[3.19.y-ckt stable] Patch "vfs: Avoid softlockups with sendfile(2)" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    vfs: Avoid softlockups with sendfile(2)

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 1cf1db2ce2cb0d996634453e6993779664a3ac8a Mon Sep 17 00:00:00 2001
From: Jan Kara <jack at suse.cz>
Date: Mon, 23 Nov 2015 13:09:51 +0100
Subject: vfs: Avoid softlockups with sendfile(2)

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 at google.com>
Signed-off-by: Jan Kara <jack at suse.cz>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 fs/splice.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/splice.c b/fs/splice.c
index d934f8e4..c4b93e4 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -888,6 +888,7 @@ 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);
--
1.9.1