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lockdep: Take read/write status in consideration when generate chainkey

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Currently, the chainkey of a lock chain is a hash sum of the class_idx
of all the held locks, the read/write status are not taken in to
consideration while generating the chainkey. This could result into a
problem, if we have:

	P1()
	{
		read_lock(B);
		lock(A);
	}

	P2()
	{
		lock(A);
		read_lock(B);
	}

	P3()
	{
		lock(A);
		write_lock(B);
	}

, and P1(), P2(), P3() run one by one. And when running P2(), lockdep
detects such a lock chain A -> B is not a deadlock, then it's added in
the chain cache, and then when running P3(), even if it's a deadlock, we
could miss it because of the hit of chain cache. This could be confirmed
by self testcase "chain cached mixed R-L/L-W ".

To resolve this, we use concept "hlock_id" to generate the chainkey, the
hlock_id is a tuple (hlock->class_idx, hlock->read), which fits in a u16
type. With this, the chainkeys are different is the lock sequences have
the same locks but different read/write status.

Besides, since we use "hlock_id" to generate chainkeys, the chain_hlocks
array now store the "hlock_id"s rather than lock_class indexes.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200807074238.1632519-15-boqun.feng@gmail.com
This commit is contained in:
Boqun Feng 2020-08-07 15:42:33 +08:00 committed by Peter Zijlstra
parent d4f200e579
commit f611e8cf98
1 changed files with 35 additions and 18 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

53
kernel/locking/lockdep.c
View file

@ -371,6 +371,21 @@ static struct hlist_head classhash_table[CLASSHASH_SIZE];
static struct hlist_head chainhash_table[CHAINHASH_SIZE]; static struct hlist_head chainhash_table[CHAINHASH_SIZE];
/*
* the id of held_lock
*/
static inline u16 hlock_id(struct held_lock *hlock)
{
BUILD_BUG_ON(MAX_LOCKDEP_KEYS_BITS + 2 > 16);
return (hlock->class_idx | (hlock->read << MAX_LOCKDEP_KEYS_BITS));
}
static inline unsigned int chain_hlock_class_idx(u16 hlock_id)
{
return hlock_id & (MAX_LOCKDEP_KEYS - 1);
}
/* /*
* The hash key of the lock dependency chains is a hash itself too: * The hash key of the lock dependency chains is a hash itself too:
* it's a hash of all locks taken up to that lock, including that lock. * it's a hash of all locks taken up to that lock, including that lock.
@ -3202,7 +3217,10 @@ static inline void free_chain_hlocks(int base, int size)
struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i) struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i)
{ {
return lock_classes + chain_hlocks[chain->base + i]; u16 chain_hlock = chain_hlocks[chain->base + i];
unsigned int class_idx = chain_hlock_class_idx(chain_hlock);
return lock_classes + class_idx - 1;
} }
/* /*
@ -3228,12 +3246,12 @@ static inline int get_first_held_lock(struct task_struct *curr,
/* /*
* Returns the next chain_key iteration * Returns the next chain_key iteration
*/ */
static u64 print_chain_key_iteration(int class_idx, u64 chain_key) static u64 print_chain_key_iteration(u16 hlock_id, u64 chain_key)
{ {
u64 new_chain_key = iterate_chain_key(chain_key, class_idx); u64 new_chain_key = iterate_chain_key(chain_key, hlock_id);
printk(" class_idx:%d -> chain_key:%016Lx", printk(" hlock_id:%d -> chain_key:%016Lx",
class_idx, (unsigned int)hlock_id,
(unsigned long long)new_chain_key); (unsigned long long)new_chain_key);
return new_chain_key; return new_chain_key;
} }
@ -3250,12 +3268,12 @@ print_chain_keys_held_locks(struct task_struct *curr, struct held_lock *hlock_ne
hlock_next->irq_context); hlock_next->irq_context);
for (; i < depth; i++) { for (; i < depth; i++) {
hlock = curr->held_locks + i; hlock = curr->held_locks + i;
chain_key = print_chain_key_iteration(hlock->class_idx, chain_key); chain_key = print_chain_key_iteration(hlock_id(hlock), chain_key);
print_lock(hlock); print_lock(hlock);
} }
print_chain_key_iteration(hlock_next->class_idx, chain_key); print_chain_key_iteration(hlock_id(hlock_next), chain_key);
print_lock(hlock_next); print_lock(hlock_next);
} }
@ -3263,14 +3281,14 @@ static void print_chain_keys_chain(struct lock_chain *chain)
{ {
int i; int i;
u64 chain_key = INITIAL_CHAIN_KEY; u64 chain_key = INITIAL_CHAIN_KEY;
int class_id; u16 hlock_id;
printk("depth: %u\n", chain->depth); printk("depth: %u\n", chain->depth);
for (i = 0; i < chain->depth; i++) { for (i = 0; i < chain->depth; i++) {
class_id = chain_hlocks[chain->base + i]; hlock_id = chain_hlocks[chain->base + i];
chain_key = print_chain_key_iteration(class_id, chain_key); chain_key = print_chain_key_iteration(hlock_id, chain_key);
print_lock_name(lock_classes + class_id); print_lock_name(lock_classes + chain_hlock_class_idx(hlock_id) - 1);
printk("\n"); printk("\n");
} }
} }
@ -3319,7 +3337,7 @@ static int check_no_collision(struct task_struct *curr,
} }
for (j = 0; j < chain->depth - 1; j++, i++) { for (j = 0; j < chain->depth - 1; j++, i++) {
id = curr->held_locks[i].class_idx; id = hlock_id(&curr->held_locks[i]);
if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) { if (DEBUG_LOCKS_WARN_ON(chain_hlocks[chain->base + j] != id)) {
print_collision(curr, hlock, chain); print_collision(curr, hlock, chain);
@ -3368,7 +3386,6 @@ static inline int add_chain_cache(struct task_struct *curr,
struct held_lock *hlock, struct held_lock *hlock,
u64 chain_key) u64 chain_key)
{ {
struct lock_class *class = hlock_class(hlock);
struct hlist_head *hash_head = chainhashentry(chain_key); struct hlist_head *hash_head = chainhashentry(chain_key);
struct lock_chain *chain; struct lock_chain *chain;
int i, j; int i, j;
@ -3411,11 +3428,11 @@ static inline int add_chain_cache(struct task_struct *curr,
chain->base = j; chain->base = j;
for (j = 0; j < chain->depth - 1; j++, i++) { for (j = 0; j < chain->depth - 1; j++, i++) {
int lock_id = curr->held_locks[i].class_idx; int lock_id = hlock_id(curr->held_locks + i);
chain_hlocks[chain->base + j] = lock_id; chain_hlocks[chain->base + j] = lock_id;
} }
chain_hlocks[chain->base + j] = class - lock_classes; chain_hlocks[chain->base + j] = hlock_id(hlock);
hlist_add_head_rcu(&chain->entry, hash_head); hlist_add_head_rcu(&chain->entry, hash_head);
debug_atomic_inc(chain_lookup_misses); debug_atomic_inc(chain_lookup_misses);
inc_chains(chain->irq_context); inc_chains(chain->irq_context);
@ -3602,7 +3619,7 @@ static void check_chain_key(struct task_struct *curr)
if (prev_hlock && (prev_hlock->irq_context != if (prev_hlock && (prev_hlock->irq_context !=
hlock->irq_context)) hlock->irq_context))
chain_key = INITIAL_CHAIN_KEY; chain_key = INITIAL_CHAIN_KEY;
chain_key = iterate_chain_key(chain_key, hlock->class_idx); chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
prev_hlock = hlock; prev_hlock = hlock;
} }
if (chain_key != curr->curr_chain_key) { if (chain_key != curr->curr_chain_key) {
@ -4749,7 +4766,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
chain_key = INITIAL_CHAIN_KEY; chain_key = INITIAL_CHAIN_KEY;
chain_head = 1; chain_head = 1;
} }
chain_key = iterate_chain_key(chain_key, class_idx); chain_key = iterate_chain_key(chain_key, hlock_id(hlock));
if (nest_lock && !__lock_is_held(nest_lock, -1)) { if (nest_lock && !__lock_is_held(nest_lock, -1)) {
print_lock_nested_lock_not_held(curr, hlock, ip); print_lock_nested_lock_not_held(curr, hlock, ip);
@ -5648,7 +5665,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
int i; int i;
for (i = chain->base; i < chain->base + chain->depth; i++) { for (i = chain->base; i < chain->base + chain->depth; i++) {
if (chain_hlocks[i] != class - lock_classes) if (chain_hlock_class_idx(chain_hlocks[i]) != class - lock_classes)
continue; continue;
/* /*
* Each lock class occurs at most once in a lock chain so once * Each lock class occurs at most once in a lock chain so once