[1/2] vfs: Make sendfile(2) killable even better
diff mbox

Message ID 1448280591-27867-1-git-send-email-jack@suse.cz
State New
Headers show

Commit Message

Jan Kara Nov. 23, 2015, 12:09 p.m. UTC
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 evenfd 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 we 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.

CC: stable@vger.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/splice.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Dmitry Vyukov Nov. 23, 2015, 7:42 p.m. UTC | #1
Fixed the issue for me.

Tested-by: Dmitry Vyukov <dvyukov@google.com>

Thanks for quick fixes!


On Mon, Nov 23, 2015 at 1:09 PM, Jan Kara <jack@suse.cz> wrote:
> 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 evenfd 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 we 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.
>
> CC: stable@vger.kernel.org
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/splice.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/fs/splice.c b/fs/splice.c
> index 801c21cd77fe..22adbbe51e52 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -809,6 +809,13 @@ static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
>   */
>  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;
> --
> 2.1.4
>
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Patch
diff mbox

diff --git a/fs/splice.c b/fs/splice.c
index 801c21cd77fe..22adbbe51e52 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -809,6 +809,13 @@  static int splice_from_pipe_feed(struct pipe_inode_info *pipe, struct splice_des
  */
 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;