Re: [PATCH v2] net, socket, socket_wq: fix missing initialization of flags

[David Miller <davem@davemloft.net>]

From: Nicolai Stange <nicstange@gmail.com>
Date: Tue, 29 Dec 2015 13:29:55 +0100

> Fixes: ceb5d58b2170 ("net: fix sock_wake_async() rcu protection")
> 
> Commit ceb5d58b2170 ("net: fix sock_wake_async() rcu protection") from
> the current 4.4 release cycle introduced a new flags member in
> struct socket_wq and moved SOCKWQ_ASYNC_NOSPACE and SOCKWQ_ASYNC_WAITDATA
> from struct socket's flags member into that new place.
> 
> Unfortunately, the new flags field is never initialized properly, at least
> not for the struct socket_wq instance created in sock_alloc_inode().
> 
> One particular issue I encountered because of this is that my GNU Emacs
> failed to draw anything on my desktop -- i.e. what I got is a transparent
> window, including the title bar. Bisection lead to the commit mentioned
> above and further investigation by means of strace told me that Emacs
> is indeed speaking to my Xorg through an O_ASYNC AF_UNIX socket. This is
> reproducible 100% of times and the fact that properly initializing the
> struct socket_wq ->flags fixes the issue leads me to the conclusion that
> somehow SOCKWQ_ASYNC_WAITDATA got set in the uninitialized ->flags,
> preventing my Emacs from receiving any SIGIO's due to data becoming
> available and it got stuck.
> 
> Make sock_alloc_inode() set the newly created struct socket_wq's ->flags
> member to zero.
> 
> Signed-off-by: Nicolai Stange <nicstange@gmail.com>

Applied, but please in the future please put the Fixes: tag right
above the first signoff/ack, like this:

Fixes: ceb5d58b2170 ("net: fix sock_wake_async() rcu protection")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>