From: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Mark Brown <broonie@kernel.org>,
Liam Girdwood <lgirdwood@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: regulator: deadlock vs memory reclaim
Date: Tue, 11 Aug 2020 02:07:22 +0200 [thread overview]
Message-ID: <20200811000722.GA30574@qmqm.qmqm.pl> (raw)
In-Reply-To: <81e490af-d1da-873a-51b4-130ca82fd1f6@gmail.com>
On Mon, Aug 10, 2020 at 11:56:13PM +0300, Dmitry Osipenko wrote:
> 10.08.2020 23:21, Dmitry Osipenko пишет:
> > 10.08.2020 23:18, Michał Mirosław пишет:
> >> On Mon, Aug 10, 2020 at 11:15:28PM +0300, Dmitry Osipenko wrote:
> >>> 10.08.2020 23:09, Michał Mirosław пишет:
> >>>> At first I also thought so, but there's more. Below is a lockdep
> >>>> complaint with your patch applied. I did a similar patch and then two more
> >>>> (following) and that is still not enough (sysfs/debugfs do allocations,
> >>>> too).
> >>> Then it should be good to move the locking for init_coupling() like I
> >>> suggested and use GFP_NOWAIT for the two other cases. It all could be a
> >>> single small patch. Could you please check whether GFP_NOWAIT helps?
> >>
> >> This would be equivalent to my patches. Problem with sysfs and debugfs
> >> remains as they don't have the option of GFP_NOWAIT. This needs to be
> >> moved outside of the locks.
> >
> > Ah okay, you meant the debugfs core. I see now, thanks.
> >
>
> This indeed needs a capital solution.
>
> It's not obvious how to fix it.. we can probably remove taking the
> list_mutex from lock_dependent(), but this still won't help the case of
> memory reclaiming because reclaim may cause touching the already locked
> regulator. IIUC, the case of memory reclaiming under regulator lock was
> always dangerous and happened to work by chance before, correct?
I just noticed that locking in regulator_resolve_coupling() is bogus.
This all holds up because regulator_list_mutex is held during the call.
Feel free to test a patch below.
I'm working my way to push allocations outside of the locks, but the
coupling-related locking will need to be fixed regardless.
Best Regards,
Michał Mirosław
---->8<----
[PATCH] regulator: remove superfluous lock in regulator_resolve_coupling()
The code modifies rdev, but locks c_rdev instead. The bug remains:
stored c_rdev could be freed just after unlock anyway. This doesn't blow
up because regulator_list_mutex taken outside holds it together.
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
---
drivers/regulator/core.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 94f9225869da..e519bc9a860d 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -4859,13 +4859,9 @@ static void regulator_resolve_coupling(struct regulator_dev *rdev)
return;
}
- regulator_lock(c_rdev);
-
c_desc->coupled_rdevs[i] = c_rdev;
c_desc->n_resolved++;
- regulator_unlock(c_rdev);
-
regulator_resolve_coupling(c_rdev);
}
}
--
2.20.1
next prev parent reply other threads:[~2020-08-11 0:07 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1597089543.git.mirq-linux@rere.qmqm.pl>
2020-08-10 20:09 ` [RFC PATCH 1/3] regulator: allocate memory outside of regulator_list mutex Michał Mirosław
2020-08-10 20:09 ` [RFC PATCH 2/3] regulator: push enable_gpio allocation out from under regulator_list_mutex Michał Mirosław
2020-08-10 20:09 ` [RFC PATCH 3/3] regulator: push supply_name allocation outside of lock Michał Mirosław
2020-08-10 20:15 ` regulator: deadlock vs memory reclaim Dmitry Osipenko
2020-08-10 20:18 ` Michał Mirosław
2020-08-10 20:21 ` Dmitry Osipenko
2020-08-10 20:56 ` Dmitry Osipenko
2020-08-10 21:23 ` Dmitry Osipenko
2020-08-11 0:07 ` Michał Mirosław [this message]
2020-08-11 15:44 ` Dmitry Osipenko
2020-08-09 22:25 Michał Mirosław
2020-08-10 0:09 ` Dmitry Osipenko
2020-08-10 15:39 ` Mark Brown
2020-08-10 16:09 ` Michał Mirosław
2020-08-10 17:31 ` Mark Brown
2020-08-10 19:25 ` Michał Mirosław
2020-08-10 19:41 ` Dmitry Osipenko
2020-08-10 19:51 ` Mark Brown
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