| Message ID | 20230113235722.1226525-1-boqun.feng@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 24bd2cbb49433aa3424b9dd67bbf40f0e66bae15 |
| Headers | show |
| Series | Detect SRCU related deadlocks | expand |
On 1/13/23 18:57, Boqun Feng wrote: > 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> > --- > 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 ba09df6a0872..febd7ecc225c 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 cffa026a765f..4031d87f6829 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1880,6 +1880,8 @@ 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 > @@ -1907,7 +1909,10 @@ 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("); > @@ -1916,7 +1921,12 @@ 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"); src can be sync() but not the target. Is there a reason why that is the case? > @@ -4530,7 +4540,13 @@ 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)) > @@ -4909,7 +4925,7 @@ 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; > @@ -4960,7 +4976,8 @@ 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) > @@ -4994,6 +5011,7 @@ 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 > @@ -5055,6 +5073,10 @@ 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); Even with sync, there is still a corresponding lock_acquire() and lock_release(), you can't exit here without increasing lockdep_depth. That can cause underflow. Cheers, Longman
On Mon, Jan 16, 2023 at 05:21:09PM -0500, Waiman Long wrote: > On 1/13/23 18:57, Boqun Feng wrote: > > 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> > > --- > > 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 ba09df6a0872..febd7ecc225c 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 cffa026a765f..4031d87f6829 100644 > > --- a/kernel/locking/lockdep.c > > +++ b/kernel/locking/lockdep.c > > @@ -1880,6 +1880,8 @@ 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 > > @@ -1907,7 +1909,10 @@ 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("); > > @@ -1916,7 +1921,12 @@ 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"); > > src can be sync() but not the target. Is there a reason why that is the > case? > The functions annotated by sync() don't create real critical sections, so no lock dependency can be created from a sync(), for example: synchronize_srcu(A); mutex_lock(B); no dependency from A to B. In the scenario case, if we see a dependency target -> source, the target cannot be a lock_sync(). I will add better documentation later. > > > @@ -4530,7 +4540,13 @@ 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)) > > @@ -4909,7 +4925,7 @@ 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; > > @@ -4960,7 +4976,8 @@ 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) > > @@ -4994,6 +5011,7 @@ 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 > > @@ -5055,6 +5073,10 @@ 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); > > Even with sync, there is still a corresponding lock_acquire() and > lock_release(), you can't exit here without increasing lockdep_depth. That > can cause underflow. > I actually remove the __lock_release() in lock_sync() in this patch, so I think it's OK. But I must admit the whole submission is to give David something to see whether the output is an improvement, so I probably should separate the output changes and the lock_sync() internall into two patches (and the later can also be folded into the introduction patch). Regards, Boqun > Cheers, > Longman >
On 1/16/23 17:35, Boqun Feng wrote: > On Mon, Jan 16, 2023 at 05:21:09PM -0500, Waiman Long wrote: >> On 1/13/23 18:57, Boqun Feng wrote: >>> 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> >>> --- >>> 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 ba09df6a0872..febd7ecc225c 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 cffa026a765f..4031d87f6829 100644 >>> --- a/kernel/locking/lockdep.c >>> +++ b/kernel/locking/lockdep.c >>> @@ -1880,6 +1880,8 @@ 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 >>> @@ -1907,7 +1909,10 @@ 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("); >>> @@ -1916,7 +1921,12 @@ 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"); >> src can be sync() but not the target. Is there a reason why that is the >> case? >> > The functions annotated by sync() don't create real critical sections, > so no lock dependency can be created from a sync(), for example: > > synchronize_srcu(A); > mutex_lock(B); > > no dependency from A to B. In the scenario case, if we see a dependency > target -> source, the target cannot be a lock_sync(). I will add better > documentation later. Right, the dependency won't happen since you reduce lock_sync() to mostly do validate_chain() without actually storing it in the lock chain which I did miss in my initial review. Without that, a dependency may happen if an NMI happens between lock_acquire() and lock_release() in lock_sync(). >>> @@ -4530,7 +4540,13 @@ 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)) >>> @@ -4909,7 +4925,7 @@ 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; >>> @@ -4960,7 +4976,8 @@ 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) >>> @@ -4994,6 +5011,7 @@ 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 >>> @@ -5055,6 +5073,10 @@ 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); >> Even with sync, there is still a corresponding lock_acquire() and >> lock_release(), you can't exit here without increasing lockdep_depth. That >> can cause underflow. >> > I actually remove the __lock_release() in lock_sync() in this patch, so > I think it's OK. But I must admit the whole submission is to give David > something to see whether the output is an improvement, so I probably > should separate the output changes and the lock_sync() internall into > two patches (and the later can also be folded into the introduction > patch). I saw that now. You may not need to separate it into 2 patches since there is some dependency between the two. You do have to document the 2 different changes in your patch description. Cheers, Longman
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h index ba09df6a0872..febd7ecc225c 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 cffa026a765f..4031d87f6829 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -1880,6 +1880,8 @@ 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 @@ -1907,7 +1909,10 @@ 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("); @@ -1916,7 +1921,12 @@ 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"); @@ -4530,7 +4540,13 @@ 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)) @@ -4909,7 +4925,7 @@ 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; @@ -4960,7 +4976,8 @@ 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) @@ -4994,6 +5011,7 @@ 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 @@ -5055,6 +5073,10 @@ 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); @@ -5196,7 +5218,7 @@ 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: @@ -5666,7 +5688,7 @@ 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); } @@ -5699,11 +5721,6 @@ 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 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) @@ -5717,10 +5734,9 @@ 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); }
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> --- include/linux/lockdep.h | 3 ++- kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++-------------- 2 files changed, 34 insertions(+), 17 deletions(-)