On Fri, 2008-08-01 at 16:26 -0700, Linus Torvalds wrote: > On Fri, 1 Aug 2008, David Miller wrote: > > > > Taking more than a few locks of the same class at once is bad > > news and it's better to find an alternative method. > > It's not always wrong. > > If you can guarantee that anybody that takes more than one lock of a > particular class will always take a single top-level lock _first_, then > that's all good. You can obviously screw up and take the same lock _twice_ > (which will deadlock), but at least you cannot get into ABBA situations. > > So maybe the right thing to do is to just teach lockdep about "lock > protection locks". That would have solved the multi-queue issues for > networking too - all the actual network drivers would still have taken > just their single queue lock, but the one case that needs to take all of > them would have taken a separate top-level lock first. > > Never mind that the multi-queue locks were always taken in the same order: > it's never wrong to just have some top-level serialization, and anybody > who needs to take locks might as well do , because they sure as > hell aren't going to be on _any_ fastpaths. > > So the simplest solution really sounds like just teaching lockdep about > that one special case. It's not "nesting" exactly, although it's obviously > related to it. Do as Linus suggested. The lock protection lock is called nest_lock. Note that we still have the MAX_LOCK_DEPTH (48) limit to consider, so anything that spills that it still up shit creek. Signed-off-by: Peter Zijlstra --- include/linux/lockdep.h | 34 ++++++++++++++++++---------------- include/linux/rcuclassic.h | 2 +- kernel/lockdep.c | 26 +++++++++++++++++++++----- 3 files changed, 40 insertions(+), 22 deletions(-) Index: linux-2.6/kernel/lockdep.c =================================================================== --- linux-2.6.orig/kernel/lockdep.c +++ linux-2.6/kernel/lockdep.c @@ -1372,18 +1372,32 @@ check_deadlock(struct task_struct *curr, struct lockdep_map *next_instance, int read) { struct held_lock *prev; + struct held_lock *nest = NULL; int i; for (i = 0; i < curr->lockdep_depth; i++) { prev = curr->held_locks + i; + + if (prev->instance == next->nest_lock) + nest = prev; + if (hlock_class(prev) != hlock_class(next)) continue; + /* * Allow read-after-read recursion of the same * lock class (i.e. read_lock(lock)+read_lock(lock)): */ if ((read == 2) && prev->read) return 2; + + /* + * We're holding the nest_lock, which serializes this lock's + * nesting behaviour. + */ + if (nest) + return 2; + return print_deadlock_bug(curr, prev, next); } return 1; @@ -2507,7 +2521,7 @@ EXPORT_SYMBOL_GPL(lockdep_init_map); */ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass, int trylock, int read, int check, int hardirqs_off, - unsigned long ip) + struct lockdep_map *nest_lock, unsigned long ip) { struct task_struct *curr = current; struct lock_class *class = NULL; @@ -2566,6 +2580,7 @@ static int __lock_acquire(struct lockdep hlock->class_idx = class - lock_classes + 1; hlock->acquire_ip = ip; hlock->instance = lock; + hlock->nest_lock = nest_lock; hlock->trylock = trylock; hlock->read = read; hlock->check = check; @@ -2717,7 +2732,7 @@ found_it: if (!__lock_acquire(hlock->instance, hlock_class(hlock)->subclass, hlock->trylock, hlock->read, hlock->check, hlock->hardirqs_off, - hlock->acquire_ip)) + hlock->nest_lock, hlock->acquire_ip)) return 0; } @@ -2778,7 +2793,7 @@ found_it: if (!__lock_acquire(hlock->instance, hlock_class(hlock)->subclass, hlock->trylock, hlock->read, hlock->check, hlock->hardirqs_off, - hlock->acquire_ip)) + hlock->nest_lock, hlock->acquire_ip)) return 0; } @@ -2915,7 +2930,8 @@ EXPORT_SYMBOL_GPL(lock_set_subclass); * and also avoid lockdep recursion: */ void lock_acquire(struct lockdep_map *lock, unsigned int subclass, - int trylock, int read, int check, unsigned long ip) + int trylock, int read, int check, + struct lockdep_map *nest_lock, unsigned long ip) { unsigned long flags; @@ -2930,7 +2946,7 @@ void lock_acquire(struct lockdep_map *lo current->lockdep_recursion = 1; __lock_acquire(lock, subclass, trylock, read, check, - irqs_disabled_flags(flags), ip); + irqs_disabled_flags(flags), nest_lock, ip); current->lockdep_recursion = 0; raw_local_irq_restore(flags); } Index: linux-2.6/include/linux/lockdep.h =================================================================== --- linux-2.6.orig/include/linux/lockdep.h +++ linux-2.6/include/linux/lockdep.h @@ -211,6 +211,7 @@ struct held_lock { u64 prev_chain_key; unsigned long acquire_ip; struct lockdep_map *instance; + struct lockdep_map *nest_lock; #ifdef CONFIG_LOCK_STAT u64 waittime_stamp; u64 holdtime_stamp; @@ -297,7 +298,8 @@ extern void lockdep_init_map(struct lock * 2: full validation */ extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass, - int trylock, int read, int check, unsigned long ip); + int trylock, int read, int check, + struct lockdep_map *nest_lock, unsigned long ip); extern void lock_release(struct lockdep_map *lock, int nested, unsigned long ip); @@ -319,7 +321,7 @@ static inline void lockdep_on(void) { } -# define lock_acquire(l, s, t, r, c, i) do { } while (0) +# define lock_acquire(l, s, t, r, c, n, i) do { } while (0) # define lock_release(l, n, i) do { } while (0) # define lock_set_subclass(l, s, i) do { } while (0) # define lockdep_init() do { } while (0) @@ -407,9 +409,9 @@ static inline void print_irqtrace_events #ifdef CONFIG_DEBUG_LOCK_ALLOC # ifdef CONFIG_PROVE_LOCKING -# define spin_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, i) +# define spin_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, NULL, i) # else -# define spin_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, i) +# define spin_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, NULL, i) # endif # define spin_release(l, n, i) lock_release(l, n, i) #else @@ -419,11 +421,11 @@ static inline void print_irqtrace_events #ifdef CONFIG_DEBUG_LOCK_ALLOC # ifdef CONFIG_PROVE_LOCKING -# define rwlock_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, i) -# define rwlock_acquire_read(l, s, t, i) lock_acquire(l, s, t, 2, 2, i) +# define rwlock_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, NULL, i) +# define rwlock_acquire_read(l, s, t, i) lock_acquire(l, s, t, 2, 2, NULL, i) # else -# define rwlock_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, i) -# define rwlock_acquire_read(l, s, t, i) lock_acquire(l, s, t, 2, 1, i) +# define rwlock_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, NULL, i) +# define rwlock_acquire_read(l, s, t, i) lock_acquire(l, s, t, 2, 1, NULL, i) # endif # define rwlock_release(l, n, i) lock_release(l, n, i) #else @@ -434,9 +436,9 @@ static inline void print_irqtrace_events #ifdef CONFIG_DEBUG_LOCK_ALLOC # ifdef CONFIG_PROVE_LOCKING -# define mutex_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, i) +# define mutex_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, NULL, i) # else -# define mutex_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, i) +# define mutex_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, NULL, i) # endif # define mutex_release(l, n, i) lock_release(l, n, i) #else @@ -446,11 +448,11 @@ static inline void print_irqtrace_events #ifdef CONFIG_DEBUG_LOCK_ALLOC # ifdef CONFIG_PROVE_LOCKING -# define rwsem_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, i) -# define rwsem_acquire_read(l, s, t, i) lock_acquire(l, s, t, 1, 2, i) +# define rwsem_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 2, NULL, i) +# define rwsem_acquire_read(l, s, t, i) lock_acquire(l, s, t, 1, 2, NULL, i) # else -# define rwsem_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, i) -# define rwsem_acquire_read(l, s, t, i) lock_acquire(l, s, t, 1, 1, i) +# define rwsem_acquire(l, s, t, i) lock_acquire(l, s, t, 0, 1, NULL, i) +# define rwsem_acquire_read(l, s, t, i) lock_acquire(l, s, t, 1, 1, NULL, i) # endif # define rwsem_release(l, n, i) lock_release(l, n, i) #else @@ -461,9 +463,9 @@ static inline void print_irqtrace_events #ifdef CONFIG_DEBUG_LOCK_ALLOC # ifdef CONFIG_PROVE_LOCKING -# define map_acquire(l) lock_acquire(l, 0, 0, 0, 2, _THIS_IP_) +# define map_acquire(l) lock_acquire(l, 0, 0, 0, 2, NULL, _THIS_IP_) # else -# define map_acquire(l) lock_acquire(l, 0, 0, 0, 1, _THIS_IP_) +# define map_acquire(l) lock_acquire(l, 0, 0, 0, 1, NULL, _THIS_IP_) # endif # define map_release(l) lock_release(l, 1, _THIS_IP_) #else Index: linux-2.6/include/linux/rcuclassic.h =================================================================== --- linux-2.6.orig/include/linux/rcuclassic.h +++ linux-2.6/include/linux/rcuclassic.h @@ -117,7 +117,7 @@ extern int rcu_needs_cpu(int cpu); #ifdef CONFIG_DEBUG_LOCK_ALLOC extern struct lockdep_map rcu_lock_map; # define rcu_read_acquire() \ - lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_) + lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) #else # define rcu_read_acquire() do { } while (0) -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/