On Tue, Jan 17, 2017 at 04:54:31PM +0100, Peter Zijlstra wrote: > On Fri, Jan 13, 2017 at 07:11:43PM +0900, Byungchul Park wrote: > > What do you think about the following patches doing it? > > I was more thinking about something like so... > > Also, I think I want to muck with struct stack_trace; the members: > max_nr_entries and skip are input arguments to save_stack_trace() and > bloat the structure for no reason. With your approach, save_trace() must be called whenever check_prevs_add() is called, which might be unnecessary. Frankly speaking, I think what I proposed resolved it neatly. Don't you think so? > > --- > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 7c38f8f3d97b..f2df300a96ee 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -430,6 +430,21 @@ static int save_trace(struct stack_trace *trace) > return 1; > } > > +static bool return_trace(struct stack_trace *trace) > +{ > + /* > + * If @trace is the last trace generated by save_trace(), then we can > + * return the entries by simply subtracting @nr_stack_trace_entries > + * again. > + */ > + if (trace->entries != stack_trace + nr_stack_trace_entries - trace->nr_entres) > + return false; > + > + nr_stack_trace_entries -= trace->nr_entries; > + trace->entries = NULL; > + return true; > +} > + > unsigned int nr_hardirq_chains; > unsigned int nr_softirq_chains; > unsigned int nr_process_chains; > @@ -1797,20 +1812,12 @@ static inline void inc_chains(void) > */ > static int > check_prev_add(struct task_struct *curr, struct held_lock *prev, > - struct held_lock *next, int distance, int *stack_saved) > + struct held_lock *next, int distance, struct stack_trace *trace) > { > struct lock_list *entry; > int ret; > struct lock_list this; > struct lock_list *uninitialized_var(target_entry); > - /* > - * Static variable, serialized by the graph_lock(). > - * > - * We use this static variable to save the stack trace in case > - * we call into this function multiple times due to encountering > - * trylocks in the held lock stack. > - */ > - static struct stack_trace trace; > > /* > * Prove that the new <prev> -> <next> dependency would not > @@ -1858,11 +1865,7 @@ static inline void inc_chains(void) > } > } > > - if (!*stack_saved) { > - if (!save_trace(&trace)) > - return 0; > - *stack_saved = 1; > - } > + trace->skip = 1; /* mark used */ > > /* > * Ok, all validations passed, add the new lock > @@ -1870,14 +1873,14 @@ static inline void inc_chains(void) > */ > ret = add_lock_to_list(hlock_class(next), > &hlock_class(prev)->locks_after, > - next->acquire_ip, distance, &trace); > + next->acquire_ip, distance, trace); > > if (!ret) > return 0; > > ret = add_lock_to_list(hlock_class(prev), > &hlock_class(next)->locks_before, > - next->acquire_ip, distance, &trace); > + next->acquire_ip, distance, trace); > if (!ret) > return 0; > > @@ -1885,8 +1888,6 @@ static inline void inc_chains(void) > * Debugging printouts: > */ > if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) { > - /* We drop graph lock, so another thread can overwrite trace. */ > - *stack_saved = 0; > graph_unlock(); > printk("\n new dependency: "); > print_lock_name(hlock_class(prev)); > @@ -1908,10 +1909,15 @@ static inline void inc_chains(void) > static int > check_prevs_add(struct task_struct *curr, struct held_lock *next) > { > + struct stack_trace trace = { .nr_entries = 0, .skip = 0, }; > int depth = curr->lockdep_depth; > - int stack_saved = 0; > struct held_lock *hlock; > > + if (!save_trace(&trace)) > + goto out_bug; > + > + trace.skip = 0; /* abuse to mark usage */ > + > /* > * Debugging checks. > * > @@ -1936,7 +1942,7 @@ static inline void inc_chains(void) > */ > if (hlock->read != 2 && hlock->check) { > if (!check_prev_add(curr, hlock, next, > - distance, &stack_saved)) > + distance, &trace)) > return 0; > /* > * Stop after the first non-trylock entry, > @@ -1962,6 +1968,9 @@ static inline void inc_chains(void) > } > return 1; > out_bug: > + if (trace.nr_entries && !trace.skip) > + return_trace(&trace); > + > if (!debug_locks_off_graph_unlock()) > return 0; > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>