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![Waiman Long](/assets/img/avatar_default.png)
Once a lock class is zapped, all the lock chains that include the zapped class are essentially useless. The lock_chain structure itself can be reused, but not the corresponding chain_hlocks[] entries. Over time, we will run out of chain_hlocks entries while there are still plenty of other lockdep array entries available. To fix this imbalance, we have to make chain_hlocks entries reusable just like the others. As the freed chain_hlocks entries are in blocks of various lengths. A simple bitmap like the one used in the other reusable lockdep arrays isn't applicable. Instead the chain_hlocks entries are put into bucketed lists (MAX_CHAIN_BUCKETS) of chain blocks. Bucket 0 is the variable size bucket which houses chain blocks of size larger than MAX_CHAIN_BUCKETS sorted in decreasing size order. Initially, the whole array is in one chain block (the primordial chain block) in bucket 0. The minimum size of a chain block is 2 chain_hlocks entries. That will be the minimum allocation size. In other word, allocation requests for one chain_hlocks entry will cause 2-entry block to be returned and hence 1 entry will be wasted. Allocation requests for the chain_hlocks are fulfilled first by looking for chain block of matching size. If not found, the first chain block from bucket[0] (the largest one) is split. That can cause hlock entries fragmentation and reduce allocation efficiency if a chain block of size > MAX_CHAIN_BUCKETS is ever zapped and put back to after the primordial chain block. So the MAX_CHAIN_BUCKETS must be large enough that this should seldom happen. By reusing the chain_hlocks entries, we are able to handle workloads that add and zap a lot of lock classes without the risk of running out of chain_hlocks entries as long as the total number of outstanding lock classes at any time remain within a reasonable limit. Two new tracking counters, nr_free_chain_hlocks & nr_large_chain_blocks, are added to track the total number of chain_hlocks entries in the free bucketed lists and the number of large chain blocks in buckets[0] respectively. The nr_free_chain_hlocks replaces nr_chain_hlocks. The nr_large_chain_blocks counter enables to see if we should increase the number of buckets (MAX_CHAIN_BUCKETS) available so as to avoid to avoid the fragmentation problem in bucket[0]. An internal nfsd test that ran for more than an hour and kept on loading and unloading kernel modules could cause the following message to be displayed. [ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low! The patched kernel was able to complete the test with a lot of free chain_hlocks entries to spare: # cat /proc/lockdep_stats : dependency chains: 18867 [max: 65536] dependency chain hlocks: 74926 [max: 327680] dependency chain hlocks lost: 0 : zapped classes: 1541 zapped lock chains: 56765 large chain blocks: 1 By changing MAX_CHAIN_BUCKETS to 3 and add a counter for the size of the largest chain block. The system still worked and We got the following lockdep_stats data: dependency chains: 18601 [max: 65536] dependency chain hlocks used: 73133 [max: 327680] dependency chain hlocks lost: 0 : zapped classes: 1541 zapped lock chains: 56702 large chain blocks: 45165 large chain block size: 20165 By running the test again, I was indeed able to cause chain_hlocks entries to get lost: dependency chain hlocks used: 74806 [max: 327680] dependency chain hlocks lost: 575 : large chain blocks: 48737 large chain block size: 7 Due to the fragmentation, it is possible that the "MAX_LOCKDEP_CHAIN_HLOCKS too low!" error can happen even if a lot of of chain_hlocks entries appear to be free. Fortunately, a MAX_CHAIN_BUCKETS value of 16 should be big enough that few variable sized chain blocks, other than the initial one, should ever be present in bucket 0. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20200206152408.24165-7-longman@redhat.com
254 lines
6.9 KiB
C
254 lines
6.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* kernel/lockdep_internals.h
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*
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* Runtime locking correctness validator
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*
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* lockdep subsystem internal functions and variables.
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*/
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/*
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* Lock-class usage-state bits:
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*/
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enum lock_usage_bit {
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#define LOCKDEP_STATE(__STATE) \
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LOCK_USED_IN_##__STATE, \
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LOCK_USED_IN_##__STATE##_READ, \
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LOCK_ENABLED_##__STATE, \
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LOCK_ENABLED_##__STATE##_READ,
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#include "lockdep_states.h"
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#undef LOCKDEP_STATE
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LOCK_USED,
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LOCK_USAGE_STATES
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};
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#define LOCK_USAGE_READ_MASK 1
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#define LOCK_USAGE_DIR_MASK 2
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#define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK))
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/*
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* Usage-state bitmasks:
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*/
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#define __LOCKF(__STATE) LOCKF_##__STATE = (1 << LOCK_##__STATE),
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enum {
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#define LOCKDEP_STATE(__STATE) \
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__LOCKF(USED_IN_##__STATE) \
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__LOCKF(USED_IN_##__STATE##_READ) \
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__LOCKF(ENABLED_##__STATE) \
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__LOCKF(ENABLED_##__STATE##_READ)
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#include "lockdep_states.h"
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#undef LOCKDEP_STATE
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__LOCKF(USED)
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};
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#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE |
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static const unsigned long LOCKF_ENABLED_IRQ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_USED_IN_##__STATE |
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static const unsigned long LOCKF_USED_IN_IRQ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_ENABLED_##__STATE##_READ |
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static const unsigned long LOCKF_ENABLED_IRQ_READ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKDEP_STATE(__STATE) LOCKF_USED_IN_##__STATE##_READ |
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static const unsigned long LOCKF_USED_IN_IRQ_READ =
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#include "lockdep_states.h"
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0;
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#undef LOCKDEP_STATE
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#define LOCKF_ENABLED_IRQ_ALL (LOCKF_ENABLED_IRQ | LOCKF_ENABLED_IRQ_READ)
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#define LOCKF_USED_IN_IRQ_ALL (LOCKF_USED_IN_IRQ | LOCKF_USED_IN_IRQ_READ)
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#define LOCKF_IRQ (LOCKF_ENABLED_IRQ | LOCKF_USED_IN_IRQ)
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#define LOCKF_IRQ_READ (LOCKF_ENABLED_IRQ_READ | LOCKF_USED_IN_IRQ_READ)
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/*
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* CONFIG_LOCKDEP_SMALL is defined for sparc. Sparc requires .text,
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* .data and .bss to fit in required 32MB limit for the kernel. With
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* CONFIG_LOCKDEP we could go over this limit and cause system boot-up problems.
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* So, reduce the static allocations for lockdeps related structures so that
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* everything fits in current required size limit.
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*/
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#ifdef CONFIG_LOCKDEP_SMALL
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/*
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* MAX_LOCKDEP_ENTRIES is the maximum number of lock dependencies
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* we track.
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*
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* We use the per-lock dependency maps in two ways: we grow it by adding
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* every to-be-taken lock to all currently held lock's own dependency
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* table (if it's not there yet), and we check it for lock order
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* conflicts and deadlocks.
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*/
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#define MAX_LOCKDEP_ENTRIES 16384UL
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#define MAX_LOCKDEP_CHAINS_BITS 15
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#define MAX_STACK_TRACE_ENTRIES 262144UL
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#define STACK_TRACE_HASH_SIZE 8192
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#else
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#define MAX_LOCKDEP_ENTRIES 32768UL
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#define MAX_LOCKDEP_CHAINS_BITS 16
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/*
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* Stack-trace: tightly packed array of stack backtrace
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* addresses. Protected by the hash_lock.
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*/
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#define MAX_STACK_TRACE_ENTRIES 524288UL
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#define STACK_TRACE_HASH_SIZE 16384
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#endif
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/*
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* Bit definitions for lock_chain.irq_context
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*/
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#define LOCK_CHAIN_SOFTIRQ_CONTEXT (1 << 0)
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#define LOCK_CHAIN_HARDIRQ_CONTEXT (1 << 1)
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#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)
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#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
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extern struct list_head all_lock_classes;
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extern struct lock_chain lock_chains[];
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#define LOCK_USAGE_CHARS (1+LOCK_USAGE_STATES/2)
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extern void get_usage_chars(struct lock_class *class,
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char usage[LOCK_USAGE_CHARS]);
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extern const char *__get_key_name(const struct lockdep_subclass_key *key,
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char *str);
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struct lock_class *lock_chain_get_class(struct lock_chain *chain, int i);
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extern unsigned long nr_lock_classes;
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extern unsigned long nr_zapped_classes;
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extern unsigned long nr_zapped_lock_chains;
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extern unsigned long nr_list_entries;
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long lockdep_next_lockchain(long i);
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unsigned long lock_chain_count(void);
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extern unsigned long nr_stack_trace_entries;
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extern unsigned int nr_hardirq_chains;
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extern unsigned int nr_softirq_chains;
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extern unsigned int nr_process_chains;
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extern unsigned int nr_free_chain_hlocks;
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extern unsigned int nr_lost_chain_hlocks;
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extern unsigned int nr_large_chain_blocks;
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extern unsigned int max_lockdep_depth;
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extern unsigned int max_bfs_queue_depth;
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#ifdef CONFIG_PROVE_LOCKING
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extern unsigned long lockdep_count_forward_deps(struct lock_class *);
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extern unsigned long lockdep_count_backward_deps(struct lock_class *);
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#ifdef CONFIG_TRACE_IRQFLAGS
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u64 lockdep_stack_trace_count(void);
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u64 lockdep_stack_hash_count(void);
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#endif
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#else
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static inline unsigned long
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lockdep_count_forward_deps(struct lock_class *class)
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{
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return 0;
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}
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static inline unsigned long
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lockdep_count_backward_deps(struct lock_class *class)
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{
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return 0;
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}
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#endif
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#ifdef CONFIG_DEBUG_LOCKDEP
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#include <asm/local.h>
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/*
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* Various lockdep statistics.
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* We want them per cpu as they are often accessed in fast path
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* and we want to avoid too much cache bouncing.
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*/
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struct lockdep_stats {
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unsigned long chain_lookup_hits;
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unsigned int chain_lookup_misses;
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unsigned long hardirqs_on_events;
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unsigned long hardirqs_off_events;
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unsigned long redundant_hardirqs_on;
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unsigned long redundant_hardirqs_off;
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unsigned long softirqs_on_events;
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unsigned long softirqs_off_events;
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unsigned long redundant_softirqs_on;
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unsigned long redundant_softirqs_off;
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int nr_unused_locks;
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unsigned int nr_redundant_checks;
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unsigned int nr_redundant;
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unsigned int nr_cyclic_checks;
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unsigned int nr_find_usage_forwards_checks;
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unsigned int nr_find_usage_backwards_checks;
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/*
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* Per lock class locking operation stat counts
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*/
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unsigned long lock_class_ops[MAX_LOCKDEP_KEYS];
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};
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DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats);
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extern struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
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#define __debug_atomic_inc(ptr) \
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this_cpu_inc(lockdep_stats.ptr);
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#define debug_atomic_inc(ptr) { \
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WARN_ON_ONCE(!irqs_disabled()); \
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__this_cpu_inc(lockdep_stats.ptr); \
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}
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#define debug_atomic_dec(ptr) { \
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WARN_ON_ONCE(!irqs_disabled()); \
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__this_cpu_dec(lockdep_stats.ptr); \
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}
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#define debug_atomic_read(ptr) ({ \
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struct lockdep_stats *__cpu_lockdep_stats; \
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unsigned long long __total = 0; \
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int __cpu; \
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for_each_possible_cpu(__cpu) { \
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__cpu_lockdep_stats = &per_cpu(lockdep_stats, __cpu); \
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__total += __cpu_lockdep_stats->ptr; \
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} \
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__total; \
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})
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static inline void debug_class_ops_inc(struct lock_class *class)
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{
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int idx;
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idx = class - lock_classes;
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__debug_atomic_inc(lock_class_ops[idx]);
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}
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static inline unsigned long debug_class_ops_read(struct lock_class *class)
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{
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int idx, cpu;
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unsigned long ops = 0;
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idx = class - lock_classes;
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for_each_possible_cpu(cpu)
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ops += per_cpu(lockdep_stats.lock_class_ops[idx], cpu);
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return ops;
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}
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#else
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# define __debug_atomic_inc(ptr) do { } while (0)
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# define debug_atomic_inc(ptr) do { } while (0)
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# define debug_atomic_dec(ptr) do { } while (0)
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# define debug_atomic_read(ptr) 0
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# define debug_class_ops_inc(ptr) do { } while (0)
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#endif
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