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 <redacted>
---
 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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