linux-kernel - Re: [PATCH] kmemleak: fix check for softirq context

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Message-ID: <20190518094719.gyvhbdrwmcv4diax@mbp>
Date:   Sat, 18 May 2019 10:47:20 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...il.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kmemleak: fix check for softirq context

On Sat, May 18, 2019 at 09:10:59AM +0200, Dmitry Vyukov wrote:
> On Fri, May 17, 2019 at 11:37 PM Andrew Morton
> <akpm@...ux-foundation.org> wrote:
> > On Fri, 17 May 2019 19:15:07 +0200 Dmitry Vyukov <dvyukov@...il.com> wrote:
> >
> > > From: Dmitry Vyukov <dvyukov@...gle.com>
> > >
> > > in_softirq() is a wrong predicate to check if we are in a softirq context.
> > > It also returns true if we have BH disabled, so objects are falsely
> > > stamped with "softirq" comm. The correct predicate is in_serving_softirq().
> > >
> > > ...
> > >
> > > --- a/mm/kmemleak.c
> > > +++ b/mm/kmemleak.c
> > > @@ -588,7 +588,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
> > >       if (in_irq()) {
> > >               object->pid = 0;
> > >               strncpy(object->comm, "hardirq", sizeof(object->comm));
> > > -     } else if (in_softirq()) {
> > > +     } else if (in_serving_softirq()) {
> > >               object->pid = 0;
> > >               strncpy(object->comm, "softirq", sizeof(object->comm));
> > >       } else {
> >
> > What are the user-visible runtime effects of this change?
> 
> If user does cat from /sys/kernel/debug/kmemleak previously they would
> see this, which is clearly wrong, this is system call context (see the
> comm):

Indeed, with your patch you get the correct output.

Acked-by: Catalin Marinas <catalin.marinas@....com>

Thanks.

-- 
Catalin