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ftrace: printk and trace irqsoff and wakeups

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printk called from wakeup critical timings and irqs off can
cause deadlocks since printk might do a wakeup itself. If the
call to printk happens with the runqueue lock held, it can
deadlock.

This patch protects the printk from being called in trace irqs off
with a test to see if the runqueue for the current CPU is locked.
If it is locked, the printk is skipped.

The wakeup always holds the runqueue lock, so the printk is
simply removed.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Steven Rostedt 2008-05-12 21:20:54 +02:00 committed by Thomas Gleixner
parent 8f96da02c1
commit 4fe8c3048c
2 changed files with 14 additions and 25 deletions
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26
kernel/trace/trace_irqsoff.c
View file

@ -165,18 +165,20 @@ check_critical_timing(struct trace_array *tr,
update_max_tr_single(tr, current, cpu); update_max_tr_single(tr, current, cpu);
if (tracing_thresh) { if (!runqueue_is_locked()) {
printk(KERN_INFO "(%16s-%-5d|#%d):" if (tracing_thresh) {
" %lu us critical section violates %lu us threshold.\n", printk(KERN_INFO "(%16s-%-5d|#%d): %lu us critical"
current->comm, current->pid, " section violates %lu us threshold.\n",
raw_smp_processor_id(), current->comm, current->pid,
latency, nsecs_to_usecs(tracing_thresh)); raw_smp_processor_id(),
} else { latency, nsecs_to_usecs(tracing_thresh));
printk(KERN_INFO "(%16s-%-5d|#%d):" } else {
" new %lu us maximum-latency critical section.\n", printk(KERN_INFO "(%16s-%-5d|#%d): new %lu us"
current->comm, current->pid, " maximum-latency critical section.\n",
raw_smp_processor_id(), current->comm, current->pid,
latency); raw_smp_processor_id(),
latency);
}
} }
max_sequence++; max_sequence++;

13
kernel/trace/trace_sched_wakeup.c
View file

@ -106,19 +106,6 @@ wakeup_sched_switch(struct task_struct *prev, struct task_struct *next)
update_max_tr(tr, wakeup_task, wakeup_cpu); update_max_tr(tr, wakeup_task, wakeup_cpu);
if (tracing_thresh) {
printk(KERN_INFO "(%16s-%-5d|#%d):"
" %lu us wakeup latency violates %lu us threshold.\n",
wakeup_task->comm, wakeup_task->pid,
raw_smp_processor_id(),
latency, nsecs_to_usecs(tracing_thresh));
} else {
printk(KERN_INFO "(%16s-%-5d|#%d):"
" new %lu us maximum wakeup latency.\n",
wakeup_task->comm, wakeup_task->pid,
cpu, latency);
}
out_unlock: out_unlock:
__wakeup_reset(tr); __wakeup_reset(tr);
spin_unlock_irqrestore(&wakeup_lock, flags); spin_unlock_irqrestore(&wakeup_lock, flags);