On Sun, 2015-12-27 at 21:00 +0100, Nicolai Stange wrote:
> 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 introduces 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_NOSPACE got set in the uninitialized ->flags,
> preventing my Emacs from receiving any SIGIO's due to send space becoming
> available again 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 <nicsta...@gmail.com>
> ---
> net/socket.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/socket.c b/net/socket.c
> index 29822d6..d730ef9 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -257,6 +257,7 @@ static struct inode *sock_alloc_inode(struct super_block
> *sb)
> }
> init_waitqueue_head(&wq->wait);
> wq->fasync_list = NULL;
> + wq->flags = 0;
> RCU_INIT_POINTER(ei->socket.wq, wq);
>
> ei->socket.state = SS_UNCONNECTED;
Thanks a lot Nicolai for finding this.
I completely overlooked this initial value.
I checked other places where 'struct socket_wq' were allocated and they
look fine.
Acked-by: Eric Dumazet <eduma...@google.com>
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
