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authorBoqun Feng <boqun.feng@gmail.com>2023-01-13 15:57:22 -0800
committerBoqun Feng <boqun.feng@gmail.com>2023-03-27 11:16:04 -0700
commit0471db447cb7de56bbe2fedd9256b4d2b8ef642a (patch)
tree18e5bd3335b4c8d33427766eff6ab10ee5cbf0b8 /kernel/locking
parent60a1a64ec0c08e02f2cd4372cd3971e9d5eb2b37 (diff)
locking/lockdep: Improve the deadlock scenario print for sync and read lock
Lock scenario print is always a weak spot of lockdep splats. Improvement can be made if we rework the dependency search and the error printing. However without touching the graph search, we can improve a little for the circular deadlock case, since we have the to-be-added lock dependency, and know whether these two locks are read/write/sync. In order to know whether a held_lock is sync or not, a bit was "stolen" from ->references, which reduce our limit for the same lock class nesting from 2^12 to 2^11, and it should still be good enough. Besides, since we now have bit in held_lock for sync, we don't need the "hardirqoffs being 1" trick, and also we can avoid the __lock_release() if we jump out of __lock_acquire() before the held_lock stored. With these changes, a deadlock case evolved with read lock and sync gets a better print-out from: [...] Possible unsafe locking scenario: [...] [...] CPU0 CPU1 [...] ---- ---- [...] lock(srcuA); [...] lock(srcuB); [...] lock(srcuA); [...] lock(srcuB); to [...] Possible unsafe locking scenario: [...] [...] CPU0 CPU1 [...] ---- ---- [...] rlock(srcuA); [...] lock(srcuB); [...] lock(srcuA); [...] sync(srcuB); Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep.c48
1 files changed, 32 insertions, 16 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 3ee3b278789d..dcd1d5bfc1e0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1881,6 +1881,8 @@ print_circular_lock_scenario(struct held_lock *src,
struct lock_class *source = hlock_class(src);
struct lock_class *target = hlock_class(tgt);
struct lock_class *parent = prt->class;
+ int src_read = src->read;
+ int tgt_read = tgt->read;
/*
* A direct locking problem where unsafe_class lock is taken
@@ -1908,7 +1910,10 @@ print_circular_lock_scenario(struct held_lock *src,
printk(" Possible unsafe locking scenario:\n\n");
printk(" CPU0 CPU1\n");
printk(" ---- ----\n");
- printk(" lock(");
+ if (tgt_read != 0)
+ printk(" rlock(");
+ else
+ printk(" lock(");
__print_lock_name(target);
printk(KERN_CONT ");\n");
printk(" lock(");
@@ -1917,7 +1922,12 @@ print_circular_lock_scenario(struct held_lock *src,
printk(" lock(");
__print_lock_name(target);
printk(KERN_CONT ");\n");
- printk(" lock(");
+ if (src_read != 0)
+ printk(" rlock(");
+ else if (src->sync)
+ printk(" sync(");
+ else
+ printk(" lock(");
__print_lock_name(source);
printk(KERN_CONT ");\n");
printk("\n *** DEADLOCK ***\n\n");
@@ -4531,7 +4541,13 @@ mark_usage(struct task_struct *curr, struct held_lock *hlock, int check)
return 0;
}
}
- if (!hlock->hardirqs_off) {
+
+ /*
+ * For lock_sync(), don't mark the ENABLED usage, since lock_sync()
+ * creates no critical section and no extra dependency can be introduced
+ * by interrupts
+ */
+ if (!hlock->hardirqs_off && !hlock->sync) {
if (hlock->read) {
if (!mark_lock(curr, hlock,
LOCK_ENABLED_HARDIRQ_READ))
@@ -4910,7 +4926,7 @@ 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 references, int pin_count, int sync)
{
struct task_struct *curr = current;
struct lock_class *class = NULL;
@@ -4961,7 +4977,8 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
class_idx = class - lock_classes;
- if (depth) { /* we're holding locks */
+ if (depth && !sync) {
+ /* we're holding locks and the new held lock is not a sync */
hlock = curr->held_locks + depth - 1;
if (hlock->class_idx == class_idx && nest_lock) {
if (!references)
@@ -4995,6 +5012,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
hlock->trylock = trylock;
hlock->read = read;
hlock->check = check;
+ hlock->sync = !!sync;
hlock->hardirqs_off = !!hardirqs_off;
hlock->references = references;
#ifdef CONFIG_LOCK_STAT
@@ -5056,6 +5074,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
if (!validate_chain(curr, hlock, chain_head, chain_key))
return 0;
+ /* For lock_sync(), we are done here since no actual critical section */
+ if (hlock->sync)
+ return 1;
+
curr->curr_chain_key = chain_key;
curr->lockdep_depth++;
check_chain_key(curr);
@@ -5197,7 +5219,7 @@ 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)) {
+ hlock->references, hlock->pin_count, 0)) {
case 0:
return 1;
case 1:
@@ -5667,7 +5689,7 @@ 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);
+ irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 0);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
}
@@ -5700,11 +5722,6 @@ EXPORT_SYMBOL_GPL(lock_release);
* APIs are used to wait for one or multiple critical sections (on other CPUs
* or threads), and it means that calling these APIs inside these critical
* sections is potential deadlock.
- *
- * This annotation acts as an acquire+release annotation pair with hardirqoff
- * being 1. Since there's no critical section, no interrupt can create extra
- * dependencies "inside" the annotation, hardirqoff == 1 allows us to avoid
- * false positives.
*/
void lock_sync(struct lockdep_map *lock, unsigned subclass, int read,
int check, struct lockdep_map *nest_lock, unsigned long ip)
@@ -5718,10 +5735,9 @@ void lock_sync(struct lockdep_map *lock, unsigned subclass, int read,
check_flags(flags);
lockdep_recursion_inc();
- __lock_acquire(lock, subclass, 0, read, check, 1, nest_lock, ip, 0, 0);
-
- if (__lock_release(lock, ip))
- check_chain_key(current);
+ __lock_acquire(lock, subclass, 0, read, check,
+ irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 1);
+ check_chain_key(current);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
}