From: Al Viro <viro@ZenIV•linux.org.uk>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org, xiyou.wangcong@gmail•com
Subject: Re: "af_unix: conditionally use freezable blocking calls in read" is wrong
Date: Mon, 5 Dec 2016 03:52:41 +0000 [thread overview]
Message-ID: <20161205035241.GJ1555@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20161204.214214.1868750446620130834.davem@davemloft.net>
On Sun, Dec 04, 2016 at 09:42:14PM -0500, David Miller wrote:
> > I've run into that converting AF_UNIX to generic_file_splice_read();
> > I can kludge around that ("freezable unless ->msg_iter is ITER_PIPE"), but
> > that only delays trouble.
> >
> > Note that the only other user of freezable_schedule_timeout() is
> > a very different story - it's a kernel thread, which *does* have a guaranteed
> > locking environment. Making such assumptions in unix_stream_recvmsg(),
> > OTOH, is insane...
>
> We have to otherwise Android phones drain their batteries in 10
> minutes.
>
> I'm not going to revert this and be responsible for that.
>
> So you have to find a way to make the freezable calls legitimate.
Oh, well... As I said, I can kludge around that - call from
generic_file_splice_read() can be distinguished by looking at the
->msg_iter->type; it still means unpleasantness for kernel_recvmsg()
users - in effect, it can only be called with locks held if you know that
the socket is not an AF_UNIX one.
BTW, how do they deal with plain pipes?
next prev parent reply other threads:[~2016-12-05 3:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-04 21:04 "af_unix: conditionally use freezable blocking calls in read" is wrong Al Viro
2016-12-05 2:42 ` David Miller
2016-12-05 3:52 ` Al Viro [this message]
2016-12-06 4:24 ` Cong Wang
2016-12-06 18:37 ` Colin Cross
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