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 --- include/linux/lockdep.h | 3 ++- kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++-------------- 2 files changed, 34 insertions(+), 17 deletions(-)
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index 14d9dbedc6c1..b32256e9e944 100644 --- a/include/linux/lockdep.h +++ b/include/linux/lockdep.h @@ -134,7 +134,8 @@ struct held_lock { unsigned int read:2; /* see lock_acquire() comment */ unsigned int check:1; /* see lock_acquire() comment */ unsigned int hardirqs_off:1; - unsigned int references:12; /* 32 bits */ + unsigned int sync:1; + unsigned int references:11; /* 32 bits */ unsigned int pin_count; };
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); }