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trace, lockdep: manual preempt count adding for local_bh_disable

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Impact: fix to preempt trace triggering lockdep check_flag failure

In local_bh_disable, the use of add_preempt_count causes the
preempt tracer to start recording the time preemption is off.
But because it already modified the preempt_count to show
softirqs disabled, and before it called the lockdep code to
handle this, it causes a state that lockdep can not handle.

The preempt tracer will reset the ring buffer on start of a trace,
and the ring buffer reset code does a spin_lock_irqsave. This
calls into lockdep and lockdep will fail when it detects the
invalid state of having softirqs disabled but the internal
current->softirqs_enabled is still set.

The fix is to manually add the SOFTIRQ_OFFSET to preempt count
and call the preempt tracer code outside the lockdep critical
area.

Thanks to Peter Zijlstra for suggesting this solution.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Rostedt 2009-01-22 19:01:40 -05:00 committed by Ingo Molnar
parent b06a830183
commit 7e49fcce1b
3 changed files with 18 additions and 5 deletions
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2
include/linux/sched.h
View file

@ -137,6 +137,8 @@ extern unsigned long nr_uninterruptible(void);
extern unsigned long nr_active(void);
extern unsigned long nr_iowait(void);
extern unsigned long get_parent_ip(unsigned long addr);
struct seq_file;
struct cfs_rq;
struct task_group;

8
kernel/sched.c
View file

@ -4399,10 +4399,7 @@ void scheduler_tick(void)
#endif
}
#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \
defined(CONFIG_PREEMPT_TRACER))
static inline unsigned long get_parent_ip(unsigned long addr)
unsigned long get_parent_ip(unsigned long addr)
{
if (in_lock_functions(addr)) {
addr = CALLER_ADDR2;
@ -4412,6 +4409,9 @@ static inline unsigned long get_parent_ip(unsigned long addr)
return addr;
}
#if defined(CONFIG_PREEMPT) && (defined(CONFIG_DEBUG_PREEMPT) || \
defined(CONFIG_PREEMPT_TRACER))
void __kprobes add_preempt_count(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT

13
kernel/softirq.c
View file

@ -21,6 +21,7 @@
#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/rcupdate.h>
#include <linux/ftrace.h>
#include <linux/smp.h>
#include <linux/tick.h>
@ -79,13 +80,23 @@ static void __local_bh_disable(unsigned long ip)
WARN_ON_ONCE(in_irq());
raw_local_irq_save(flags);
add_preempt_count(SOFTIRQ_OFFSET);
/*
* The preempt tracer hooks into add_preempt_count and will break
* lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
* is set and before current->softirq_enabled is cleared.
* We must manually increment preempt_count here and manually
* call the trace_preempt_off later.
*/
preempt_count() += SOFTIRQ_OFFSET;
/*
* Were softirqs turned off above:
*/
if (softirq_count() == SOFTIRQ_OFFSET)
trace_softirqs_off(ip);
raw_local_irq_restore(flags);
if (preempt_count() == SOFTIRQ_OFFSET)
trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
}
#else /* !CONFIG_TRACE_IRQFLAGS */
static inline void __local_bh_disable(unsigned long ip)