[kernel/f16] Fix lock inversion causing hangs in 3.1-rc9 (rhbz #746485)

[Chuck Ebbert]

commit f73c1196beec64a5513d437be11d82540c859046
Author: Chuck Ebbert <cebbert at redhat.com>
Date:   Tue Oct 18 17:09:23 2011 -0400

    Fix lock inversion causing hangs in 3.1-rc9 (rhbz #746485)

 cputimer-cure-lock-inversion.patch |   73 ++++++++++++++++++++++++++++++++++++
 kernel.spec                        |    9 ++++
 2 files changed, 82 insertions(+), 0 deletions(-)
---
diff --git a/cputimer-cure-lock-inversion.patch b/cputimer-cure-lock-inversion.patch
new file mode 100644
index 0000000..cebb775
--- /dev/null
+++ b/cputimer-cure-lock-inversion.patch
@@ -0,0 +1,73 @@
+Subject: cputimer: Cure lock inversion
+From: Peter Zijlstra <a.p.zijlstra at chello.nl>
+Date: Mon Oct 17 11:50:30 CEST 2011
+
+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 at redhat.com>
+Reported-by: Simon Kirby <sim at hostway.ca>
+Cc: stable at kernel.org
+Cc: Thomas Gleixner <tglx at linutronix.de>
+Signed-off-by: Peter Zijlstra <a.p.zijlstra at chello.nl>
+---
+ kernel/posix-cpu-timers.c |    7 ++++---
+ 1 file changed, 4 insertions(+), 3 deletions(-)
+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
+@@ -274,9 +274,7 @@ void thread_group_cputimer(struct task_s
+ 	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_s
+ 		 * 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);
+ }
+
diff --git a/kernel.spec b/kernel.spec
index 3a359bd..808e104 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -748,6 +748,9 @@ Patch21002: mmc-Always-check-for-lower-base-frequency-quirk-for-.patch
 Patch21020: 0001-mm-vmscan-Limit-direct-reclaim-for-higher-order-allo.patch
 Patch21021: 0002-mm-Abort-reclaim-compaction-if-compaction-can-procee.patch
 
+# rhbz #746485
+Patch21030: cputimer-cure-lock-inversion.patch
+
 %endif
 
 BuildRoot: %{_tmppath}/kernel-%{KVERREL}-root
@@ -1377,6 +1380,9 @@ ApplyPatch utrace.patch
 ApplyPatch 0001-mm-vmscan-Limit-direct-reclaim-for-higher-order-allo.patch
 ApplyPatch 0002-mm-Abort-reclaim-compaction-if-compaction-can-procee.patch
 
+# rhbz #746485
+ApplyPatch cputimer-cure-lock-inversion.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -2078,6 +2084,9 @@ fi
 # and build.
 
 %changelog
+* Tue Oct 18 2011 Chuck Ebbert <cebbert at redhat.com>
+- Fix lock inversion causing hangs in 3.1-rc9 (rhbz #746485)
+
 * Tue Oct 18 2011 Josh Boyer <jwboyer at redhat.com>
 - Add patch to fix invalid EFI remap calls from Matt Fleming