On Thu, Nov 17, 2016 at 2:30 PM, Colin Cross <ccr...@android.com> wrote:
> On Thu, Nov 17, 2016 at 2:09 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
>> Commit 2b15af6f95 ("af_unix: use freezable blocking calls in read")
>> converts schedule_timeout() to its freezable version, it was probably
>> correct at that time, but later, commit 2b514574f7e8
>> ("net: af_unix: implement splice for stream af_unix sockets") breaks
>> the strong requirement for a freezable sleep, according to
>> commit 0f9548ca1091:
>>
>> We shouldn't try_to_freeze if locks are held. Holding a lock can cause a
>> deadlock if the lock is later acquired in the suspend or hibernate path
>> (e.g. by dpm). Holding a lock can also cause a deadlock in the case of
>> cgroup_freezer if a lock is held inside a frozen cgroup that is later
>> acquired by a process outside that group.
>>
>> The pipe_lock is still held at that point. So just revert commit 2b15af6f95.
>
> On my phone 77 threads are blocked in unix_stream_recvmsg. A simple
> revert of this patch will cause every one of those threads to wake up
> twice per suspend cycle, which can be multiple times a second. How
> about adding a freezable flag to unix_stream_read_state so
> unix_stream_recvmsg can stay freezable, and unix_stream_splice_read
> can be unfreezable?
Fair enough, I didn't know it could have such an impact.
I will send v2.
Thanks.
