The patch titled
Subject: vfs: make sendfile(2) killable even better
has been added to the -mm tree. Its filename is
vfs-make-sendfile2-killable-even-better.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vfs-make-sendfile2-killable-even-better.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vfs-make-sendfile2-killable-even-better.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: vfs: make sendfile(2) killable even better
Commit 296291cdd162 ("mm: make sendfile(2) killable") fixed an issue where
sendfile(2) was doing a lot of tiny writes into a filesystem and thus was
unkillable for a long time. However sendfile(2) can be (mis)used to issue
lots of writes into arbitrary file descriptor such as eventfd or similar
special file descriptors which never hit the standard filesystem write
path and thus are still unkillable. E.g. the following example from
Dmitry burns CPU for ~16s on my test system without possibility to be
killed:
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);
There are actually quite a few tests for pending signals in sendfile code
however when data to write is always available none of them seems to
trigger. So fix the problem by adding a test for pending signal into
splice_from_pipe_next() also before the loop waiting for pipe buffers to
be available. This should fix all the lockup issues with sendfile of the
do-ton-of-tiny-writes nature.
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/splice.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN fs/splice.c~vfs-make-sendfile2-killable-even-better fs/splice.c
--- a/fs/splice.c~vfs-make-sendfile2-killable-even-better
+++ a/fs/splice.c
@@ -809,6 +809,13 @@ static int splice_from_pipe_feed(struct
*/
static int splice_from_pipe_next(struct pipe_inode_info *pipe, struct splice_desc *sd)
{
+ /*
+ * Check for signal early to make process killable when there are
+ * always buffers available
+ */
+ if (signal_pending(current))
+ return -ERESTARTSYS;
+
while (!pipe->nrbufs) {
if (!pipe->writers)
return 0;
_
Patches currently in -mm which might be from jack@xxxxxxx are
vfs-make-sendfile2-killable-even-better.patch
vfs-avoid-softlockups-with-sendfile2.patch
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