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Commit 6595b4a9 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'core-locking-for-linus' of... 

Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  seqlock: Don't smp_rmb in seqlock reader spin loop
  watchdog, hung_task_timeout: Add Kconfig configurable default
  lockdep: Remove cmpxchg to update nr_chain_hlocks
  lockdep: Print a nicer description for simple irq lock inversions
  lockdep: Replace "Bad BFS generated tree" message with something less cryptic
  lockdep: Print a nicer description for irq inversion bugs
  lockdep: Print a nicer description for simple deadlocks
  lockdep: Print a nicer description for normal deadlocks
  lockdep: Print a nicer description for irq lock inversions
parents cbdad8dc 5db1256a

include/linux/seqlock.h

+2 −2
Original line number Diff line number Diff line
@@ -88,12 +88,12 @@ static __always_inline unsigned read_seqbegin(const seqlock_t *sl) 
	unsigned ret;



repeat:

	ret = sl->sequence;

	smp_rmb();

	ret = ACCESS_ONCE(sl->sequence);

	if (unlikely(ret & 1)) {

		cpu_relax();

		goto repeat;

	}

	smp_rmb();



	return ret;

}

kernel/hung_task.c

+1 −1
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT; 
/*

 * Zero means infinite timeout - no checking done:

 */

unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;

unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;



unsigned long __read_mostly sysctl_hung_task_warnings = 10;

kernel/lockdep.c

+195 −11
Original line number Diff line number Diff line
@@ -490,6 +490,18 @@ void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS]) 
	usage[i] = '\0';

}



static int __print_lock_name(struct lock_class *class)

{

	char str[KSYM_NAME_LEN];

	const char *name;



	name = class->name;

	if (!name)

		name = __get_key_name(class->key, str);



	return printk("%s", name);

}



static void print_lock_name(struct lock_class *class)

{

	char str[KSYM_NAME_LEN], usage[LOCK_USAGE_CHARS];
@@ -1053,6 +1065,56 @@ print_circular_bug_entry(struct lock_list *target, int depth) 
	return 0;

}



static void

print_circular_lock_scenario(struct held_lock *src,

			     struct held_lock *tgt,

			     struct lock_list *prt)

{

	struct lock_class *source = hlock_class(src);

	struct lock_class *target = hlock_class(tgt);

	struct lock_class *parent = prt->class;



	/*

	 * A direct locking problem where unsafe_class lock is taken

	 * directly by safe_class lock, then all we need to show

	 * is the deadlock scenario, as it is obvious that the

	 * unsafe lock is taken under the safe lock.

	 *

	 * But if there is a chain instead, where the safe lock takes

	 * an intermediate lock (middle_class) where this lock is

	 * not the same as the safe lock, then the lock chain is

	 * used to describe the problem. Otherwise we would need

	 * to show a different CPU case for each link in the chain

	 * from the safe_class lock to the unsafe_class lock.

	 */

	if (parent != source) {

		printk("Chain exists of:\n  ");

		__print_lock_name(source);

		printk(" --> ");

		__print_lock_name(parent);

		printk(" --> ");

		__print_lock_name(target);

		printk("\n\n");

	}



	printk(" Possible unsafe locking scenario:\n\n");

	printk("       CPU0                    CPU1\n");

	printk("       ----                    ----\n");

	printk("  lock(");

	__print_lock_name(target);

	printk(");\n");

	printk("                               lock(");

	__print_lock_name(parent);

	printk(");\n");

	printk("                               lock(");

	__print_lock_name(target);

	printk(");\n");

	printk("  lock(");

	__print_lock_name(source);

	printk(");\n");

	printk("\n *** DEADLOCK ***\n\n");

}



/*

 * When a circular dependency is detected, print the

 * header first:
@@ -1096,6 +1158,7 @@ static noinline int print_circular_bug(struct lock_list *this, 
{

	struct task_struct *curr = current;

	struct lock_list *parent;

	struct lock_list *first_parent;

	int depth;



	if (!debug_locks_off_graph_unlock() || debug_locks_silent)
@@ -1109,6 +1172,7 @@ static noinline int print_circular_bug(struct lock_list *this, 
	print_circular_bug_header(target, depth, check_src, check_tgt);



	parent = get_lock_parent(target);

	first_parent = parent;



	while (parent) {

		print_circular_bug_entry(parent, --depth);
@@ -1116,6 +1180,9 @@ static noinline int print_circular_bug(struct lock_list *this, 
	}



	printk("\nother info that might help us debug this:\n\n");

	print_circular_lock_scenario(check_src, check_tgt,

				     first_parent);



	lockdep_print_held_locks(curr);



	printk("\nstack backtrace:\n");
@@ -1314,7 +1381,7 @@ print_shortest_lock_dependencies(struct lock_list *leaf, 
		printk("\n");



		if (depth == 0 && (entry != root)) {

			printk("lockdep:%s bad BFS generated tree\n", __func__);

			printk("lockdep:%s bad path found in chain graph\n", __func__);

			break;

		}
@@ -1325,6 +1392,62 @@ print_shortest_lock_dependencies(struct lock_list *leaf, 
	return;

}



static void

print_irq_lock_scenario(struct lock_list *safe_entry,

			struct lock_list *unsafe_entry,

			struct lock_class *prev_class,

			struct lock_class *next_class)

{

	struct lock_class *safe_class = safe_entry->class;

	struct lock_class *unsafe_class = unsafe_entry->class;

	struct lock_class *middle_class = prev_class;



	if (middle_class == safe_class)

		middle_class = next_class;



	/*

	 * A direct locking problem where unsafe_class lock is taken

	 * directly by safe_class lock, then all we need to show

	 * is the deadlock scenario, as it is obvious that the

	 * unsafe lock is taken under the safe lock.

	 *

	 * But if there is a chain instead, where the safe lock takes

	 * an intermediate lock (middle_class) where this lock is

	 * not the same as the safe lock, then the lock chain is

	 * used to describe the problem. Otherwise we would need

	 * to show a different CPU case for each link in the chain

	 * from the safe_class lock to the unsafe_class lock.

	 */

	if (middle_class != unsafe_class) {

		printk("Chain exists of:\n  ");

		__print_lock_name(safe_class);

		printk(" --> ");

		__print_lock_name(middle_class);

		printk(" --> ");

		__print_lock_name(unsafe_class);

		printk("\n\n");

	}



	printk(" Possible interrupt unsafe locking scenario:\n\n");

	printk("       CPU0                    CPU1\n");

	printk("       ----                    ----\n");

	printk("  lock(");

	__print_lock_name(unsafe_class);

	printk(");\n");

	printk("                               local_irq_disable();\n");

	printk("                               lock(");

	__print_lock_name(safe_class);

	printk(");\n");

	printk("                               lock(");

	__print_lock_name(middle_class);

	printk(");\n");

	printk("  <Interrupt>\n");

	printk("    lock(");

	__print_lock_name(safe_class);

	printk(");\n");

	printk("\n *** DEADLOCK ***\n\n");

}



static int

print_bad_irq_dependency(struct task_struct *curr,

			 struct lock_list *prev_root,
@@ -1376,6 +1499,9 @@ print_bad_irq_dependency(struct task_struct *curr, 
	print_stack_trace(forwards_entry->class->usage_traces + bit2, 1);



	printk("\nother info that might help us debug this:\n\n");

	print_irq_lock_scenario(backwards_entry, forwards_entry,

				hlock_class(prev), hlock_class(next));



	lockdep_print_held_locks(curr);



	printk("\nthe dependencies between %s-irq-safe lock", irqclass);
@@ -1539,6 +1665,26 @@ static inline void inc_chains(void) 


#endif



static void

print_deadlock_scenario(struct held_lock *nxt,

			     struct held_lock *prv)

{

	struct lock_class *next = hlock_class(nxt);

	struct lock_class *prev = hlock_class(prv);



	printk(" Possible unsafe locking scenario:\n\n");

	printk("       CPU0\n");

	printk("       ----\n");

	printk("  lock(");

	__print_lock_name(prev);

	printk(");\n");

	printk("  lock(");

	__print_lock_name(next);

	printk(");\n");

	printk("\n *** DEADLOCK ***\n\n");

	printk(" May be due to missing lock nesting notation\n\n");

}



static int

print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,

		   struct held_lock *next)
@@ -1557,6 +1703,7 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev, 
	print_lock(prev);



	printk("\nother info that might help us debug this:\n");

	print_deadlock_scenario(next, prev);

	lockdep_print_held_locks(curr);



	printk("\nstack backtrace:\n");
@@ -1826,7 +1973,7 @@ static inline int lookup_chain_cache(struct task_struct *curr, 
	struct list_head *hash_head = chainhashentry(chain_key);

	struct lock_chain *chain;

	struct held_lock *hlock_curr, *hlock_next;

	int i, j, n, cn;

	int i, j;



	if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))

		return 0;
@@ -1886,15 +2033,9 @@ static inline int lookup_chain_cache(struct task_struct *curr, 
	}

	i++;

	chain->depth = curr->lockdep_depth + 1 - i;

	cn = nr_chain_hlocks;

	while (cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS) {

		n = cmpxchg(&nr_chain_hlocks, cn, cn + chain->depth);

		if (n == cn)

			break;

		cn = n;

	}

	if (likely(cn + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {

		chain->base = cn;

	if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) {

		chain->base = nr_chain_hlocks;

		nr_chain_hlocks += chain->depth;

		for (j = 0; j < chain->depth - 1; j++, i++) {

			int lock_id = curr->held_locks[i].class_idx - 1;

			chain_hlocks[chain->base + j] = lock_id;
@@ -2011,6 +2152,24 @@ static void check_chain_key(struct task_struct *curr) 
#endif

}



static void

print_usage_bug_scenario(struct held_lock *lock)

{

	struct lock_class *class = hlock_class(lock);



	printk(" Possible unsafe locking scenario:\n\n");

	printk("       CPU0\n");

	printk("       ----\n");

	printk("  lock(");

	__print_lock_name(class);

	printk(");\n");

	printk("  <Interrupt>\n");

	printk("    lock(");

	__print_lock_name(class);

	printk(");\n");

	printk("\n *** DEADLOCK ***\n\n");

}



static int

print_usage_bug(struct task_struct *curr, struct held_lock *this,

		enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
@@ -2039,6 +2198,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this, 


	print_irqtrace_events(curr);

	printk("\nother info that might help us debug this:\n");

	print_usage_bug_scenario(this);



	lockdep_print_held_locks(curr);



	printk("\nstack backtrace:\n");
@@ -2073,6 +2234,10 @@ print_irq_inversion_bug(struct task_struct *curr, 
			struct held_lock *this, int forwards,

			const char *irqclass)

{

	struct lock_list *entry = other;

	struct lock_list *middle = NULL;

	int depth;



	if (!debug_locks_off_graph_unlock() || debug_locks_silent)

		return 0;
@@ -2091,6 +2256,25 @@ print_irq_inversion_bug(struct task_struct *curr, 
	printk("\n\nand interrupts could create inverse lock ordering between them.\n\n");



	printk("\nother info that might help us debug this:\n");



	/* Find a middle lock (if one exists) */

	depth = get_lock_depth(other);

	do {

		if (depth == 0 && (entry != root)) {

			printk("lockdep:%s bad path found in chain graph\n", __func__);

			break;

		}

		middle = entry;

		entry = get_lock_parent(entry);

		depth--;

	} while (entry && entry != root && (depth >= 0));

	if (forwards)

		print_irq_lock_scenario(root, other,

			middle ? middle->class : root->class, other->class);

	else

		print_irq_lock_scenario(other, root,

			middle ? middle->class : other->class, root->class);



	lockdep_print_held_locks(curr);



	printk("\nthe shortest dependencies between 2nd lock and 1st lock:\n");

lib/Kconfig.debug

+15 −0
Original line number Diff line number Diff line
@@ -238,6 +238,21 @@ config DETECT_HUNG_TASK 
	  enabled then all held locks will also be reported. This

	  feature has negligible overhead.



config DEFAULT_HUNG_TASK_TIMEOUT

	int "Default timeout for hung task detection (in seconds)"

	depends on DETECT_HUNG_TASK

	default 120

	help

	  This option controls the default timeout (in seconds) used

	  to determine when a task has become non-responsive and should

	  be considered hung.



	  It can be adjusted at runtime via the kernel.hung_task_timeout

	  sysctl or by writing a value to /proc/sys/kernel/hung_task_timeout.



	  A timeout of 0 disables the check.  The default is two minutes.

	  Keeping the default should be fine in most cases.



config BOOTPARAM_HUNG_TASK_PANIC

	bool "Panic (Reboot) On Hung Tasks"

	depends on DETECT_HUNG_TASK