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?
