From: Oliver Neukum <oneukum@suse.com>
To: Douglas Anderson <dianders@chromium.org>
Cc: groeck@chromium.org, grundler@chromium.org,
linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
netdev@vger.kernel.org
Subject: Re: [RFC PATCH 2/3] usbnet: Avoid potential races in usbnet_deferred_kevent()
Date: Tue, 19 Sep 2017 22:37:56 +0200 [thread overview]
Message-ID: <1505853476.15836.9.camel@suse.com> (raw)
In-Reply-To: <20170919161522.995-2-dianders@chromium.org>
Am Dienstag, den 19.09.2017, 09:15 -0700 schrieb Douglas Anderson:
> In general when you've got a flag communicating that "something needs
> to be done" you want to clear that flag _before_ doing the task. If
> you clear the flag _after_ doing the task you end up with the risk
> that this will happen:
>
> 1. Requester sets flag saying task A needs to be done.
> 2. Worker comes and stars doing task A.
> 3. Worker finishes task A but hasn't yet cleared the flag.
> 4. Requester wants to set flag saying task A needs to be done again.
> 5. Worker clears the flag without doing anything.
>
> Let's make the usbnet codebase consistently clear the flag _before_ it
> does the requested work. That way if there's another request to do
> the work while the work is already in progress it won't be lost.
>
> NOTES:
> - No known bugs are fixed by this; it's just found by code inspection.
Hi,
unfortunately the patch is wrong. The flags must be cleared only
in case the handler is successful. That is not guaranteed.
Regards
Oliver
NACK
next prev parent reply other threads:[~2017-09-19 20:37 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-19 16:15 [RFC PATCH 1/3] usbnet: Get rid of spammy usbnet "kevent X may have been dropped" Douglas Anderson
2017-09-19 16:15 ` [RFC PATCH 2/3] usbnet: Avoid potential races in usbnet_deferred_kevent() Douglas Anderson
2017-09-19 20:37 ` Oliver Neukum [this message]
2017-09-19 20:51 ` Guenter Roeck
2017-09-20 8:23 ` Oliver Neukum
2017-09-19 20:53 ` Doug Anderson
2017-09-20 8:25 ` Oliver Neukum
2017-09-19 16:15 ` [RFC PATCH 3/3] usbnet: Fix memory leak when rx_submit() fails Douglas Anderson
2017-09-19 17:41 ` Bjørn Mork
2017-09-19 16:43 ` [RFC PATCH 1/3] usbnet: Get rid of spammy usbnet "kevent X may have been dropped" Guenter Roeck
2017-09-19 17:45 ` Bjørn Mork
2017-09-19 20:36 ` Oliver Neukum
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