Currently, in order to annonate functions like synchronize_srcu() for lockdep, a trick as follow can be used: lock_acquire(); lock_release(); , which indicates synchronize_srcu() acts like an empty critical section that waits for other (read-side) critical sections to finish. This surely can catch some deadlock, but as discussion brought up by Paul Mckenney [1], this could introduce false positives because of irq-safe/unsafe detection. Extra tricks might help this: local_irq_disable(..); lock_acquire(); lock_release(); local_irq_enable(...); But it's better that lockdep could provide an annonation for synchronize_srcu() like functions, so that people won't need to repeat the ugly tricks above. Therefore introduce lock_sync(). It's simply an lock+unlock pair with no irq safe/unsafe deadlock check, since the to-be-annontated functions don't create real critical sections therefore there is no way that irq can create extra dependencies. [1]: https://lore.kernel.org/lkml/20180412021233.ewncg5jjuzjw3x62@tardis/ Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> --- include/linux/lockdep.h | 5 +++++ kernel/locking/lockdep.c | 34 ++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+) diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 1f1099dac3f0..ba09df6a0872 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -268,6 +268,10 @@ extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass, extern void lock_release(struct lockdep_map *lock, unsigned long ip); +extern void lock_sync(struct lockdep_map *lock, unsigned int subclass, + int read, int check, struct lockdep_map *nest_lock, + unsigned long ip); + /* lock_is_held_type() returns */ #define LOCK_STATE_UNKNOWN -1 #define LOCK_STATE_NOT_HELD 0 @@ -555,6 +559,7 @@ do { \ #define lock_map_acquire_read(l) lock_acquire_shared_recursive(l, 0, 0, NULL, _THIS_IP_) #define lock_map_acquire_tryread(l) lock_acquire_shared_recursive(l, 0, 1, NULL, _THIS_IP_) #define lock_map_release(l) lock_release(l, _THIS_IP_) +#define lock_map_sync(l) lock_sync(l, 0, 0, 1, NULL, _THIS_IP_) #ifdef CONFIG_PROVE_LOCKING # define might_lock(lock) \ diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index e3375bc40dad..cffa026a765f 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -5692,6 +5692,40 @@ void lock_release(struct lockdep_map *lock, unsigned long ip) } EXPORT_SYMBOL_GPL(lock_release); +/* + * lock_sync() - A special annotation for synchronize_{s,}rcu()-like API. + * + * No actual critical section is created by the APIs annotated with this: these + * 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 acqurie+release anontation 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) +{ + unsigned long flags; + + if (unlikely(!lockdep_enabled())) + return; + + raw_local_irq_save(flags); + 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); + lockdep_recursion_finish(); + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(lock_sync); + noinstr int lock_is_held_type(const struct lockdep_map *lock, int read) { unsigned long flags; -- 2.38.1
