cputimer: Cure lock inversion

Fix regression introduced in 3.0.7.
Update the rt patch accordingly.

svn path=/dists/sid/linux-2.6/; revision=18171

debian/changelog

@@ -11,6 +11,9 @@ linux-2.6 (3.0.0-6) UNRELEASED; urgency=low
     For the complete list of changes, see:
      http://www.kernel.org/pub/linux/kernel/v3.0/ChangeLog-3.0.7  
 
+  [ Ben Hutchings ]
+  * cputimer: Cure lock inversion
+
  -- Uwe Kleine-König <u.kleine-koenig@pengutronix.de>  Fri, 07 Oct 2011 15:48:22 +0200
 
 linux-2.6 (3.0.0-5) unstable; urgency=low

debian/patches/bugfix/all/cputimer-Cure-lock-inversion.patch

@@ -0,0 +1,81 @@
+From: Peter Zijlstra <a.p.zijlstra@chello.nl>
+Date: Mon, 17 Oct 2011 11:50:30 +0200
+Subject: [PATCH] cputimer: Cure lock inversion
+
+commit bcd5cff7216f9b2de0a148cc355eac199dc6f1cf upstream.
+
+There's a lock inversion between the cputimer->lock and rq->lock;
+notably the two callchains involved are:
+
+ update_rlimit_cpu()
+   sighand->siglock
+   set_process_cpu_timer()
+     cpu_timer_sample_group()
+       thread_group_cputimer()
+         cputimer->lock
+         thread_group_cputime()
+           task_sched_runtime()
+             ->pi_lock
+             rq->lock
+
+ scheduler_tick()
+   rq->lock
+   task_tick_fair()
+     update_curr()
+       account_group_exec()
+         cputimer->lock
+
+Where the first one is enabling a CLOCK_PROCESS_CPUTIME_ID timer, and
+the second one is keeping up-to-date.
+
+This problem was introduced by e8abccb7193 ("posix-cpu-timers: Cure
+SMP accounting oddities").
+
+Cure the problem by removing the cputimer->lock and rq->lock nesting,
+this leaves concurrent enablers doing duplicate work, but the time
+wasted should be on the same order otherwise wasted spinning on the
+lock and the greater-than assignment filter should ensure we preserve
+monotonicity.
+
+Reported-by: Dave Jones <davej@redhat.com>
+Reported-by: Simon Kirby <sim@hostway.ca>
+Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
+Cc: stable@kernel.org
+Cc: Linus Torvalds <torvalds@linux-foundation.org>
+Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
+Link: http://lkml.kernel.org/r/1318928713.21167.4.camel@twins
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+---
+ kernel/posix-cpu-timers.c |    7 ++++---
+ 1 files changed, 4 insertions(+), 3 deletions(-)
+
+diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
+index c8008dd..640ded8 100644
+--- a/kernel/posix-cpu-timers.c
++++ b/kernel/posix-cpu-timers.c
+@@ -274,9 +274,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
+ 	struct task_cputime sum;
+ 	unsigned long flags;
+ 
+-	spin_lock_irqsave(&cputimer->lock, flags);
+ 	if (!cputimer->running) {
+-		cputimer->running = 1;
+ 		/*
+ 		 * The POSIX timer interface allows for absolute time expiry
+ 		 * values through the TIMER_ABSTIME flag, therefore we have
+@@ -284,8 +282,11 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
+ 		 * it.
+ 		 */
+ 		thread_group_cputime(tsk, &sum);
++		spin_lock_irqsave(&cputimer->lock, flags);
++		cputimer->running = 1;
+ 		update_gt_cputime(&cputimer->cputime, &sum);
+-	}
++	} else
++		spin_lock_irqsave(&cputimer->lock, flags);
+ 	*times = cputimer->cputime;
+ 	spin_unlock_irqrestore(&cputimer->lock, flags);
+ }
+-- 
+1.7.7
+

debian/patches/features/all/rt/patch-3.0.6-rt18.patch

@@ -1,5 +1,7 @@
 [bwh: Dropped fix to kernel/taskstats.c applied separately in
  bugfix/all/Make-TASKSTATS-require-root-access.patch]
+[bwh: Updated raw spinlock changes in kernel/posix-cput-timers.c to apply after
+ bugfix/all/cputime-Cure-lock-inversion.patch]
 
 Index: linux-2.6/mm/memory.c
 ===================================================================
@@ -5964,18 +5966,17 @@ Index: linux-2.6/kernel/posix-cpu-timers.c
 ===================================================================
 --- linux-2.6.orig/kernel/posix-cpu-timers.c
 +++ linux-2.6/kernel/posix-cpu-timers.c
-@@ -274,7 +274,7 @@ void thread_group_cputimer(struct task_s
- 	struct task_cputime sum;
- 	unsigned long flags;
- 
--	spin_lock_irqsave(&cputimer->lock, flags);
-+	raw_spin_lock_irqsave(&cputimer->lock, flags);
- 	if (!cputimer->running) {
+@@ -280,13 +280,13 @@ void thread_group_cputimer(struct task_s
+ 		 * it.
+ 		 */
+ 		thread_group_cputime(tsk, &sum);
+-		spin_lock_irqsave(&cputimer->lock, flags);
++		raw_spin_lock_irqsave(&cputimer->lock, flags);
  		cputimer->running = 1;
- 		/*
-@@ -287,7 +287,7 @@ void thread_group_cputimer(struct task_s
  		update_gt_cputime(&cputimer->cputime, &sum);
- 	}
+ 	} else
+-		spin_lock_irqsave(&cputimer->lock, flags);
++		raw_spin_lock_irqsave(&cputimer->lock, flags);
  	*times = cputimer->cputime;
 -	spin_unlock_irqrestore(&cputimer->lock, flags);
 +	raw_spin_unlock_irqrestore(&cputimer->lock, flags);

debian/patches/series/6

@@ -1 +1,2 @@
 + bugfix/all/stable/3.0.7.patch
++ bugfix/all/cputimer-Cure-lock-inversion.patch