From: Tri Vo <trong@android.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Hridya Valsaraju <hridya@google.com>,
Sandeep Patil <sspatil@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
"Cc: Android Kernel" <kernel-team@android.com>
Subject: Re: [PATCH] PM / wakeup: show wakeup sources stats in sysfs
Date: Wed, 26 Jun 2019 15:26:38 -0700 [thread overview]
Message-ID: <CANA+-vDOBrgUB5s2Y3stw4NhwMopwdVZq_WcgBSwNrWpNV=T9g@mail.gmail.com> (raw)
In-Reply-To: <20190626014633.GA22610@kroah.com>
On Tue, Jun 25, 2019 at 6:48 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Tue, Jun 25, 2019 at 06:33:08PM -0700, Tri Vo wrote:
> > On Tue, Jun 25, 2019 at 6:12 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > > +static ssize_t wakeup_source_count_show(struct wakeup_source *ws,
> > > > + struct wakeup_source_attribute *attr,
> > > > + char *buf)
> > > > +{
> > > > + unsigned long flags;
> > > > + unsigned long var;
> > > > +
> > > > + spin_lock_irqsave(&ws->lock, flags);
> > > > + if (strcmp(attr->attr.name, "active_count") == 0)
> > > > + var = ws->active_count;
> > > > + else if (strcmp(attr->attr.name, "event_count") == 0)
> > > > + var = ws->event_count;
> > > > + else if (strcmp(attr->attr.name, "wakeup_count") == 0)
> > > > + var = ws->wakeup_count;
> > > > + else
> > > > + var = ws->expire_count;
> > > > + spin_unlock_irqrestore(&ws->lock, flags);
> > > > +
> > > > + return sprintf(buf, "%lu\n", var);
> > > > +}
> > >
> > > Why is this lock always needed to be grabbed? You are just reading a
> > > value, who cares if it changes inbetween reading it and returning the
> > > buffer string as it can change at that point in time anyway?
> >
> > Right, we don't care if the value changes in between us reading and
> > printing it. However, IIUC not grabbing this lock results in a data
> > race, which is undefined behavior.
>
> A data race where? Writing to the value? How can that happen? All you
> are doing is incrementing this variable elsewhere, what is the worst
> that can happen?
Ok, I'll remove the locks.
next prev parent reply other threads:[~2019-06-26 22:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 0:54 [PATCH] PM / wakeup: show wakeup sources stats in sysfs Tri Vo
2019-06-26 0:59 ` Tri Vo
2019-06-26 1:12 ` Greg KH
2019-06-26 1:33 ` Tri Vo
2019-06-26 1:46 ` Greg KH
2019-06-26 22:26 ` Tri Vo [this message]
2019-06-26 22:48 ` Tri Vo
2019-06-27 0:04 ` Greg KH
2019-06-27 22:53 ` [PATCH v2] " Tri Vo
2019-06-28 15:10 ` Greg KH
2019-07-04 10:31 ` Rafael J. Wysocki
2019-07-08 3:33 ` Tri Vo
2019-07-15 20:11 ` [PATCH v3] " Tri Vo
2019-07-15 20:36 ` Greg KH
2019-07-15 21:43 ` [PATCH v4] " Tri Vo
2019-07-15 21:48 ` Rafael J. Wysocki
2019-07-16 2:11 ` Greg Kroah-Hartman
2019-07-16 4:16 ` Tri Vo
2019-07-16 8:30 ` Rafael J. Wysocki
2019-07-16 8:39 ` Greg Kroah-Hartman
2019-07-16 9:36 ` Rafael J. Wysocki
2019-07-15 21:48 ` [PATCH v3] " Tri Vo
2019-07-16 2:12 ` Greg KH
2019-06-27 22:57 ` [PATCH] " Tri Vo
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