[PATCH v2 02/19] locking/lockdep: Add sequence counter to held_lock
Liam R. Howlett (Oracle)
liam at infradead.org
Tue Jun 30 12:08:26 PDT 2026
Add an 8 bit small sequence counter to the held_lock struct to detect if
the lock as been dropped and reacquired. This is useful when a data
structure depends on a constant locking context, but is not able to
detect locking and unlocking of the lock through its own API.
Since the __lock_unpin_lock() will no longer detect underflow by casting
the unsigned int to a signed int, update the casting code to use a temp
variable for calculations using a signed int.
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Will Deacon <will at kernel.org>
Cc: Boqun Feng <boqun.feng at gmail.com>
Cc: Waiman Long <longman at redhat.com>
Link: https://lore.kernel.org/all/h3tpnj5kzcrxms5picmimtkpg4aypcpip5wbd6bt2rpdj5k7eb@nhtzs3lefrkq/
Suggested-by: Peter Zijlstra <peterz at infradead.org>
Signed-off-by: Liam R. Howlett (Oracle) <liam at infradead.org>
---
include/linux/lockdep.h | 3 ++
include/linux/lockdep_types.h | 3 +-
include/linux/sched.h | 1 +
kernel/locking/lockdep.c | 58 ++++++++++++++++++++++++++++++-----
4 files changed, 57 insertions(+), 8 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 621566345406d..a6451ecbbe9a0 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -273,6 +273,9 @@ extern struct pin_cookie lock_pin_lock(struct lockdep_map *lock);
extern void lock_repin_lock(struct lockdep_map *lock, struct pin_cookie);
extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
+extern u32 lock_sequence(struct lockdep_map *lock);
+#define lockdep_sequence(lock) lock_sequence(&(lock)->dep_map)
+
#define lockdep_depth(tsk) (debug_locks ? (tsk)->lockdep_depth : 0)
#define lockdep_assert(cond) \
diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
index eae115a264885..55c4b152fedf7 100644
--- a/include/linux/lockdep_types.h
+++ b/include/linux/lockdep_types.h
@@ -253,7 +253,8 @@ struct held_lock {
unsigned int hardirqs_off:1;
unsigned int sync:1;
unsigned int references:11; /* 32 bits */
- unsigned int pin_count;
+ unsigned int pin_count:24;
+ unsigned int seq_count:8;
};
#else /* !CONFIG_LOCKDEP */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 373bcc0598d10..14d5ce8dd6136 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1288,6 +1288,7 @@ struct task_struct {
u64 curr_chain_key;
int lockdep_depth;
unsigned int lockdep_recursion;
+ unsigned int lockdep_seq;
struct held_lock held_locks[MAX_LOCK_DEPTH];
#endif
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2d4c5bab5af88..a69567bdd7912 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5077,7 +5077,7 @@ static int __lock_is_held(const struct lockdep_map *lock, int read);
static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
int trylock, int read, int check, int hardirqs_off,
struct lockdep_map *nest_lock, unsigned long ip,
- int references, int pin_count, int sync)
+ int references, int pin_count, int sync, int seq)
{
struct task_struct *curr = current;
struct lock_class *class = NULL;
@@ -5183,6 +5183,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
hlock->holdtime_stamp = lockstat_clock();
#endif
hlock->pin_count = pin_count;
+ hlock->seq_count = seq;
if (check_wait_context(curr, hlock))
return 0;
@@ -5388,7 +5389,7 @@ static int reacquire_held_locks(struct task_struct *curr, unsigned int depth,
hlock->read, hlock->check,
hlock->hardirqs_off,
hlock->nest_lock, hlock->acquire_ip,
- hlock->references, hlock->pin_count, 0)) {
+ hlock->references, hlock->pin_count, 0, hlock->seq_count)) {
case 0:
return 1;
case 1:
@@ -5669,14 +5670,17 @@ static void __lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie
struct held_lock *hlock = curr->held_locks + i;
if (match_held_lock(hlock, lock)) {
+ int pin_count;
+
if (WARN(!hlock->pin_count, "unpinning an unpinned lock\n"))
return;
- hlock->pin_count -= cookie.val;
+ pin_count = hlock->pin_count - cookie.val;
- if (WARN((int)hlock->pin_count < 0, "pin count corrupted\n"))
- hlock->pin_count = 0;
+ if (WARN(pin_count < 0, "pin count corrupted\n"))
+ pin_count = 0;
+ hlock->pin_count = pin_count;
return;
}
}
@@ -5684,6 +5688,24 @@ static void __lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie
WARN(1, "unpinning an unheld lock\n");
}
+static u32 __lock_sequence(struct lockdep_map *lock)
+{
+ struct task_struct *curr = current;
+ int i;
+
+ if (unlikely(!debug_locks))
+ return ~0;
+
+ for (i = 0; i < curr->lockdep_depth; i++) {
+ struct held_lock *hlock = curr->held_locks + i;
+
+ if (match_held_lock(hlock, lock))
+ return hlock->seq_count;
+ }
+
+ return ~0;
+}
+
/*
* Check whether we follow the irq-flags state precisely:
*/
@@ -5866,7 +5888,8 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
lockdep_recursion_inc();
__lock_acquire(lock, subclass, trylock, read, check,
- irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 0);
+ irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 0,
+ ++current->lockdep_seq);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
}
@@ -5914,7 +5937,8 @@ void lock_sync(struct lockdep_map *lock, unsigned subclass, int read,
lockdep_recursion_inc();
__lock_acquire(lock, subclass, 0, read, check,
- irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 1);
+ irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 1,
+ ++current->lockdep_seq);
check_chain_key(current);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -6000,6 +6024,26 @@ void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
}
EXPORT_SYMBOL_GPL(lock_unpin_lock);
+u32 lock_sequence(struct lockdep_map *lock)
+{
+ unsigned long flags;
+ u32 seq = ~0;
+
+ if (unlikely(!lockdep_enabled()))
+ return seq;
+
+ raw_local_irq_save(flags);
+ check_flags(flags);
+
+ lockdep_recursion_inc();
+ seq = __lock_sequence(lock);
+ lockdep_recursion_finish();
+ raw_local_irq_restore(flags);
+
+ return seq;
+}
+EXPORT_SYMBOL_GPL(lock_sequence);
+
#ifdef CONFIG_LOCK_STAT
static void print_lock_contention_bug(struct task_struct *curr,
struct lockdep_map *lock,
--
2.47.3
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