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Commit d1c6d149 authored by Vegard Nossum's avatar Vegard Nossum Committed by Ingo Molnar
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sched/debug: Make the "Preemption disabled at ..." message more useful 

This message is currently really useless since it always prints a value
that comes from the printk() we just did, e.g.:

    BUG: sleeping function called from invalid context at mm/slab.h:388
    in_atomic(): 0, irqs_disabled(): 0, pid: 31996, name: trinity-c1
    Preemption disabled at:[<ffffffff8119db33>] down_trylock+0x13/0x80

    BUG: sleeping function called from invalid context at include/linux/freezer.h:56
    in_atomic(): 0, irqs_disabled(): 0, pid: 31996, name: trinity-c1
    Preemption disabled at:[<ffffffff811aaa37>] console_unlock+0x2f7/0x930

Here, both down_trylock() and console_unlock() is somewhere in the
printk() path.

We should save the value before calling printk() and use the saved value
instead. That immediately reveals the offending callsite:

    BUG: sleeping function called from invalid context at mm/slab.h:388
    in_atomic(): 0, irqs_disabled(): 0, pid: 14971, name: trinity-c2
    Preemption disabled at:[<ffffffff819bcd46>] rhashtable_walk_start+0x46/0x150

Bug report:

  http://marc.info/?l=linux-netdev&m=146925979821849&w=2



Signed-off-by: default avatarVegard Nossum <vegard.nossum@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russel <rusty@rustcorp.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 98b0a857

include/linux/sched.h

+9 −0
Original line number Diff line number Diff line
@@ -3236,6 +3236,15 @@ static inline void cond_resched_rcu(void) 
#endif

}



static inline unsigned long get_preempt_disable_ip(struct task_struct *p)

{

#ifdef CONFIG_DEBUG_PREEMPT

	return p->preempt_disable_ip;

#else

	return 0;

#endif

}



/*

 * Does a critical section need to be broken due to another

 * task waiting?: (technically does not depend on CONFIG_PREEMPT,

kernel/sched/core.c

+13 −8
Original line number Diff line number Diff line
@@ -3171,6 +3171,9 @@ static inline void preempt_latency_stop(int val) { } 
 */

static noinline void __schedule_bug(struct task_struct *prev)

{

	/* Save this before calling printk(), since that will clobber it */

	unsigned long preempt_disable_ip = get_preempt_disable_ip(current);



	if (oops_in_progress)

		return;
@@ -3181,13 +3184,12 @@ static noinline void __schedule_bug(struct task_struct *prev) 
	print_modules();

	if (irqs_disabled())

		print_irqtrace_events(prev);

#ifdef CONFIG_DEBUG_PREEMPT

	if (in_atomic_preempt_off()) {

	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)

	    && in_atomic_preempt_off()) {

		pr_err("Preemption disabled at:");

		print_ip_sym(current->preempt_disable_ip);

		print_ip_sym(preempt_disable_ip);

		pr_cont("\n");

	}

#endif

	if (panic_on_warn)

		panic("scheduling while atomic\n");
@@ -7571,6 +7573,7 @@ EXPORT_SYMBOL(__might_sleep); 
void ___might_sleep(const char *file, int line, int preempt_offset)

{

	static unsigned long prev_jiffy;	/* ratelimiting */

	unsigned long preempt_disable_ip;



	rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */

	if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
@@ -7581,6 +7584,9 @@ void ___might_sleep(const char *file, int line, int preempt_offset) 
		return;

	prev_jiffy = jiffies;



	/* Save this before calling printk(), since that will clobber it */

	preempt_disable_ip = get_preempt_disable_ip(current);



	printk(KERN_ERR

		"BUG: sleeping function called from invalid context at %s:%d\n",

			file, line);
@@ -7595,13 +7601,12 @@ void ___might_sleep(const char *file, int line, int preempt_offset) 
	debug_show_held_locks(current);

	if (irqs_disabled())

		print_irqtrace_events(current);

#ifdef CONFIG_DEBUG_PREEMPT

	if (!preempt_count_equals(preempt_offset)) {

	if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)

	    && !preempt_count_equals(preempt_offset)) {

		pr_err("Preemption disabled at:");

		print_ip_sym(current->preempt_disable_ip);

		print_ip_sym(preempt_disable_ip);

		pr_cont("\n");

	}

#endif

	dump_stack();

}

EXPORT_SYMBOL(___might_sleep);