Re: [PATCH 2/5] echoaudio: Race conditions around "opencount"

On Wed, 08 Jul 2020 12:18:45 +0200, Mark Hills wrote:

Use of atomics does not make these statements robust:

   atomic_inc(&chip->opencount);
   if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
           chip->can_set_rate=0;

and

   if (atomic_read(&chip->opencount)) {
           if (chip->opencount) {
                   changed = -EAGAIN;
           } else {
                   changed = set_digital_mode(chip, dmode);

It would be necessary to atomically increment or decrement the value and use the returned result. And yet we still need to prevent other threads making use of "can_set_rate" while we set it.

However in all but one case the atomic is misleading as they are already running with "mode_mutex" held.

Decisions are made on mode setting are often intrinsically connected to "opencount" because some operations are not permitted unless there is sole ownership.

So instead simplify this, and use "mode_mutex" as a lock for all reference counting and mode setting.

Signed-off-by: Mark Hills mark@xwax.org

Applied now. Thanks.

Takashi