lockdep

lockdep

  • 커널이 사용하는 lock(spinlock, mutex, semaphore)을 디버깅하기 위해 사용
  • Lock Problem(Dead-Lock)발생 시 경고 출력을 한다. (dmesg로 볼 수 있다.)
  • ww-mutex를 사용하면 deadlock도 회피할 수 있다.
  • 현재 커널은 userspace에서 사용하는 lock도 디버깅할 수 있다.
  • 커널 빌드 시 락 디버깅 옵션을 enable하여 사용한다.

커널 메뉴 설정 방법

Kernel hacking  --->
	Lock Debugging (spinlocks, mutexes, etc...)  --->
		[*] RT Mutex debugging, deadlock detection
		-*- Spinlock and rw-lock debugging: basic checks
		-*- Mutex debugging: basic checks
		[*] Wait/wound mutex debugging: Slowpath testing
		-*- Lock debugging: detect incorrect freeing of live locks
		[*] Lock debugging: prove locking correctness
		[*] Lock usage statistics
		[*] Lock dependency engine debugging
		[*] Sleep inside atomic section checking
		[*] Locking API boot-time self-tests
		<M> torture tests for locking

/proc 디렉토리에 생성되는 항목들

/proc/lockdep
/proc/lockdep_chains
/proc/lockdep_stat
/proc/locks
/proc/lock_stats

/proc/lockdep

all lock classes:
80a1c55c OPS:      19 FD:   50 BD:    2 +.+...: cgroup_mutex
 -> [80a1c6b0] cgroup_idr_lock
 -> [80a1c5b0] css_set_rwsem
 -> [80a30a74] devcgroup_mutex
 -> [80a1cf3c] freezer_mutex
 -> [80a274ac] kernfs_mutex
(...)

/proc/lockdep_chains

all lock chains:
irq_context: 0
[80a1c55c] cgroup_mutex

irq_context: 0
[80a16a3c] resource_lock
(...)

/proc/lockdep_stat

lock-classes:                         1212 [max: 8191]
 direct dependencies:                  4230 [max: 32768]
 indirect dependencies:               13035
 all direct dependencies:             63105
 dependency chains:                    6166 [max: 65536]
 dependency chain hlocks:             18187 [max: 327680]
 in-hardirq chains:                      29
 in-softirq chains:                     261
 in-process chains:                    4580
 stack-trace entries:                 60133 [max: 524288]
 combined max dependencies:        36006660
 hardirq-safe locks:                     28
 hardirq-unsafe locks:                  471
 softirq-safe locks:                     91
 softirq-unsafe locks:                  415
 irq-safe locks:                         97
 irq-unsafe locks:                      471
 hardirq-read-safe locks:                 3
 hardirq-read-unsafe locks:              80
 softirq-read-safe locks:                 9
 softirq-read-unsafe locks:              77
 irq-read-safe locks:                    10
 irq-read-unsafe locks:                  80
 uncategorized locks:                   130
 unused locks:                            1
 max locking depth:                      15
 max bfs queue depth:                   159
 chain lookup misses:                  6175
 chain lookup hits:                10136672
 cyclic checks:                        4705
 find-mask forwards checks:            1593
 find-mask backwards checks:          31551
 hardirq on events:                 8784803
 hardirq off events:                8784808
 redundant hardirq ons:              356471
 redundant hardirq offs:            6574108
 softirq on events:                  116537
 softirq off events:                 116565
 redundant softirq ons:                   0
 redundant softirq offs:                  0
 debug_locks:                             1

/proc/locks

1: FLOCK  ADVISORY  WRITE 2057 00:0e:7200 0 EOF
2: FLOCK  ADVISORY  WRITE 2246 00:0e:7097 0 EOF

/proc/lock_stat

lock_stat version 0.4
-----------------------------------------------------------------------------------------------------
               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total 
-----------------------------------------------------------------------------------------------------

 &mapping->i_mmap_rwsem-W:          1630           2186           0.99       64477.45      988876.13 
 &mapping->i_mmap_rwsem-R:             0              0           0.00           0.00           0.00 
 ------------------------
   &mapping->i_mmap_rwsem           1017         [<801343b0>] unlink_file_vma+0x34/0x50
   &mapping->i_mmap_rwsem            319         [<8013448c>] vma_link+0x44/0xbc
   &mapping->i_mmap_rwsem            327         [<80024244>] copy_process.part.44+0x1440/0x17e4
   &mapping->i_mmap_rwsem            523         [<801347cc>] vma_adjust+0x2c8/0x604
 ------------------------
   &mapping->i_mmap_rwsem            274         [<8013448c>] vma_link+0x44/0xbc
   &mapping->i_mmap_rwsem            320         [<80024244>] copy_process.part.44+0x1440/0x17e4
   &mapping->i_mmap_rwsem            603         [<801347cc>] vma_adjust+0x2c8/0x604
   &mapping->i_mmap_rwsem            989         [<801343b0>] unlink_file_vma+0x34/0x50

......................................................................................................
---------------------------------------------------------------------------------------------------------
 waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg
---------------------------------------------------------------------------------------------------------

       452.37          37732         174127           2.19       66922.50     2247589.89          12.91
         0.00             12            727          10.57        3269.64       36358.60          50.01










  
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