[alsa-devel] [PATCH 0/5] ALSA: control: fix issue of concurrent access for TLV operations

[Takashi Sakamoto]

Hi,

On 2017年08月04日 23:52, Takashi Iwai wrote:
> On Thu, 03 Aug 2017 13:20:39 +0200,
> Takashi Sakamoto wrote:
>>
>> Hi,
>>
>> In a design of ALSA control core, each set of elements have data of
>> Type-Length-Value shape. This is called as TLV data. In ALSA control
>> interface, applications can three types of requests to elements about
>> TLV data; read, write and command.
>>
>> In current implementation of ALSA control core, these three requests
>> are handled with read lock of a counting semaphore. However, this has an
>> issue of concurrent access because in theory write/command requests have
>> sub-effects to change state of the set of elements in a point of TLV data.
>> Read requests and write/command requests are handled exclusively as well
>> as each write/command requests.
>>
>> This patchset is for this purpose. Additionally, this applies code
>> refactoring to TLV ioctl handler and TLV handler for user-defined element
>> set so that they get better shape for readers.
> 
> Taking the rw mutex outside snd_ctl_tlv_ioctl() is a good idea.
> It simplified things a lot, indeed.
> 
> Now applied all patches.  Thanks!

Thanks. But I found that commit 30d8340b5857 ("ALSA: control: obsolete 
user_ctl_lock") brought another concurrent access issue between 
ELEM_READ/ELEM_WRITE for user-defined element sets, due to a generic bug 
in handlers of these two requests in ALSA control core. I pushed my 
commits into my repository to fix this. The latest three commits.
https://github.com/takaswie/sound/commits/topic/fix-ctl-writelock

I'll post them after enough tests.


Thanks

Takashi Sakamoto