From: "Henrik Rydberg" <rydberg@euromail.se>
To: Jeffrey Brown <jeffbrown@android.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
djkurtz@google.com, linux-input@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/4] input: evdev: Make device readable only when it contains a complete packet.
Date: Tue, 5 Apr 2011 14:03:27 +0200 [thread overview]
Message-ID: <20110405120327.GA19300@polaris.bitmath.org> (raw)
In-Reply-To: <BANLkTinLcXsZpHm3_uzRUEdrJQsbozgghA@mail.gmail.com>
> >> Should use client->head here so that the SYN_DROPPED is readable.
> >
> > It is readable, but we do not want to signal on it.
>
> I think we do want to signal on it. We should signal whenever the
> device becomes readable.
>
> Signaling on dropped is useful in the case where a misbehaving device
> driver fails to ever call input_sync. If that happens, we might
> enqueue a dropped event and then never wake up the client which makes
> the issue hard to diagnose.
A device that never wakes up the client seems like a detectable
symptom. I agree with Dmitry, the dropped event is more of a note in
passing, and as such can stay in the pipe until a real EV_SYN event
comes along.
> >> I don't think it's safe to modify last_syn outside of the spin lock.
> >> This should be done above.
> >
> > This is the only writer, plus we are running under event_lock with
> > interrupts off, so it is safe.
>
> The value will be read concurrently by evdev_fetch_next_event. So if
> this were safe, then we wouldn't need the spin lock at all.
The spinlock ensures atomic read/write of the event buffer. The
position into the buffer does not need the lock.
> At the very least for the sake of consistency, I think we should keep
> the buffer manipulations within the guarded region.
Sounds reasonable.
Thanks,
Henrik
next prev parent reply other threads:[~2011-04-05 12:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-02 6:54 [PATCH v2 1/4] input: Set default events per packet Jeff Brown
2011-04-02 6:54 ` [PATCH v2 2/4] hid: hid-input: Remove obsolete default events per packet setting Jeff Brown
2011-04-05 12:20 ` Henrik Rydberg
2011-04-02 6:54 ` [PATCH v2 3/4] input: evdev: Indicate buffer overrun with SYN_DROPPED Jeff Brown
2011-04-04 21:33 ` Dmitry Torokhov
2011-04-04 21:52 ` Jeffrey Brown
2011-04-05 11:41 ` Henrik Rydberg
2011-04-02 6:54 ` [PATCH v2 4/4] input: evdev: Make device readable only when it contains a complete packet Jeff Brown
2011-04-04 21:36 ` Dmitry Torokhov
2011-04-04 22:16 ` Jeffrey Brown
2011-04-04 22:46 ` Dmitry Torokhov
2011-04-05 0:34 ` Jeffrey Brown
2011-04-05 12:03 ` Henrik Rydberg [this message]
2011-04-05 16:32 ` Dmitry Torokhov
2011-04-05 16:38 ` Dmitry Torokhov
2011-04-11 20:15 ` Jeffrey Brown
2011-04-05 12:16 ` [PATCH v2 1/4] input: Set default events per packet Henrik Rydberg
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