Re: [Drbd-dev] [PATCH] drbd: fix regression 'out of mem, failed to invoke fence-peer helper'

[Lars Ellenberg <lars.ellenberg@linbit.com>]

On Sun, Oct 05, 2014 at 04:47:01PM -0700, Greg KH wrote:
> On Wed, Oct 01, 2014 at 11:32:29AM +0200, Philipp Reisner wrote:
> > From: Lars Ellenberg <lars.ellenberg@linbit.com>
> > 
> > Stable info:
> >   This patch landed in upstream with v3.16 as commit
> >   bbc1c5e8ad6dfebf9d13b8a4ccdf66c92913eac9
> >   it should go into v3.14+
> > 
> > Since linux kernel 3.13, kthread_run() internally uses
> > wait_for_completion_killable().  We sometimes may use kthread_run()
> > while we still have a signal pending, which we used to kick our threads
> > out of potentially blocking network functions, causing kthread_run() to
> > mistake that as a new fatal signal and fail.
> > 
> > Fix: flush_signals() before kthread_run().
> > 
> > Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
> > Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
> > Signed-off-by: Jens Axboe <axboe@fb.com>
> > ---
> >  drivers/block/drbd/drbd_nl.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> > index 1b35c45..3f2e167 100644
> > --- a/drivers/block/drbd/drbd_nl.c
> > +++ b/drivers/block/drbd/drbd_nl.c
> > @@ -544,6 +544,12 @@ void conn_try_outdate_peer_async(struct drbd_connection *connection)
> >         struct task_struct *opa;
> > 
> >         kref_get(&connection->kref);
> > +       /* We may just have force_sig()'ed this thread
> > +        * to get it out of some blocking network function.
> > +        * Clear signals; otherwise kthread_run(), which internally uses
> > +        * wait_on_completion_killable(), will mistake our pending signal
> > +        * for a new fatal signal and fail. */
> > +       flush_signals(current);
> >         opa = kthread_run(_try_outdate_peer_async, connection, "drbd_async_h");
> >         if (IS_ERR(opa)) {
> >                 drbd_err(connection, "out of mem, failed to invoke fence-peer helper\n");
> 
> This doesn't apply to 3.16-stable or 3.14-stable, can you please provide
> a working backport?

There was a rename of "tconn" to "connection" between 3.14 and .15.
Other than that, this has not changed.
Below applies to 3.13 and 3.14 stable as of today.

	Lars

8<----

From a82efa2adeb992b5ded798b01b4567bc07b6ab1b Mon Sep 17 00:00:00 2001
From: Lars Ellenberg <lars.ellenberg@linbit.com>
Date: Tue, 7 Oct 2014 17:20:27 +0200
Subject: [PATCH] drbd: fix regression 'out of mem, failed to invoke fence-peer
 helper'

Stable info:
  This patch landed in upstream with v3.16 as commit
  bbc1c5e8ad6dfebf9d13b8a4ccdf66c92913eac9
  it should go into v3.13+

Since linux kernel 3.13, kthread_run() internally uses
wait_for_completion_killable().  We sometimes may use kthread_run()
while we still have a signal pending, which we used to kick our threads
out of potentially blocking network functions, causing kthread_run() to
mistake that as a new fatal signal and fail.

Fix: flush_signals() before kthread_run().

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
---
 drivers/block/drbd/drbd_nl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index c706d50..8c16c2f 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -525,6 +525,12 @@ void conn_try_outdate_peer_async(struct drbd_tconn *tconn)
 	struct task_struct *opa;
 
 	kref_get(&tconn->kref);
+	/* We may just have force_sig()'ed this thread
+	 * to get it out of some blocking network function.
+	 * Clear signals; otherwise kthread_run(), which internally uses
+	 * wait_on_completion_killable(), will mistake our pending signal
+	 * for a new fatal signal and fail. */
+	flush_signals(current);
 	opa = kthread_run(_try_outdate_peer_async, tconn, "drbd_async_h");
 	if (IS_ERR(opa)) {
 		conn_err(tconn, "out of mem, failed to invoke fence-peer helper\n");
-- 
1.9.1