linux-kernel - Re: regulator: deadlock vs memory reclaim

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <d6b4ec96-d81b-5025-628b-ba6c5f77a3dc@gmail.com>
Date:   Tue, 11 Aug 2020 18:44:09 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: regulator: deadlock vs memory reclaim

11.08.2020 03:07, Michał Mirosław пишет:
...
> 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@...e.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);
>  	}
>  }
> 

The change looks like a good cleanup to me, thanks. I think that c_rdev
locking was accidentally left from some older version of the patch that
introduced the coupling support. There shouldn't be any real bug in this
code.

IIRC, at some point I changed the code to disallow consumers to get a
partially coupled regulator and then protected the resolve_coupling()
with list_mutex, but seems missed to remove that c_rdev locking. Hence
there shouldn't be a need to lock regulators individually during the
resolve because nothing should touch the coupled regulators until all
the coupling has been resolved.