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@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 47ae562efbd0fd8440959304915291865b945c67)
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/fs/splice.c b/fs/splice.c
index 5c006c8bba5d0cf454fc69d6a0be4b90a37e4d14..9618feb947ca97f270a2426304e27cc5f421578d 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -882,6 +882,7 @@ 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);