linux-kernel - [PATCH 3.12 058/116] vfs: Avoid softlockups with sendfile(2)

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Date:	Fri,  4 Mar 2016 10:01:43 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 058/116] vfs: Avoid softlockups with sendfile(2)

From: Jan Kara <jack@...e.cz>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit c2489e07c0a71a56fb2c84bc0ee66cddfca7d068 upstream.

The following test program from Dmitry can cause softlockups or RCU
stalls as it copies 1GB from tmpfs into eventfd and we don't have any
scheduling point at that path in sendfile(2) implementation:

        int r1 = eventfd(0, 0);
        int r2 = memfd_create("", 0);
        unsigned long n = 1<<30;
        fallocate(r2, 0, 0, n);
        sendfile(r1, r2, 0, n);

Add cond_resched() into __splice_from_pipe() to fix the problem.

CC: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/splice.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/splice.c b/fs/splice.c
index 76cb3a0b1ec4..76cbc01df6a4 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -949,6 +949,7 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
 
 	splice_from_pipe_begin(sd);
 	do {
+		cond_resched();
 		ret = splice_from_pipe_next(pipe, sd);
 		if (ret > 0)
 			ret = splice_from_pipe_feed(pipe, sd, actor);
-- 
2.7.2