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

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Message-ID: <8760ze99dv.fsf@gmail.com>
Date:	Thu, 31 Dec 2015 11:53:48 +0100
From:	Nicolai Stange <nicstange@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	nicstange@...il.com, edumazet@...gle.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net, socket, socket_wq: fix missing initialization of flags

David Miller <davem@...emloft.net> writes:

> From: Nicolai Stange <nicstange@...il.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@...il.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@...il.com>

Thank you very much!

Regarding the correct position of the "Fixes:" tag: lesson learned.
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