ static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd, > /* Cache in task struct for performance. */ > t->kcov_size = kcov->size; > t->kcov_area = kcov->area; > - /* See comment in __sanitizer_cov_trace_pc(). */ > - barrier(); > WRITE_ONCE(t->kcov_mode, kcov->mode); > t->kcov = kcov; > kcov->t = t; > -- > 2.13.5 >
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