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

[Thierry Reding]

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@xxxxxxxxxxxxxxxxxx>
> ---
>  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

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