linux-kernel - Re: [PATCH 5.19 0191/1157] hwmon: (sht15) Fix wrong assumptions in device remove callback

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Date:   Sun, 21 Aug 2022 10:05:55 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.19 0191/1157] hwmon: (sht15) Fix wrong assumptions in
 device remove callback

On Sat, Aug 20, 2022 at 08:14:42PM +0200, Greg Kroah-Hartman wrote:
> On Fri, Aug 19, 2022 at 09:35:01PM +0200, Uwe Kleine-König wrote:
> > Hello Greg,
> > 
> > On Tue, Aug 16, 2022 at 12:40:50PM +0200, Greg Kroah-Hartman wrote:
> > > On Mon, Aug 15, 2022 at 11:49:11PM +0200, Uwe Kleine-König wrote:
> > > > On Mon, Aug 15, 2022 at 07:52:27PM +0200, Greg Kroah-Hartman wrote:
> > > > > From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > > > 
> > > > > [ Upstream commit 7d4edccc9bbfe1dcdff641343f7b0c6763fbe774 ]
> > > > > 
> > > > > Taking a lock at the beginning of .remove() doesn't prevent new readers.
> > > > > With the existing approach it can happen, that a read occurs just when
> > > > > the lock was taken blocking the reader until the lock is released at the
> > > > > end of the remove callback which then accessed *data that is already
> > > > > freed then.
> > > > > 
> > > > > To actually fix this problem the hwmon core needs some adaption. Until
> > > > > this is implemented take the optimistic approach of assuming that all
> > > > > readers are gone after hwmon_device_unregister() and
> > > > > sysfs_remove_group() as most other drivers do. (And once the core
> > > > > implements that, taking the lock would deadlock.)
> > > > > 
> > > > > So drop the lock, move the reset to after device unregistration to keep
> > > > > the device in a workable state until it's deregistered. Also add a error
> > > > > message in case the reset fails and return 0 anyhow. (Returning an error
> > > > > code, doesn't stop the platform device unregistration and only results
> > > > > in a little helpful error message before the devm cleanup handlers are
> > > > > called.)
> > > > > 
> > > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > > > Link: https://lore.kernel.org/r/20220725194344.150098-1-u.kleine-koenig@pengutronix.de
> > > > > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> > > > > Signed-off-by: Sasha Levin <sashal@...nel.org>
> > > > 
> > > > Does this mean my concerns I expressed in the mail with Message-Id:
> > > > 20220814155638.idxnihylofsxqlql@...gutronix.de were not taken into
> > > > consideration?
> > > 
> > > I can't find that message-id on lore.kernel.org, do you have a link?
> > 
> > Oh, I missed your request earlier. No I don't have a link, the mail was
> > sent to Sasha Levin, Jean Delvare, Guenter Roeck and stable-commits as I
> > just replied to the "note to let you know that I've just added the patch
> > titled [...] to the 5.19-stable tree".
> 
> Ok, I've dropped it now from all pending queues (5.10 and older), I can
> also revert it from the newer ones if you want me to.

Actually I don't care much. It touches a path that is not usually hit,
because platform devices are not removed very often. So I expect even if
the problem with this driver is a different one now, we won't get any
regressions here.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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