linux-kernel - [PATCH 3.4 055/125] vfs: Avoid softlockups with sendfile(2)

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Message-Id: <1476275641-4697-55-git-send-email-lizf@kernel.org>
Date:   Wed, 12 Oct 2016 20:32:51 +0800
From:   lizf@...nel.org
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>,
        Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 055/125] vfs: Avoid softlockups with sendfile(2)

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

3.4.113-rc1 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: Zefan Li <lizefan@...wei.com>
---
 fs/splice.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/splice.c b/fs/splice.c
index 4e2309e..8b97331 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -935,6 +935,7 @@ 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