linux-kernel - Re: [PATCH] i2c: s3c2410: fix ABBA deadlock by keeping clock prepared

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

Message-ID: <CAJKOXPfTwkx7A6tjMaANuafsFonAunDv4CV+QPgF6SKbRZ4mzQ@mail.gmail.com>
Date:	Fri, 23 Jan 2015 09:58:16 +0100
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Paul Osmialowski <p.osmialowsk@...sung.com>
Cc:	Kukjin Kim <kgene@...nel.org>, Wolfram Sang <wsa@...-dreams.de>,
	Mark Brown <broonie@...nel.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	linux-samsung-soc@...r.kernel.org, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH] i2c: s3c2410: fix ABBA deadlock by keeping clock prepared

2015-01-19 17:03 GMT+01:00 Paul Osmialowski <p.osmialowsk@...sung.com>:
> This patch solves deadlock between clock prepare mutex and regmap mutex reported
> by Tomasz Figa in [1] by implementing solution from [2]: "always leave the clock
> of the i2c controller in a prepared state".
>
> [1] https://lkml.org/lkml/2014/7/2/171
> [2] https://lkml.org/lkml/2014/7/2/207
>
> On each i2c transfer handled by s3c24xx_i2c_xfer(), clk_prepare_enable() was
> called, which calls clk_prepare() then clk_enable(). clk_prepare() takes
> prepare_lock mutex before proceeding. Note that i2c transfer functions are
> invoked from many places in kernel, typically with some other additional lock
> held.
>
> It may happen that function on CPU1 (e.g. regmap_update_bits()) has taken a
> mutex (i.e. regmap lock mutex) then it attempts i2c communication in order to
> proceed (so it needs to obtain clock related prepare_lock mutex during transfer
> preparation stage due to clk_prepare() call). At the same time other task on
> CPU0 wants to operate on clock (e.g. to (un)prepare clock for some other reason)
> so it has taken prepare_lock mutex.
>
> CPU0:                        CPU1:
> clk_disable_unused()         regulator_disable()
>   clk_prepare_lock()           map->lock(map->lock_arg)
>   regmap_read()                s3c24xx_i2c_xfer()
>     map->lock(map->lock_arg)     clk_prepare_lock()
>
> Implemented solution from [2] leaves i2c clock prepared. Preparation is done in
> s3c24xx_i2c_probe() function. Without this patch, it is immediately unprepared
> by clk_disable_unprepare() call. I've replaced this call with clk_disable() and
> I've added clk_unprepare() call in s3c24xx_i2c_remove().
>
> The s3c24xx_i2c_xfer() function now uses clk_enable() instead of
> clk_prepare_enable() (and clk_disable() instead of clk_unprepare_disable()).
>
> Signed-off-by: Paul Osmialowski <p.osmialowsk@...sung.com>
> ---
>  drivers/i2c/busses/i2c-s3c2410.c | 23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)

Looks good to me.

Reviewed-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Best regards,
Krzysztof
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/