From 7f6575f1fb963d5231afbceecd3feadb6ab58cd3 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Sat, 23 Feb 2013 17:28:45 +0100 Subject: 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] [] debug_smp_processor_id+0xdb/0xf0 [ 4.501716] [] native_sched_clock+0x22/0x80 [ 4.504434] [] sched_clock+0x9/0x10 [ 4.507185] [] fetch_task_cputime+0xad/0x120 [ 4.509916] [] task_cputime+0x35/0x60 [ 4.512622] [] acct_update_integrals+0x1e/0x40 [ 4.515372] [] do_execve_common+0x4ff/0x5c0 [ 4.518117] [] ? do_execve_common+0x144/0x5c0 [ 4.520844] [] ? rest_init+0x160/0x160 [ 4.523554] [] do_execve+0x37/0x40 [ 4.526276] [] run_init_process+0x23/0x30 [ 4.528953] [] kernel_init+0x9c/0xf0 [ 4.531608] [] 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 Reported-by: Ingo Molnar Suggested-by: Thomas Gleixner Signed-off-by: Frederic Weisbecker Cc: Li Zhong Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Kevin Hilman Link: http://lkml.kernel.org/r/1361636925-22288-3-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- 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 9857329ed280..ed12cbb135f4 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; -- cgit v1.2.3