linux-kernel - [tip:sched/urgent] cputime: Use local_clock() for full dynticks cputime accounting

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Message-ID: <tip-7f6575f1fb963d5231afbceecd3feadb6ab58cd3@git.kernel.org>
Date:	Sun, 24 Feb 2013 04:22:57 -0800
From:	tip-bot for Frederic Weisbecker <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	peterz@...radead.org, zhong@...ux.vnet.ibm.com, fweisbec@...il.com,
	rostedt@...dmis.org, tglx@...utronix.de, khilman@...aro.org
Subject: [tip:sched/urgent] cputime: Use local_clock()
  for full dynticks cputime accounting

Commit-ID:  7f6575f1fb963d5231afbceecd3feadb6ab58cd3
Gitweb:     http://git.kernel.org/tip/7f6575f1fb963d5231afbceecd3feadb6ab58cd3
Author:     Frederic Weisbecker <fweisbec@...il.com>
AuthorDate: Sat, 23 Feb 2013 17:28:45 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sun, 24 Feb 2013 12:57:16 +0100

cputime: Use local_clock() for full dynticks cputime accounting

Running the full dynticks cputime accounting with preemptible
kernel debugging trigger the following warning:

	[    4.488303] BUG: using smp_processor_id() in preemptible [00000000] code: init/1
	[    4.490971] caller is native_sched_clock+0x22/0x80
	[    4.493663] Pid: 1, comm: init Not tainted 3.8.0+ #13
	[    4.496376] Call Trace:
	[    4.498996]  [<ffffffff813410eb>] debug_smp_processor_id+0xdb/0xf0
	[    4.501716]  [<ffffffff8101e642>] native_sched_clock+0x22/0x80
	[    4.504434]  [<ffffffff8101db99>] sched_clock+0x9/0x10
	[    4.507185]  [<ffffffff81096ccd>] fetch_task_cputime+0xad/0x120
	[    4.509916]  [<ffffffff81096dd5>] task_cputime+0x35/0x60
	[    4.512622]  [<ffffffff810f146e>] acct_update_integrals+0x1e/0x40
	[    4.515372]  [<ffffffff8117d2cf>] do_execve_common+0x4ff/0x5c0
	[    4.518117]  [<ffffffff8117cf14>] ? do_execve_common+0x144/0x5c0
	[    4.520844]  [<ffffffff81867a10>] ? rest_init+0x160/0x160
	[    4.523554]  [<ffffffff8117d457>] do_execve+0x37/0x40
	[    4.526276]  [<ffffffff810021a3>] run_init_process+0x23/0x30
	[    4.528953]  [<ffffffff81867aac>] kernel_init+0x9c/0xf0
	[    4.531608]  [<ffffffff8188356c>] ret_from_fork+0x7c/0xb0

We use sched_clock() to perform and fixup the cputime
accounting. However we are calling it with preemption enabled
from the read side, which trigger the bug above.

To fix this up, use local_clock() instead. It takes care of
preemption and also provide a more reliable clock source. This
is welcome for this kind of statistic that is widely relied on
in userspace.

Reported-by: Thomas Gleixner <tglx@...utronix.de>
Reported-by: Ingo Molnar <mingo@...nel.org>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Kevin Hilman <khilman@...aro.org>
Link: http://lkml.kernel.org/r/1361636925-22288-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/cputime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 9857329..ed12cbb 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -604,7 +604,7 @@ static unsigned long long vtime_delta(struct task_struct *tsk)
 {
 	unsigned long long clock;
 
-	clock = sched_clock();
+	clock = local_clock();
 	if (clock < tsk->vtime_snap)
 		return 0;
 
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