Re: [PATCH 04/12] splice: lift pipe_lock out of splice_to_pipe()

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On Sun, Dec 18, 2016 at 08:12:07PM +0000, Al Viro wrote:
> On Sun, Dec 18, 2016 at 11:28:44AM -0800, Linus Torvalds wrote:
> > On Sat, Dec 17, 2016 at 11:54 AM, Andreas Schwab <schwab@xxxxxxxxxxxxxx> wrote:
> > > This break EPIPE handling inside splice when SIGPIPE is ignored:
> > >
> > > Before:
> > > $ { sleep 1; strace -e splice pv -q /dev/zero; } | :
> > 
> > Where is that "splice" program from? Google isn't helpful, and fedora
> > doesn't seem to have it. I'm assuming it was posted in one of the
> > threads, but if so I've long since lost sight of it..
> 
> It's pv(1), actually.  I'm looking into that - debian-packaged pv reproduced
> that crap.

OK, I see what's going on - it's wait_for_space() lifted past the checks
for lack of readers.  The fix, AFAICS, is simply

diff --git a/fs/splice.c b/fs/splice.c
index 6a2b0db5..aeba2b7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1082,6 +1082,10 @@ EXPORT_SYMBOL(do_splice_direct);
 
 static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
 {
+	if (unlikely(!pipe->readers)) {
+		send_sig(SIGPIPE, current, 0);
+		return -EPIPE;
+	}
 	while (pipe->nrbufs == pipe->buffers) {
 		if (flags & SPLICE_F_NONBLOCK)
 			return -EAGAIN;
@@ -1090,6 +1094,10 @@ static int wait_for_space(struct pipe_inode_info *pipe, unsigned flags)
 		pipe->waiting_writers++;
 		pipe_wait(pipe);
 		pipe->waiting_writers--;
+		if (unlikely(!pipe->readers)) {
+			send_sig(SIGPIPE, current, 0);
+			return -EPIPE;
+		}
 	}
 	return 0;
 }
--
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