Commit c7eba51c authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull locking updates from Ingo Molnar:

 - improve rwsem scalability

 - add uninitialized rwsem debugging check

 - reduce lockdep's stacktrace memory usage and add diagnostics

 - misc cleanups, code consolidation and constification

* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  mutex: Fix up mutex_waiter usage
  locking/mutex: Use mutex flags macro instead of hard code
  locking/mutex: Make __mutex_owner static to mutex.c
  locking/qspinlock,x86: Clarify virt_spin_lock_key
  locking/rwsem: Check for operations on an uninitialized rwsem
  locking/rwsem: Make handoff writer optimistically spin on owner
  locking/lockdep: Report more stack trace statistics
  locking/lockdep: Reduce space occupied by stack traces
  stacktrace: Constify 'entries' arguments
  locking/lockdep: Make it clear that what lock_class::key points at is not modified
parents cc9b499a e57d1430
......@@ -63,10 +63,25 @@ static inline bool vcpu_is_preempted(long cpu)
#endif
#ifdef CONFIG_PARAVIRT
/*
* virt_spin_lock_key - enables (by default) the virt_spin_lock() hijack.
*
* Native (and PV wanting native due to vCPU pinning) should disable this key.
* It is done in this backwards fashion to only have a single direction change,
* which removes ordering between native_pv_spin_init() and HV setup.
*/
DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
void native_pv_lock_init(void) __init;
/*
* Shortcut for the queued_spin_lock_slowpath() function that allows
* virt to hijack it.
*
* Returns:
* true - lock has been negotiated, all done;
* false - queued_spin_lock_slowpath() will do its thing.
*/
#define virt_spin_lock virt_spin_lock
static inline bool virt_spin_lock(struct qspinlock *lock)
{
......
......@@ -66,10 +66,7 @@ struct lock_class_key {
extern struct lock_class_key __lockdep_no_validate__;
struct lock_trace {
unsigned int nr_entries;
unsigned int offset;
};
struct lock_trace;
#define LOCKSTAT_POINTS 4
......@@ -97,7 +94,7 @@ struct lock_class {
*/
struct list_head locks_after, locks_before;
struct lockdep_subclass_key *key;
const struct lockdep_subclass_key *key;
unsigned int subclass;
unsigned int dep_gen_id;
......@@ -105,7 +102,7 @@ struct lock_class {
* IRQ/softirq usage tracking bits:
*/
unsigned long usage_mask;
struct lock_trace usage_traces[XXX_LOCK_USAGE_STATES];
const struct lock_trace *usage_traces[XXX_LOCK_USAGE_STATES];
/*
* Generation counter, when doing certain classes of graph walking,
......@@ -193,7 +190,7 @@ struct lock_list {
struct list_head entry;
struct lock_class *class;
struct lock_class *links_to;
struct lock_trace trace;
const struct lock_trace *trace;
int distance;
/*
......
......@@ -65,16 +65,6 @@ struct mutex {
#endif
};
/*
* Internal helper function; C doesn't allow us to hide it :/
*
* DO NOT USE (outside of mutex code).
*/
static inline struct task_struct *__mutex_owner(struct mutex *lock)
{
return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
}
/*
* This is the control structure for tasks blocked on mutex,
* which resides on the blocked task's kernel stack:
......@@ -144,10 +134,7 @@ extern void __mutex_init(struct mutex *lock, const char *name,
*
* Returns true if the mutex is locked, false if unlocked.
*/
static inline bool mutex_is_locked(struct mutex *lock)
{
return __mutex_owner(lock) != NULL;
}
extern bool mutex_is_locked(struct mutex *lock);
/*
* See kernel/locking/mutex.c for detailed documentation of these APIs.
......@@ -220,13 +207,7 @@ enum mutex_trylock_recursive_enum {
* - MUTEX_TRYLOCK_SUCCESS - lock acquired,
* - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
*/
static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
mutex_trylock_recursive(struct mutex *lock)
{
if (unlikely(__mutex_owner(lock) == current))
return MUTEX_TRYLOCK_RECURSIVE;
return mutex_trylock(lock);
}
extern /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
mutex_trylock_recursive(struct mutex *lock);
#endif /* __LINUX_MUTEX_H */
......@@ -45,6 +45,9 @@ struct rw_semaphore {
#endif
raw_spinlock_t wait_lock;
struct list_head wait_list;
#ifdef CONFIG_DEBUG_RWSEMS
void *magic;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
......@@ -73,6 +76,12 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif
#ifdef CONFIG_DEBUG_RWSEMS
# define __DEBUG_RWSEM_INITIALIZER(lockname) , .magic = &lockname
#else
# define __DEBUG_RWSEM_INITIALIZER(lockname)
#endif
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED
#else
......@@ -85,6 +94,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
.wait_list = LIST_HEAD_INIT((name).wait_list), \
.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
__RWSEM_OPT_INIT(name) \
__DEBUG_RWSEM_INITIALIZER(name) \
__RWSEM_DEP_MAP_INIT(name) }
#define DECLARE_RWSEM(name) \
......
......@@ -9,9 +9,9 @@ struct task_struct;
struct pt_regs;
#ifdef CONFIG_STACKTRACE
void stack_trace_print(unsigned long *trace, unsigned int nr_entries,
void stack_trace_print(const unsigned long *trace, unsigned int nr_entries,
int spaces);
int stack_trace_snprint(char *buf, size_t size, unsigned long *entries,
int stack_trace_snprint(char *buf, size_t size, const unsigned long *entries,
unsigned int nr_entries, int spaces);
unsigned int stack_trace_save(unsigned long *store, unsigned int size,
unsigned int skipnr);
......
......@@ -449,33 +449,101 @@ static void print_lockdep_off(const char *bug_msg)
unsigned long nr_stack_trace_entries;
#ifdef CONFIG_PROVE_LOCKING
/**
* struct lock_trace - single stack backtrace
* @hash_entry: Entry in a stack_trace_hash[] list.
* @hash: jhash() of @entries.
* @nr_entries: Number of entries in @entries.
* @entries: Actual stack backtrace.
*/
struct lock_trace {
struct hlist_node hash_entry;
u32 hash;
u32 nr_entries;
unsigned long entries[0] __aligned(sizeof(unsigned long));
};
#define LOCK_TRACE_SIZE_IN_LONGS \
(sizeof(struct lock_trace) / sizeof(unsigned long))
/*
* Stack-trace: tightly packed array of stack backtrace
* addresses. Protected by the graph_lock.
* Stack-trace: sequence of lock_trace structures. Protected by the graph_lock.
*/
static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];
static struct hlist_head stack_trace_hash[STACK_TRACE_HASH_SIZE];
static bool traces_identical(struct lock_trace *t1, struct lock_trace *t2)
{
return t1->hash == t2->hash && t1->nr_entries == t2->nr_entries &&
memcmp(t1->entries, t2->entries,
t1->nr_entries * sizeof(t1->entries[0])) == 0;
}
static int save_trace(struct lock_trace *trace)
static struct lock_trace *save_trace(void)
{
unsigned long *entries = stack_trace + nr_stack_trace_entries;
struct lock_trace *trace, *t2;
struct hlist_head *hash_head;
u32 hash;
unsigned int max_entries;
trace->offset = nr_stack_trace_entries;
max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
trace->nr_entries = stack_trace_save(entries, max_entries, 3);
nr_stack_trace_entries += trace->nr_entries;
BUILD_BUG_ON_NOT_POWER_OF_2(STACK_TRACE_HASH_SIZE);
BUILD_BUG_ON(LOCK_TRACE_SIZE_IN_LONGS >= MAX_STACK_TRACE_ENTRIES);
trace = (struct lock_trace *)(stack_trace + nr_stack_trace_entries);
max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries -
LOCK_TRACE_SIZE_IN_LONGS;
trace->nr_entries = stack_trace_save(trace->entries, max_entries, 3);
if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES -
LOCK_TRACE_SIZE_IN_LONGS - 1) {
if (!debug_locks_off_graph_unlock())
return 0;
return NULL;
print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
dump_stack();
return 0;
return NULL;
}
return 1;
hash = jhash(trace->entries, trace->nr_entries *
sizeof(trace->entries[0]), 0);
trace->hash = hash;
hash_head = stack_trace_hash + (hash & (STACK_TRACE_HASH_SIZE - 1));
hlist_for_each_entry(t2, hash_head, hash_entry) {
if (traces_identical(trace, t2))
return t2;
}
nr_stack_trace_entries += LOCK_TRACE_SIZE_IN_LONGS + trace->nr_entries;
hlist_add_head(&trace->hash_entry, hash_head);
return trace;
}
/* Return the number of stack traces in the stack_trace[] array. */
u64 lockdep_stack_trace_count(void)
{
struct lock_trace *trace;
u64 c = 0;
int i;
for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++) {
hlist_for_each_entry(trace, &stack_trace_hash[i], hash_entry) {
c++;
}
}
return c;
}
/* Return the number of stack hash chains that have at least one stack trace. */
u64 lockdep_stack_hash_count(void)
{
u64 c = 0;
int i;
for (i = 0; i < ARRAY_SIZE(stack_trace_hash); i++)
if (!hlist_empty(&stack_trace_hash[i]))
c++;
return c;
}
#endif
......@@ -511,7 +579,7 @@ static const char *usage_str[] =
};
#endif
const char * __get_key_name(struct lockdep_subclass_key *key, char *str)
const char *__get_key_name(const struct lockdep_subclass_key *key, char *str)
{
return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
}
......@@ -1235,7 +1303,7 @@ static struct lock_list *alloc_list_entry(void)
static int add_lock_to_list(struct lock_class *this,
struct lock_class *links_to, struct list_head *head,
unsigned long ip, int distance,
struct lock_trace *trace)
const struct lock_trace *trace)
{
struct lock_list *entry;
/*
......@@ -1249,7 +1317,7 @@ static int add_lock_to_list(struct lock_class *this,
entry->class = this;
entry->links_to = links_to;
entry->distance = distance;
entry->trace = *trace;
entry->trace = trace;
/*
* Both allocation and removal are done under the graph lock; but
* iteration is under RCU-sched; see look_up_lock_class() and
......@@ -1470,11 +1538,10 @@ static inline int __bfs_backwards(struct lock_list *src_entry,
}
static void print_lock_trace(struct lock_trace *trace, unsigned int spaces)
static void print_lock_trace(const struct lock_trace *trace,
unsigned int spaces)
{
unsigned long *entries = stack_trace + trace->offset;
stack_trace_print(entries, trace->nr_entries, spaces);
stack_trace_print(trace->entries, trace->nr_entries, spaces);
}
/*
......@@ -1489,7 +1556,7 @@ print_circular_bug_entry(struct lock_list *target, int depth)
printk("\n-> #%u", depth);
print_lock_name(target->class);
printk(KERN_CONT ":\n");
print_lock_trace(&target->trace, 6);
print_lock_trace(target->trace, 6);
}
static void
......@@ -1592,7 +1659,8 @@ static noinline void print_circular_bug(struct lock_list *this,
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
return;
if (!save_trace(&this->trace))
this->trace = save_trace();
if (!this->trace)
return;
depth = get_lock_depth(target);
......@@ -1715,7 +1783,7 @@ check_path(struct lock_class *target, struct lock_list *src_entry,
*/
static noinline int
check_noncircular(struct held_lock *src, struct held_lock *target,
struct lock_trace *trace)
struct lock_trace **const trace)
{
int ret;
struct lock_list *uninitialized_var(target_entry);
......@@ -1729,13 +1797,13 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
ret = check_path(hlock_class(target), &src_entry, &target_entry);
if (unlikely(!ret)) {
if (!trace->nr_entries) {
if (!*trace) {
/*
* If save_trace fails here, the printing might
* trigger a WARN but because of the !nr_entries it
* should not do bad things.
*/
save_trace(trace);
*trace = save_trace();
}
print_circular_bug(&src_entry, target_entry, src, target);
......@@ -1859,7 +1927,7 @@ static void print_lock_class_header(struct lock_class *class, int depth)
len += printk("%*s %s", depth, "", usage_str[bit]);
len += printk(KERN_CONT " at:\n");
print_lock_trace(class->usage_traces + bit, len);
print_lock_trace(class->usage_traces[bit], len);
}
}
printk("%*s }\n", depth, "");
......@@ -1884,7 +1952,7 @@ print_shortest_lock_dependencies(struct lock_list *leaf,
do {
print_lock_class_header(entry->class, depth);
printk("%*s ... acquired at:\n", depth, "");
print_lock_trace(&entry->trace, 2);
print_lock_trace(entry->trace, 2);
printk("\n");
if (depth == 0 && (entry != root)) {
......@@ -1995,14 +2063,14 @@ print_bad_irq_dependency(struct task_struct *curr,
print_lock_name(backwards_entry->class);
pr_warn("\n... which became %s-irq-safe at:\n", irqclass);
print_lock_trace(backwards_entry->class->usage_traces + bit1, 1);
print_lock_trace(backwards_entry->class->usage_traces[bit1], 1);
pr_warn("\nto a %s-irq-unsafe lock:\n", irqclass);
print_lock_name(forwards_entry->class);
pr_warn("\n... which became %s-irq-unsafe at:\n", irqclass);
pr_warn("...");
print_lock_trace(forwards_entry->class->usage_traces + bit2, 1);
print_lock_trace(forwards_entry->class->usage_traces[bit2], 1);
pr_warn("\nother info that might help us debug this:\n\n");
print_irq_lock_scenario(backwards_entry, forwards_entry,
......@@ -2011,13 +2079,15 @@ print_bad_irq_dependency(struct task_struct *curr,
lockdep_print_held_locks(curr);
pr_warn("\nthe dependencies between %s-irq-safe lock and the holding lock:\n", irqclass);
if (!save_trace(&prev_root->trace))
prev_root->trace = save_trace();
if (!prev_root->trace)
return;
print_shortest_lock_dependencies(backwards_entry, prev_root);
pr_warn("\nthe dependencies between the lock to be acquired");
pr_warn(" and %s-irq-unsafe lock:\n", irqclass);
if (!save_trace(&next_root->trace))
next_root->trace = save_trace();
if (!next_root->trace)
return;
print_shortest_lock_dependencies(forwards_entry, next_root);
......@@ -2369,7 +2439,8 @@ check_deadlock(struct task_struct *curr, struct held_lock *next)
*/
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
struct held_lock *next, int distance, struct lock_trace *trace)
struct held_lock *next, int distance,
struct lock_trace **const trace)
{
struct lock_list *entry;
int ret;
......@@ -2444,8 +2515,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
return ret;
#endif
if (!trace->nr_entries && !save_trace(trace))
return 0;
if (!*trace) {
*trace = save_trace();
if (!*trace)
return 0;
}
/*
* Ok, all validations passed, add the new lock
......@@ -2453,14 +2527,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
&hlock_class(prev)->locks_after,
next->acquire_ip, distance, trace);
next->acquire_ip, distance, *trace);
if (!ret)
return 0;
ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
&hlock_class(next)->locks_before,
next->acquire_ip, distance, trace);
next->acquire_ip, distance, *trace);
if (!ret)
return 0;
......@@ -2476,7 +2550,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
static int
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
struct lock_trace trace = { .nr_entries = 0 };
struct lock_trace *trace = NULL;
int depth = curr->lockdep_depth;
struct held_lock *hlock;
......@@ -3015,7 +3089,7 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
print_lock(this);
pr_warn("{%s} state was registered at:\n", usage_str[prev_bit]);
print_lock_trace(hlock_class(this)->usage_traces + prev_bit, 1);
print_lock_trace(hlock_class(this)->usage_traces[prev_bit], 1);
print_irqtrace_events(curr);
pr_warn("\nother info that might help us debug this:\n");
......@@ -3096,7 +3170,8 @@ print_irq_inversion_bug(struct task_struct *curr,
lockdep_print_held_locks(curr);
pr_warn("\nthe shortest dependencies between 2nd lock and 1st lock:\n");
if (!save_trace(&root->trace))
root->trace = save_trace();
if (!root->trace)
return;
print_shortest_lock_dependencies(other, root);
......@@ -3580,7 +3655,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
hlock_class(this)->usage_mask |= new_mask;
if (!save_trace(hlock_class(this)->usage_traces + new_bit))
if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))
return 0;
switch (new_bit) {
......@@ -5157,6 +5232,12 @@ void __init lockdep_init(void)
) / 1024
);
#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
printk(" memory used for stack traces: %zu kB\n",
(sizeof(stack_trace) + sizeof(stack_trace_hash)) / 1024
);
#endif
printk(" per task-struct memory footprint: %zu bytes\n",
sizeof(((struct task_struct *)NULL)->held_locks));
}
......
......@@ -92,6 +92,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
#define MAX_LOCKDEP_ENTRIES 16384UL
#define MAX_LOCKDEP_CHAINS_BITS 15
#define MAX_STACK_TRACE_ENTRIES 262144UL
#define STACK_TRACE_HASH_SIZE 8192
#else
#define MAX_LOCKDEP_ENTRIES 32768UL
......@@ -102,6 +103,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
* addresses. Protected by the hash_lock.
*/
#define MAX_STACK_TRACE_ENTRIES 524288UL
#define STACK_TRACE_HASH_SIZE 16384
#endif
#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)
......@@ -116,7 +118,8 @@ extern struct lock_chain lock_chains[];
extern void get_usage_chars(struct lock_class *class,
char usage[LOCK_USAGE_CHARS]);
extern const char * __get_key_name(struct lockdep_subclass_key *key, char *str);
extern const char *__get_key_name(const struct lockdep_subclass_key *key,
char *str);
struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i);
......@@ -137,6 +140,10 @@ extern unsigned int max_bfs_queue_depth;
#ifdef CONFIG_PROVE_LOCKING
extern unsigned long lockdep_count_forward_deps(struct lock_class *);
extern unsigned long lockdep_count_backward_deps(struct lock_class *);
#ifdef CONFIG_TRACE_IRQFLAGS
u64 lockdep_stack_trace_count(void);
u64 lockdep_stack_hash_count(void);
#endif
#else
static inline unsigned long
lockdep_count_forward_deps(struct lock_class *class)
......
......@@ -285,6 +285,12 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
nr_process_chains);
seq_printf(m, " stack-trace entries: %11lu [max: %lu]\n",
nr_stack_trace_entries, MAX_STACK_TRACE_ENTRIES);
#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
seq_printf(m, " number of stack traces: %llu\n",
lockdep_stack_trace_count());
seq_printf(m, " number of stack hash chains: %llu\n",
lockdep_stack_hash_count());
#endif
seq_printf(m, " combined max dependencies: %11u\n",
(nr_hardirq_chains + 1) *
(nr_softirq_chains + 1) *
......@@ -399,7 +405,7 @@ static void seq_lock_time(struct seq_file *m, struct lock_time *lt)
static void seq_stats(struct seq_file *m, struct lock_stat_data *data)
{
struct lockdep_subclass_key *ckey;
const struct lockdep_subclass_key *ckey;
struct lock_class_stats *stats;
struct lock_class *class;
const char *cname;
......
......@@ -65,11 +65,37 @@ EXPORT_SYMBOL(__mutex_init);
#define MUTEX_FLAGS 0x07
/*
* Internal helper function; C doesn't allow us to hide it :/
*
* DO NOT USE (outside of mutex code).
*/
static inline struct task_struct *__mutex_owner(struct mutex *lock)
{
return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
}
static inline struct task_struct *__owner_task(unsigned long owner)
{
return (struct task_struct *)(owner & ~MUTEX_FLAGS);
}
bool mutex_is_locked(struct mutex *lock)
{
return __mutex_owner(lock) != NULL;
}
EXPORT_SYMBOL(mutex_is_locked);
__must_check enum mutex_trylock_recursive_enum
mutex_trylock_recursive(struct mutex *lock)
{
if (unlikely(__mutex_owner(lock) == current))
return MUTEX_TRYLOCK_RECURSIVE;
return mutex_trylock(lock);
}
EXPORT_SYMBOL(mutex_trylock_recursive);
static inline unsigned long __owner_flags(unsigned long owner)
{
return owner & MUTEX_FLAGS;
......
......@@ -105,8 +105,9 @@
#ifdef CONFIG_DEBUG_RWSEMS
# define DEBUG_RWSEMS_WARN_ON(c, sem) do { \
if (!debug_locks_silent && \
WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty\n",\
#c, atomic_long_read(&(sem)->count), \
(unsigned long) sem->magic, \
atomic_long_read(&(sem)->owner), (long)current, \
list_empty(&(sem)->wait_list) ? "" : "not ")) \
debug_locks_off(); \
......@@ -329,6 +330,9 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
*/
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map(&sem->dep_map, name, key, 0);
#endif
#ifdef CONFIG_DEBUG_RWSEMS
sem->magic = sem;
#endif
atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
raw_spin_lock_init(&sem->wait_lock);
......@@ -724,11 +728,12 @@ rwsem_spin_on_owner(struct rw_semaphore *sem, unsigned long nonspinnable)
rcu_read_lock();
for (;;) {
if (atomic_long_read(&sem->count) & RWSEM_FLAG_HANDOFF) {
state = OWNER_NONSPINNABLE;
break;
}
/*
* When a waiting writer set the handoff flag, it may spin
* on the owner as well. Once that writer acquires the lock,
* we can spin on it. So we don't need to quit even when the
* handoff bit is set.
*/
new = rwsem_owner_flags(sem, &new_flags);
if ((new != owner) || (new_flags != flags)) {
state = rwsem_owner_state(new, new_flags, nonspinnable);
......@@ -974,6 +979,13 @@ static inline bool rwsem_reader_phase_trylock(struct rw_semaphore *sem,
{