Messages in this thread | | | From | Cong Wang <> | Date | Thu, 17 Nov 2016 13:44:35 -0800 | Subject | Re: net: BUG still has locks held in unix_stream_splice_read |
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On Sun, Oct 9, 2016 at 8:14 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > E.g what will happen if some code does a read on AF_UNIX socket with > some local mutex held? AFAICS, there are exactly two callers of > freezable_schedule_timeout() - this one and one in XFS; the latter is > in a kernel thread where we do have good warranties about the locking > environment, but here it's in the bleeding ->recvmsg/->splice_read and > for those assumption that caller doesn't hold any locks is pretty > strong, especially since it's not documented anywhere. > > What's going on there?
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 2b514574f7e88c8498027ee366 ("net: af_unix: implement splice for stream af_unix sockets") breaks its requirement for a freezable sleep:
commit 0f9548ca10916dec166eaf74c816bded7d8e611d
lockdep: check that no locks held at freeze time
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.
So probably we just need to revert commit 2b15af6f95 now.
I am going to send a revert for at least -net and -stable, since Dmitry saw this warning again.
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