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Date: Tue, 13 Jun 2017 09:33:36 +0900
From: Byungchul Park <byungchul.park@....com>
To: peterz@...radead.org, mingo@...nel.org
Cc: tglx@...utronix.de, walken@...gle.com, boqun.feng@...il.com,
kirill@...temov.name, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, akpm@...ux-foundation.org, willy@...radead.org,
npiggin@...il.com, kernel-team@....com
Subject: Re: [PATCH v7 05/16] lockdep: Implement crossrelease feature
On Wed, May 24, 2017 at 05:59:38PM +0900, Byungchul Park wrote:
> Lockdep is a runtime locking correctness validator that detects and
> reports a deadlock or its possibility by checking dependencies between
> locks. It's useful since it does not report just an actual deadlock but
> also the possibility of a deadlock that has not actually happened yet.
> That enables problems to be fixed before they affect real systems.
>
> However, this facility is only applicable to typical locks, such as
> spinlocks and mutexes, which are normally released within the context in
> which they were acquired. However, synchronization primitives like page
> locks or completions, which are allowed to be released in any context,
> also create dependencies and can cause a deadlock. So lockdep should
> track these locks to do a better job. The 'crossrelease' implementation
> makes these primitives also be tracked.
Hello,
I think you need to spend much time to review the patches, but 3 weeks
has passed since I submited. It would be appriciated if you spend more
time on it.
Thank you,
Byungchul
>
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
> include/linux/irqflags.h | 24 ++-
> include/linux/lockdep.h | 111 ++++++++++-
> include/linux/sched.h | 8 +
> kernel/exit.c | 1 +
> kernel/fork.c | 3 +
> kernel/locking/lockdep.c | 474 ++++++++++++++++++++++++++++++++++++++++++++---
> kernel/workqueue.c | 2 +
> lib/Kconfig.debug | 12 ++
> 8 files changed, 601 insertions(+), 34 deletions(-)
>
> diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
> index 5dd1272..c40af8a 100644
> --- a/include/linux/irqflags.h
> +++ b/include/linux/irqflags.h
> @@ -23,10 +23,26 @@
> # define trace_softirq_context(p) ((p)->softirq_context)
> # define trace_hardirqs_enabled(p) ((p)->hardirqs_enabled)
> # define trace_softirqs_enabled(p) ((p)->softirqs_enabled)
> -# define trace_hardirq_enter() do { current->hardirq_context++; } while (0)
> -# define trace_hardirq_exit() do { current->hardirq_context--; } while (0)
> -# define lockdep_softirq_enter() do { current->softirq_context++; } while (0)
> -# define lockdep_softirq_exit() do { current->softirq_context--; } while (0)
> +# define trace_hardirq_enter() \
> +do { \
> + current->hardirq_context++; \
> + crossrelease_hardirq_start(); \
> +} while (0)
> +# define trace_hardirq_exit() \
> +do { \
> + current->hardirq_context--; \
> + crossrelease_hardirq_end(); \
> +} while (0)
> +# define lockdep_softirq_enter() \
> +do { \
> + current->softirq_context++; \
> + crossrelease_softirq_start(); \
> +} while (0)
> +# define lockdep_softirq_exit() \
> +do { \
> + current->softirq_context--; \
> + crossrelease_softirq_end(); \
> +} while (0)
> # define INIT_TRACE_IRQFLAGS .softirqs_enabled = 1,
> #else
> # define trace_hardirqs_on() do { } while (0)
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index c1458fe..d531097 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -155,6 +155,12 @@ struct lockdep_map {
> int cpu;
> unsigned long ip;
> #endif
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> + /*
> + * Whether it's a crosslock.
> + */
> + int cross;
> +#endif
> };
>
> static inline void lockdep_copy_map(struct lockdep_map *to,
> @@ -258,7 +264,61 @@ struct held_lock {
> unsigned int hardirqs_off:1;
> unsigned int references:12; /* 32 bits */
> unsigned int pin_count;
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> + /*
> + * Generation id.
> + *
> + * A value of cross_gen_id will be stored when holding this,
> + * which is globally increased whenever each crosslock is held.
> + */
> + unsigned int gen_id;
> +#endif
> +};
> +
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +#define MAX_XHLOCK_TRACE_ENTRIES 5
> +
> +/*
> + * This is for keeping locks waiting for commit so that true dependencies
> + * can be added at commit step.
> + */
> +struct hist_lock {
> + /*
> + * Seperate stack_trace data. This will be used at commit step.
> + */
> + struct stack_trace trace;
> + unsigned long trace_entries[MAX_XHLOCK_TRACE_ENTRIES];
> +
> + /*
> + * Seperate hlock instance. This will be used at commit step.
> + *
> + * TODO: Use a smaller data structure containing only necessary
> + * data. However, we should make lockdep code able to handle the
> + * smaller one first.
> + */
> + struct held_lock hlock;
> +};
> +
> +/*
> + * To initialize a lock as crosslock, lockdep_init_map_crosslock() should
> + * be called instead of lockdep_init_map().
> + */
> +struct cross_lock {
> + /*
> + * Seperate hlock instance. This will be used at commit step.
> + *
> + * TODO: Use a smaller data structure containing only necessary
> + * data. However, we should make lockdep code able to handle the
> + * smaller one first.
> + */
> + struct held_lock hlock;
> +};
> +
> +struct lockdep_map_cross {
> + struct lockdep_map map;
> + struct cross_lock xlock;
> };
> +#endif
>
> /*
> * Initialization, self-test and debugging-output methods:
> @@ -282,13 +342,6 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
> struct lock_class_key *key, int subclass);
>
> /*
> - * To initialize a lockdep_map statically use this macro.
> - * Note that _name must not be NULL.
> - */
> -#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
> - { .name = (_name), .key = (void *)(_key), }
> -
> -/*
> * Reinitialize a lock key - for cases where there is special locking or
> * special initialization of locks so that the validator gets the scope
> * of dependencies wrong: they are either too broad (they need a class-split)
> @@ -443,6 +496,50 @@ static inline void lockdep_on(void)
>
> #endif /* !LOCKDEP */
>
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +extern void lockdep_init_map_crosslock(struct lockdep_map *lock,
> + const char *name,
> + struct lock_class_key *key,
> + int subclass);
> +extern void lock_commit_crosslock(struct lockdep_map *lock);
> +
> +#define STATIC_CROSS_LOCKDEP_MAP_INIT(_name, _key) \
> + { .map.name = (_name), .map.key = (void *)(_key), \
> + .map.cross = 1, }
> +
> +/*
> + * To initialize a lockdep_map statically use this macro.
> + * Note that _name must not be NULL.
> + */
> +#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
> + { .name = (_name), .key = (void *)(_key), .cross = 0, }
> +
> +extern void crossrelease_hardirq_start(void);
> +extern void crossrelease_hardirq_end(void);
> +extern void crossrelease_softirq_start(void);
> +extern void crossrelease_softirq_end(void);
> +extern void crossrelease_work_start(void);
> +extern void crossrelease_work_end(void);
> +extern void init_crossrelease_task(struct task_struct *task);
> +extern void free_crossrelease_task(struct task_struct *task);
> +#else
> +/*
> + * To initialize a lockdep_map statically use this macro.
> + * Note that _name must not be NULL.
> + */
> +#define STATIC_LOCKDEP_MAP_INIT(_name, _key) \
> + { .name = (_name), .key = (void *)(_key), }
> +
> +static inline void crossrelease_hardirq_start(void) {}
> +static inline void crossrelease_hardirq_end(void) {}
> +static inline void crossrelease_softirq_start(void) {}
> +static inline void crossrelease_softirq_end(void) {}
> +static inline void crossrelease_work_start(void) {}
> +static inline void crossrelease_work_end(void) {}
> +static inline void init_crossrelease_task(struct task_struct *task) {}
> +static inline void free_crossrelease_task(struct task_struct *task) {}
> +#endif
> +
> #ifdef CONFIG_LOCK_STAT
>
> extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e9c009d..5f6d6f4 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1749,6 +1749,14 @@ struct task_struct {
> struct held_lock held_locks[MAX_LOCK_DEPTH];
> gfp_t lockdep_reclaim_gfp;
> #endif
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +#define MAX_XHLOCKS_NR 64UL
> + struct hist_lock *xhlocks; /* Crossrelease history locks */
> + unsigned int xhlock_idx;
> + unsigned int xhlock_idx_soft; /* For restoring at softirq exit */
> + unsigned int xhlock_idx_hard; /* For restoring at hardirq exit */
> + unsigned int xhlock_idx_work; /* For restoring at work exit */
> +#endif
> #ifdef CONFIG_UBSAN
> unsigned int in_ubsan;
> #endif
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 3076f30..cc56aad 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -883,6 +883,7 @@ void __noreturn do_exit(long code)
> exit_rcu();
> TASKS_RCU(__srcu_read_unlock(&tasks_rcu_exit_srcu, tasks_rcu_i));
>
> + free_crossrelease_task(tsk);
> do_task_dead();
> }
> EXPORT_SYMBOL_GPL(do_exit);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 997ac1d..f9623a0 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -451,6 +451,7 @@ void __init fork_init(void)
> for (i = 0; i < UCOUNT_COUNTS; i++) {
> init_user_ns.ucount_max[i] = max_threads/2;
> }
> + init_crossrelease_task(&init_task);
> }
>
> int __weak arch_dup_task_struct(struct task_struct *dst,
> @@ -1611,6 +1612,7 @@ static __latent_entropy struct task_struct *copy_process(
> p->lockdep_depth = 0; /* no locks held yet */
> p->curr_chain_key = 0;
> p->lockdep_recursion = 0;
> + init_crossrelease_task(p);
> #endif
>
> #ifdef CONFIG_DEBUG_MUTEXES
> @@ -1856,6 +1858,7 @@ static __latent_entropy struct task_struct *copy_process(
> bad_fork_cleanup_perf:
> perf_event_free_task(p);
> bad_fork_cleanup_policy:
> + free_crossrelease_task(p);
> #ifdef CONFIG_NUMA
> mpol_put(p->mempolicy);
> bad_fork_cleanup_threadgroup_lock:
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 2847356..63eb04a 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -55,6 +55,10 @@
> #define CREATE_TRACE_POINTS
> #include <trace/events/lock.h>
>
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +#include <linux/slab.h>
> +#endif
> +
> #ifdef CONFIG_PROVE_LOCKING
> int prove_locking = 1;
> module_param(prove_locking, int, 0644);
> @@ -709,6 +713,18 @@ static int count_matching_names(struct lock_class *new_class)
> return NULL;
> }
>
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +static void cross_init(struct lockdep_map *lock, int cross);
> +static int cross_lock(struct lockdep_map *lock);
> +static int lock_acquire_crosslock(struct held_lock *hlock);
> +static int lock_release_crosslock(struct lockdep_map *lock);
> +#else
> +static inline void cross_init(struct lockdep_map *lock, int cross) {}
> +static inline int cross_lock(struct lockdep_map *lock) { return 0; }
> +static inline int lock_acquire_crosslock(struct held_lock *hlock) { return 2; }
> +static inline int lock_release_crosslock(struct lockdep_map *lock) { return 2; }
> +#endif
> +
> /*
> * Register a lock's class in the hash-table, if the class is not present
> * yet. Otherwise we look it up. We cache the result in the lock object
> @@ -1768,6 +1784,9 @@ static inline void inc_chains(void)
> if (nest)
> return 2;
>
> + if (cross_lock(prev->instance))
> + continue;
> +
> return print_deadlock_bug(curr, prev, next);
> }
> return 1;
> @@ -1921,30 +1940,36 @@ static inline void inc_chains(void)
> int distance = curr->lockdep_depth - depth + 1;
> hlock = curr->held_locks + depth - 1;
> /*
> - * Only non-recursive-read entries get new dependencies
> - * added:
> + * Only non-crosslock entries get new dependencies added.
> + * Crosslock entries will be added by commit later:
> */
> - if (hlock->read != 2 && hlock->check) {
> - int ret = check_prev_add(curr, hlock, next,
> - distance, &trace, save);
> - if (!ret)
> - return 0;
> -
> + if (!cross_lock(hlock->instance)) {
> /*
> - * Stop saving stack_trace if save_trace() was
> - * called at least once:
> + * Only non-recursive-read entries get new dependencies
> + * added:
> */
> - if (save && ret == 2)
> - save = NULL;
> + if (hlock->read != 2 && hlock->check) {
> + int ret = check_prev_add(curr, hlock, next,
> + distance, &trace, save);
> + if (!ret)
> + return 0;
>
> - /*
> - * Stop after the first non-trylock entry,
> - * as non-trylock entries have added their
> - * own direct dependencies already, so this
> - * lock is connected to them indirectly:
> - */
> - if (!hlock->trylock)
> - break;
> + /*
> + * Stop saving stack_trace if save_trace() was
> + * called at least once:
> + */
> + if (save && ret == 2)
> + save = NULL;
> +
> + /*
> + * Stop after the first non-trylock entry,
> + * as non-trylock entries have added their
> + * own direct dependencies already, so this
> + * lock is connected to them indirectly:
> + */
> + if (!hlock->trylock)
> + break;
> + }
> }
> depth--;
> /*
> @@ -3203,7 +3228,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
> /*
> * Initialize a lock instance's lock-class mapping info:
> */
> -void lockdep_init_map(struct lockdep_map *lock, const char *name,
> +static void __lockdep_init_map(struct lockdep_map *lock, const char *name,
> struct lock_class_key *key, int subclass)
> {
> int i;
> @@ -3261,8 +3286,25 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
> raw_local_irq_restore(flags);
> }
> }
> +
> +void lockdep_init_map(struct lockdep_map *lock, const char *name,
> + struct lock_class_key *key, int subclass)
> +{
> + cross_init(lock, 0);
> + __lockdep_init_map(lock, name, key, subclass);
> +}
> EXPORT_SYMBOL_GPL(lockdep_init_map);
>
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +void lockdep_init_map_crosslock(struct lockdep_map *lock, const char *name,
> + struct lock_class_key *key, int subclass)
> +{
> + cross_init(lock, 1);
> + __lockdep_init_map(lock, name, key, subclass);
> +}
> +EXPORT_SYMBOL_GPL(lockdep_init_map_crosslock);
> +#endif
> +
> struct lock_class_key __lockdep_no_validate__;
> EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
>
> @@ -3317,6 +3359,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
> unsigned int depth;
> int chain_head = 0;
> int class_idx;
> + int ret;
> u64 chain_key;
>
> if (unlikely(!debug_locks))
> @@ -3366,7 +3409,8 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
>
> class_idx = class - lock_classes + 1;
>
> - if (depth) {
> + /* TODO: nest_lock is not implemented for crosslock yet. */
> + if (depth && !cross_lock(lock)) {
> hlock = curr->held_locks + depth - 1;
> if (hlock->class_idx == class_idx && nest_lock) {
> if (hlock->references)
> @@ -3447,6 +3491,14 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
> if (!validate_chain(curr, lock, hlock, chain_head, chain_key))
> return 0;
>
> + ret = lock_acquire_crosslock(hlock);
> + /*
> + * 2 means normal acquire operations are needed. Otherwise, it's
> + * ok just to return with '0:fail, 1:success'.
> + */
> + if (ret != 2)
> + return ret;
> +
> curr->curr_chain_key = chain_key;
> curr->lockdep_depth++;
> check_chain_key(curr);
> @@ -3610,11 +3662,19 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
> struct task_struct *curr = current;
> struct held_lock *hlock, *prev_hlock;
> unsigned int depth;
> - int i;
> + int ret, i;
>
> if (unlikely(!debug_locks))
> return 0;
>
> + ret = lock_release_crosslock(lock);
> + /*
> + * 2 means normal release operations are needed. Otherwise, it's
> + * ok just to return with '0:fail, 1:success'.
> + */
> + if (ret != 2)
> + return ret;
> +
> depth = curr->lockdep_depth;
> /*
> * So we're all set to release this lock.. wait what lock? We don't
> @@ -4557,3 +4617,371 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
> dump_stack();
> }
> EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
> +
> +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> +
> +#define xhlock(i) (current->xhlocks[(i) % MAX_XHLOCKS_NR])
> +
> +/*
> + * Whenever a crosslock is held, cross_gen_id will be increased.
> + */
> +static atomic_t cross_gen_id; /* Can be wrapped */
> +
> +void crossrelease_hardirq_start(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx_hard = current->xhlock_idx;
> +}
> +
> +void crossrelease_hardirq_end(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx = current->xhlock_idx_hard;
> +}
> +
> +void crossrelease_softirq_start(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx_soft = current->xhlock_idx;
> +}
> +
> +void crossrelease_softirq_end(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx = current->xhlock_idx_soft;
> +}
> +
> +/*
> + * Each work of workqueue might run in a different context,
> + * thanks to concurrency support of workqueue. So we have to
> + * distinguish each work to avoid false positive.
> + */
> +void crossrelease_work_start(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx_work = current->xhlock_idx;
> +}
> +
> +void crossrelease_work_end(void)
> +{
> + if (current->xhlocks)
> + current->xhlock_idx = current->xhlock_idx_work;
> +}
> +
> +static int cross_lock(struct lockdep_map *lock)
> +{
> + return lock ? lock->cross : 0;
> +}
> +
> +/*
> + * This is needed to decide the relationship between wrapable variables.
> + */
> +static inline int before(unsigned int a, unsigned int b)
> +{
> + return (int)(a - b) < 0;
> +}
> +
> +static inline struct lock_class *xhlock_class(struct hist_lock *xhlock)
> +{
> + return hlock_class(&xhlock->hlock);
> +}
> +
> +static inline struct lock_class *xlock_class(struct cross_lock *xlock)
> +{
> + return hlock_class(&xlock->hlock);
> +}
> +
> +/*
> + * Should we check a dependency with previous one?
> + */
> +static inline int depend_before(struct held_lock *hlock)
> +{
> + return hlock->read != 2 && hlock->check && !hlock->trylock;
> +}
> +
> +/*
> + * Should we check a dependency with next one?
> + */
> +static inline int depend_after(struct held_lock *hlock)
> +{
> + return hlock->read != 2 && hlock->check;
> +}
> +
> +/*
> + * Check if the xhlock is valid, which would be false if,
> + *
> + * 1. Has not used after initializaion yet.
> + *
> + * Remind hist_lock is implemented as a ring buffer.
> + */
> +static inline int xhlock_valid(struct hist_lock *xhlock)
> +{
> + /*
> + * xhlock->hlock.instance must be !NULL.
> + */
> + return !!xhlock->hlock.instance;
> +}
> +
> +/*
> + * Record a hist_lock entry.
> + *
> + * Irq disable is only required.
> + */
> +static void add_xhlock(struct held_lock *hlock)
> +{
> + unsigned int idx = ++current->xhlock_idx;
> + struct hist_lock *xhlock = &xhlock(idx);
> +
> +#ifdef CONFIG_DEBUG_LOCKDEP
> + /*
> + * This can be done locklessly because they are all task-local
> + * state, we must however ensure IRQs are disabled.
> + */
> + WARN_ON_ONCE(!irqs_disabled());
> +#endif
> +
> + /* Initialize hist_lock's members */
> + xhlock->hlock = *hlock;
> +
> + xhlock->trace.nr_entries = 0;
> + xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES;
> + xhlock->trace.entries = xhlock->trace_entries;
> + xhlock->trace.skip = 3;
> + save_stack_trace(&xhlock->trace);
> +}
> +
> +static inline int same_context_xhlock(struct hist_lock *xhlock)
> +{
> + return xhlock->hlock.irq_context == task_irq_context(current);
> +}
> +
> +/*
> + * This should be lockless as far as possible because this would be
> + * called very frequently.
> + */
> +static void check_add_xhlock(struct held_lock *hlock)
> +{
> + /*
> + * Record a hist_lock, only in case that acquisitions ahead
> + * could depend on the held_lock. For example, if the held_lock
> + * is trylock then acquisitions ahead never depends on that.
> + * In that case, we don't need to record it. Just return.
> + */
> + if (!current->xhlocks || !depend_before(hlock))
> + return;
> +
> + add_xhlock(hlock);
> +}
> +
> +/*
> + * For crosslock.
> + */
> +static int add_xlock(struct held_lock *hlock)
> +{
> + struct cross_lock *xlock;
> + unsigned int gen_id;
> +
> + if (!graph_lock())
> + return 0;
> +
> + xlock = &((struct lockdep_map_cross *)hlock->instance)->xlock;
> +
> + gen_id = (unsigned int)atomic_inc_return(&cross_gen_id);
> + xlock->hlock = *hlock;
> + xlock->hlock.gen_id = gen_id;
> + graph_unlock();
> +
> + return 1;
> +}
> +
> +/*
> + * Called for both normal and crosslock acquires. Normal locks will be
> + * pushed on the hist_lock queue. Cross locks will record state and
> + * stop regular lock_acquire() to avoid being placed on the held_lock
> + * stack.
> + *
> + * Return: 0 - failure;
> + * 1 - crosslock, done;
> + * 2 - normal lock, continue to held_lock[] ops.
> + */
> +static int lock_acquire_crosslock(struct held_lock *hlock)
> +{
> + /*
> + * CONTEXT 1 CONTEXT 2
> + * --------- ---------
> + * lock A (cross)
> + * X = atomic_inc_return(&cross_gen_id)
> + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> + * Y = atomic_read_acquire(&cross_gen_id)
> + * lock B
> + *
> + * atomic_read_acquire() is for ordering between A and B,
> + * IOW, A happens before B, when CONTEXT 2 see Y >= X.
> + *
> + * Pairs with atomic_inc_return() in add_xlock().
> + */
> + hlock->gen_id = (unsigned int)atomic_read_acquire(&cross_gen_id);
> +
> + if (cross_lock(hlock->instance))
> + return add_xlock(hlock);
> +
> + check_add_xhlock(hlock);
> + return 2;
> +}
> +
> +static int copy_trace(struct stack_trace *trace)
> +{
> + unsigned long *buf = stack_trace + nr_stack_trace_entries;
> + unsigned int max_nr = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
> + unsigned int nr = min(max_nr, trace->nr_entries);
> +
> + trace->nr_entries = nr;
> + memcpy(buf, trace->entries, nr * sizeof(trace->entries[0]));
> + trace->entries = buf;
> + nr_stack_trace_entries += nr;
> +
> + if (nr_stack_trace_entries >= MAX_STACK_TRACE_ENTRIES-1) {
> + if (!debug_locks_off_graph_unlock())
> + return 0;
> +
> + print_lockdep_off("BUG: MAX_STACK_TRACE_ENTRIES too low!");
> + dump_stack();
> +
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> +static int commit_xhlock(struct cross_lock *xlock, struct hist_lock *xhlock)
> +{
> + unsigned int xid, pid;
> + u64 chain_key;
> +
> + xid = xlock_class(xlock) - lock_classes;
> + chain_key = iterate_chain_key((u64)0, xid);
> + pid = xhlock_class(xhlock) - lock_classes;
> + chain_key = iterate_chain_key(chain_key, pid);
> +
> + if (lookup_chain_cache(chain_key))
> + return 1;
> +
> + if (!add_chain_cache_classes(xid, pid, xhlock->hlock.irq_context,
> + chain_key))
> + return 0;
> +
> + if (!check_prev_add(current, &xlock->hlock, &xhlock->hlock, 1,
> + &xhlock->trace, copy_trace))
> + return 0;
> +
> + return 1;
> +}
> +
> +static void commit_xhlocks(struct cross_lock *xlock)
> +{
> + unsigned int cur = current->xhlock_idx;
> + unsigned int i;
> +
> + if (!graph_lock())
> + return;
> +
> + for (i = 0; i < MAX_XHLOCKS_NR; i++) {
> + struct hist_lock *xhlock = &xhlock(cur - i);
> +
> + if (!xhlock_valid(xhlock))
> + break;
> +
> + if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id))
> + break;
> +
> + if (!same_context_xhlock(xhlock))
> + break;
> +
> + /*
> + * commit_xhlock() returns 0 with graph_lock already
> + * released if fail.
> + */
> + if (!commit_xhlock(xlock, xhlock))
> + return;
> + }
> +
> + graph_unlock();
> +}
> +
> +void lock_commit_crosslock(struct lockdep_map *lock)
> +{
> + struct cross_lock *xlock;
> + unsigned long flags;
> +
> + if (unlikely(!debug_locks || current->lockdep_recursion))
> + return;
> +
> + if (!current->xhlocks)
> + return;
> +
> + /*
> + * Do commit hist_locks with the cross_lock, only in case that
> + * the cross_lock could depend on acquisitions after that.
> + *
> + * For example, if the cross_lock does not have the 'check' flag
> + * then we don't need to check dependencies and commit for that.
> + * Just skip it. In that case, of course, the cross_lock does
> + * not depend on acquisitions ahead, either.
> + *
> + * WARNING: Don't do that in add_xlock() in advance. When an
> + * acquisition context is different from the commit context,
> + * invalid(skipped) cross_lock might be accessed.
> + */
> + if (!depend_after(&((struct lockdep_map_cross *)lock)->xlock.hlock))
> + return;
> +
> + raw_local_irq_save(flags);
> + check_flags(flags);
> + current->lockdep_recursion = 1;
> + xlock = &((struct lockdep_map_cross *)lock)->xlock;
> + commit_xhlocks(xlock);
> + current->lockdep_recursion = 0;
> + raw_local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(lock_commit_crosslock);
> +
> +/*
> + * Return: 1 - crosslock, done;
> + * 2 - normal lock, continue to held_lock[] ops.
> + */
> +static int lock_release_crosslock(struct lockdep_map *lock)
> +{
> + return cross_lock(lock) ? 1 : 2;
> +}
> +
> +static void cross_init(struct lockdep_map *lock, int cross)
> +{
> + lock->cross = cross;
> +
> + /*
> + * Crossrelease assumes that the ring buffer size of xhlocks
> + * is aligned with power of 2. So force it on build.
> + */
> + BUILD_BUG_ON(MAX_XHLOCKS_NR & (MAX_XHLOCKS_NR - 1));
> +}
> +
> +void init_crossrelease_task(struct task_struct *task)
> +{
> + task->xhlock_idx = UINT_MAX;
> + task->xhlock_idx_soft = UINT_MAX;
> + task->xhlock_idx_hard = UINT_MAX;
> + task->xhlock_idx_work = UINT_MAX;
> + task->xhlocks = kzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR,
> + GFP_KERNEL);
> +}
> +
> +void free_crossrelease_task(struct task_struct *task)
> +{
> + if (task->xhlocks) {
> + void *tmp = task->xhlocks;
> + /* Diable crossrelease for current */
> + task->xhlocks = NULL;
> + kfree(tmp);
> + }
> +}
> +#endif
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 479d840..2f43ac1 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2092,6 +2092,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
>
> lock_map_acquire_read(&pwq->wq->lockdep_map);
> lock_map_acquire(&lockdep_map);
> + crossrelease_work_start();
> trace_workqueue_execute_start(work);
> worker->current_func(work);
> /*
> @@ -2099,6 +2100,7 @@ static void process_one_work(struct worker *worker, struct work_struct *work)
> * point will only record its address.
> */
> trace_workqueue_execute_end(work);
> + crossrelease_work_end();
> lock_map_release(&lockdep_map);
> lock_map_release(&pwq->wq->lockdep_map);
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index a6c8db1..e584431 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1042,6 +1042,18 @@ config DEBUG_LOCK_ALLOC
> spin_lock_init()/mutex_init()/etc., or whether there is any lock
> held during task exit.
>
> +config LOCKDEP_CROSSRELEASE
> + bool "Lock debugging: make lockdep work for crosslocks"
> + depends on PROVE_LOCKING
> + default n
> + help
> + This makes lockdep work for crosslock which is a lock allowed to
> + be released in a different context from the acquisition context.
> + Normally a lock must be released in the context acquiring the lock.
> + However, relexing this constraint helps synchronization primitives
> + such as page locks or completions can use the lock correctness
> + detector, lockdep.
> +
> config PROVE_LOCKING
> bool "Lock debugging: prove locking correctness"
> depends on DEBUG_KERNEL && TRACE_IRQFLAGS_SUPPORT && STACKTRACE_SUPPORT && LOCKDEP_SUPPORT
> --
> 1.9.1
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