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Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm…
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…/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
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@torvalds
torvalds committed May 20, 2011
2 parents cbdad8d + 5db1256 commit 6595b4a
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Showing 4 changed files with 213 additions and 14 deletions.
4 changes: 2 additions & 2 deletions include/linux/seqlock.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
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2 changes: 1 addition & 1 deletion kernel/hung_task.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

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206 changes: 195 additions & 11 deletions kernel/lockdep.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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];
Expand Down Expand Up @@ -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:
Expand Down Expand Up @@ -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)
Expand All @@ -1109,13 +1172,17 @@ 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);
parent = get_lock_parent(parent);
}

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");
Expand Down Expand Up @@ -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;
}

Expand All @@ -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,
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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)
Expand All @@ -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");
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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");
Expand Down Expand Up @@ -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;

Expand All @@ -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");
Expand Down
15 changes: 15 additions & 0 deletions lib/Kconfig.debug
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down

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