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Bug#769935: marked as done (linux: Please backport nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait)

Your message dated Sun, 01 Mar 2015 05:48:40 +0000
with message-id <1425188920.28544.118.camel@decadent.org.uk>
and subject line Re: linux: Please backport nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait
has caused the Debian Bug report #769935,
regarding linux: Please backport nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
769935: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=769935
Debian Bug Tracking System
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--- Begin Message --- 
Source: linux
Version: 3.16.7-2
Severity: important
Tags: upstream patch

Dear Maintainer,

in certain circumstances, the kernel may busy-wait indefinitely after
processing a SIGKILL to a process when using NFS. There is a patch for this 
issue that went into 3.17:

<http://www.spinics.net/lists/linux-nfs/msg45807.html>
<https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=92a56555bd576c61b27a5cab9f38a33a1e9a1df5>
I've attached a backported version of the patch for this (the original patch 
does not directly apply due to another commit [1] in 3.17).

I've tested that the patch applies (against 3.16.7-2), the modified
package compiles and that the resulting kernel boots (with no obvious
regressions). I haven't seen any busy-waits with that since, but the
bug is not trivial to trigger.

Thanks!

Christian
[1] <https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c1221321b7c25b53204447cff9949a6d5a7ddddc> 
From 92a56555bd576c61b27a5cab9f38a33a1e9a1df5 Mon Sep 17 00:00:00 2001
From: David Jeffery <djeffery@redhat.com>
Date: Tue, 5 Aug 2014 11:19:42 -0400
Subject: nfs: Don't busy-wait on SIGKILL in __nfs_iocounter_wait

If a SIGKILL is sent to a task waiting in __nfs_iocounter_wait,
it will busy-wait or soft lockup in its while loop.
nfs_wait_bit_killable won't sleep, and the loop won't exit on
the error return.

Stop the busy-wait by breaking out of the loop when
nfs_wait_bit_killable returns an error.

Signed-off-by: David Jeffery <djeffery@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 932c6cc..be7cbce 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -116,7 +116,7 @@ __nfs_iocounter_wait(struct nfs_io_counter *c)
 		if (atomic_read(&c->io_count) == 0)
 			break;
 		ret = nfs_wait_bit_killable(&c->flags);
-	} while (atomic_read(&c->io_count) != 0);
+	} while (atomic_read(&c->io_count) != 0 && !ret);
 	finish_wait(wq, &q.wait);
 	return ret;
 }
-- 
cgit v0.10.1

--- End Message ---
--- Begin Message --- 
Version: 3.16.7-ckt4-1

On Mon, 17 Nov 2014 19:34:40 +0100 Christian Seiler <christian@iwakd.de> wrote:
> Source: linux
> Version: 3.16.7-2
> Severity: important
> Tags: upstream patch
> 
> Dear Maintainer,
> 
> in certain circumstances, the kernel may busy-wait indefinitely after
> processing a SIGKILL to a process when using NFS. There is a patch for 
> this
> issue that went into 3.17:
> 
> <http://www.spinics.net/lists/linux-nfs/msg45807.html>
> <https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=92a56555bd576c61b27a5cab9f38a33a1e9a1df5>
> 
> I've attached a backported version of the patch for this (the original 
> patch
> does not directly apply due to another commit [1] in 3.17).
> 
> I've tested that the patch applies (against 3.16.7-2), the modified
> package compiles and that the resulting kernel boots (with no obvious
> regressions). I haven't seen any busy-waits with that since, but the
> bug is not trivial to trigger.

This patch was included in 3.16.7-ckt3.

Ben.


-- 
Ben Hutchings
Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer

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