Re: [PATCH v5 04/46] pwm: get rid of pwm->lock

Thierry Reding
2016-04-12T11:22:56Z

[-- Attachment #1: Type: text/plain, Size: 1195 bytes --]

On Wed, Mar 30, 2016 at 10:03:27PM +0200, Boris Brezillon wrote:
> PWM devices are not protected against concurrent accesses. The lock in
> pwm_device might let PWM users think it is, but it's actually only
> protecting the enabled state.
>
> Removing this lock should be fine as long as all PWM users are aware that
> accesses to the PWM device have to be serialized, which seems to be the
> case for all of them except the sysfs interface.
> Patch the sysfs code by adding a lock to the pwm_export struct and making
> sure it's taken for all accesses to the exported PWM device.
>
> Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> ---
> drivers/pwm/core.c | 19 ++++--------------
> drivers/pwm/sysfs.c | 57 ++++++++++++++++++++++++++++++++++++++++++-----------
> include/linux/pwm.h | 2 --
> 3 files changed, 50 insertions(+), 28 deletions(-)

This is a little overzealous. Only accesses that can cause races need to
be protected by the lock. All of the *_show() callbacks don't modify the
PWM device in any way, so there is no need to protect them against
concurrent accesses.

I've dropped the changes when applying.

Thanks,
Thierry

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 819 bytes --]