Commit 7e49fcce authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
Browse files

trace, lockdep: manual preempt count adding for local_bh_disable 



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: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent b06a8301

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

kernel/sched.c

+4 −4
Original line number Diff line number Diff line
@@ -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

kernel/softirq.c

+12 −1
Original line number Diff line number Diff line
@@ -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)

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