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Commit 5e30025a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull core locking changes from Ingo Molnar:
 "The biggest changes:

   - add lockdep support for seqcount/seqlocks structures, this
     unearthed both bugs and required extra annotation.

   - move the various kernel locking primitives to the new
     kernel/locking/ directory"

* 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (21 commits)
  block: Use u64_stats_init() to initialize seqcounts
  locking/lockdep: Mark __lockdep_count_forward_deps() as static
  lockdep/proc: Fix lock-time avg computation
  locking/doc: Update references to kernel/mutex.c
  ipv6: Fix possible ipv6 seqlock deadlock
  cpuset: Fix potential deadlock w/ set_mems_allowed
  seqcount: Add lockdep functionality to seqcount/seqlock structures
  net: Explicitly initialize u64_stats_sync structures for lockdep
  locking: Move the percpu-rwsem code to kernel/locking/
  locking: Move the lglocks code to kernel/locking/
  locking: Move the rwsem code to kernel/locking/
  locking: Move the rtmutex code to kernel/locking/
  locking: Move the semaphore core to kernel/locking/
  locking: Move the spinlock code to kernel/locking/
  locking: Move the lockdep code to kernel/locking/
  locking: Move the mutex code to kernel/locking/
  hung_task debugging: Add tracepoint to report the hang
  x86/locking/kconfig: Update paravirt spinlock Kconfig description
  lockstat: Report avg wait and hold times
  lockdep, x86/alternatives: Drop ancient lockdep fixup message
  ...
parents 7971e23a 90d3839b

Documentation/DocBook/kernel-locking.tmpl

+1 −1
Original line number Diff line number Diff line
@@ -1958,7 +1958,7 @@ machines due to caching. 
  <chapter id="apiref-mutex">

   <title>Mutex API reference</title>

!Iinclude/linux/mutex.h

!Ekernel/mutex.c

!Ekernel/locking/mutex.c

  </chapter>



  <chapter id="apiref-futex">

Documentation/lockstat.txt

+61 −62
Original line number Diff line number Diff line
@@ -47,15 +47,13 @@ With these hooks we provide the following statistics: 
 wait time min     - shortest (non-0) time we ever had to wait for a lock

           max     - longest time we ever had to wait for a lock

	   total   - total time we spend waiting on this lock

	   avg     - average time spent waiting on this lock

 acq-bounces       - number of lock acquisitions that involved x-cpu data

 acquisitions      - number of times we took the lock

 hold time min     - shortest (non-0) time we ever held the lock

	   max     - longest time we ever held the lock

	   total   - total time this lock was held



From these number various other statistics can be derived, such as:



 hold time average = hold time total / acquisitions

	   avg     - average time this lock was held



These numbers are gathered per lock class, per read/write state (when

applicable).
@@ -84,37 +82,38 @@ Look at the current lock statistics: 


# less /proc/lock_stat



01 lock_stat version 0.3

02 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

03                               class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total

04 -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

01 lock_stat version 0.4

02-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

03                              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total   waittime-avg    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total   holdtime-avg

04-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

05

06                          &mm->mmap_sem-W:           233            538 18446744073708       22924.27      607243.51           1342          45806           1.71        8595.89     1180582.34

07                          &mm->mmap_sem-R:           205            587 18446744073708       28403.36      731975.00           1940         412426           0.58      187825.45     6307502.88

06                         &mm->mmap_sem-W:            46             84           0.26         939.10       16371.53         194.90          47291        2922365           0.16     2220301.69 17464026916.32        5975.99

07                         &mm->mmap_sem-R:            37            100           1.31      299502.61      325629.52        3256.30         212344       34316685           0.10        7744.91    95016910.20           2.77

08                         ---------------

09                            &mm->mmap_sem            487          [<ffffffff8053491f>] do_page_fault+0x466/0x928

10                            &mm->mmap_sem            179          [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d

11                            &mm->mmap_sem            279          [<ffffffff80210a57>] sys_mmap+0x75/0xce

12                            &mm->mmap_sem             76          [<ffffffff802a490b>] sys_munmap+0x32/0x59

09                           &mm->mmap_sem              1          [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280

19                           &mm->mmap_sem             96          [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510

11                           &mm->mmap_sem             34          [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0

12                           &mm->mmap_sem             17          [<ffffffff81127e71>] vm_munmap+0x41/0x80

13                         ---------------

14                            &mm->mmap_sem            270          [<ffffffff80210a57>] sys_mmap+0x75/0xce

15                            &mm->mmap_sem            431          [<ffffffff8053491f>] do_page_fault+0x466/0x928

16                            &mm->mmap_sem            138          [<ffffffff802a490b>] sys_munmap+0x32/0x59

17                            &mm->mmap_sem            145          [<ffffffff802a6200>] sys_mprotect+0xcd/0x21d

14                           &mm->mmap_sem              1          [<ffffffff81046fda>] dup_mmap+0x2a/0x3f0

15                           &mm->mmap_sem             60          [<ffffffff81129e29>] SyS_mprotect+0xe9/0x250

16                           &mm->mmap_sem             41          [<ffffffff815351c4>] __do_page_fault+0x1d4/0x510

17                           &mm->mmap_sem             68          [<ffffffff81113d77>] vm_mmap_pgoff+0x87/0xd0

18

19 ...............................................................................................................................................................................................

19.............................................................................................................................................................................................................................

20

21                              dcache_lock:           621            623           0.52         118.26        1053.02           6745          91930           0.29         316.29      118423.41

22                              -----------

23                              dcache_lock            179          [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54

24                              dcache_lock            113          [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb

25                              dcache_lock             99          [<ffffffff802ca0dc>] d_rehash+0x1b/0x44

26                              dcache_lock            104          [<ffffffff802cbca0>] d_instantiate+0x36/0x8a

27                              -----------

28                              dcache_lock            192          [<ffffffff80378274>] _atomic_dec_and_lock+0x34/0x54

29                              dcache_lock             98          [<ffffffff802ca0dc>] d_rehash+0x1b/0x44

30                              dcache_lock             72          [<ffffffff802cc17b>] d_alloc+0x19a/0x1eb

31                              dcache_lock            112          [<ffffffff802cbca0>] d_instantiate+0x36/0x8a

21                         unix_table_lock:           110            112           0.21          49.24         163.91           1.46          21094          66312           0.12         624.42       31589.81           0.48

22                         ---------------

23                         unix_table_lock             45          [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0

24                         unix_table_lock             47          [<ffffffff8150b111>] unix_release_sock+0x31/0x250

25                         unix_table_lock             15          [<ffffffff8150ca37>] unix_find_other+0x117/0x230

26                         unix_table_lock              5          [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0

27                         ---------------

28                         unix_table_lock             39          [<ffffffff8150b111>] unix_release_sock+0x31/0x250

29                         unix_table_lock             49          [<ffffffff8150ad8e>] unix_create1+0x16e/0x1b0

30                         unix_table_lock             20          [<ffffffff8150ca37>] unix_find_other+0x117/0x230

31                         unix_table_lock              4          [<ffffffff8150a09f>] unix_autobind+0x11f/0x1b0





This excerpt shows the first two lock class statistics. Line 01 shows the

output version - each time the format changes this will be updated. Line 02-04
@@ -131,9 +130,9 @@ The integer part of the time values is in us. 


Dealing with nested locks, subclasses may appear:



32...............................................................................................................................................................................................

32...........................................................................................................................................................................................................................

33

34                               &rq->lock:         13128          13128           0.43         190.53      103881.26          97454        3453404           0.00         401.11    13224683.11

34                               &rq->lock:       13128          13128           0.43         190.53      103881.26           7.91          97454        3453404           0.00         401.11    13224683.11           3.82

35                               ---------

36                               &rq->lock          645          [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75

37                               &rq->lock          297          [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
@@ -145,9 +144,9 @@ Dealing with nested locks, subclasses may appear: 
43                               &rq->lock         4715          [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54

44                               &rq->lock          893          [<ffffffff81340524>] schedule+0x157/0x7b8

45

46...............................................................................................................................................................................................

46...........................................................................................................................................................................................................................

47

48                             &rq->lock/1:         11526          11488           0.33         388.73      136294.31          21461          38404           0.00          37.93      109388.53

48                             &rq->lock/1:        1526          11488           0.33         388.73      136294.31          11.86          21461          38404           0.00          37.93      109388.53           2.84

49                             -----------

50                             &rq->lock/1        11526          [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54

51                             -----------
@@ -163,16 +162,16 @@ double_rq_lock actually acquires a nested lock of two spinlocks. 
View the top contending locks:



# grep : /proc/lock_stat | head

              &inode->i_data.tree_lock-W:            15          21657           0.18     1093295.30 11547131054.85             58          10415           0.16          87.51        6387.60

              &inode->i_data.tree_lock-R:             0              0           0.00           0.00           0.00          23302         231198           0.25           8.45       98023.38

                             dcache_lock:          1037           1161           0.38          45.32         774.51           6611         243371           0.15         306.48       77387.24

                         &inode->i_mutex:           161            286 18446744073709       62882.54     1244614.55           3653          20598 18446744073709       62318.60     1693822.74

                         &zone->lru_lock:            94             94           0.53           7.33          92.10           4366          32690           0.29          59.81       16350.06

              &inode->i_data.i_mmap_mutex:            79             79           0.40           3.77          53.03          11779          87755           0.28         116.93       29898.44

                        &q->__queue_lock:            48             50           0.52          31.62          86.31            774          13131           0.17         113.08       12277.52

                        &rq->rq_lock_key:            43             47           0.74          68.50         170.63           3706          33929           0.22         107.99       17460.62

                      &rq->rq_lock_key#2:            39             46           0.75           6.68          49.03           2979          32292           0.17         125.17       17137.63

                         tasklist_lock-W:            15             15           1.45          10.87          32.70           1201           7390           0.58          62.55       13648.47

			clockevents_lock:       2926159        2947636           0.15       46882.81  1784540466.34         605.41        3381345        3879161           0.00        2260.97    53178395.68          13.71

		     tick_broadcast_lock:        346460         346717           0.18        2257.43    39364622.71         113.54        3642919        4242696           0.00        2263.79    49173646.60          11.59

		  &mapping->i_mmap_mutex:        203896         203899           3.36      645530.05 31767507988.39      155800.21        3361776        8893984           0.17        2254.15    14110121.02           1.59

			       &rq->lock:        135014         136909           0.18         606.09      842160.68           6.15        1540728       10436146           0.00         728.72    17606683.41           1.69

	       &(&zone->lru_lock)->rlock:         93000          94934           0.16          59.18      188253.78           1.98        1199912        3809894           0.15         391.40     3559518.81           0.93

			 tasklist_lock-W:         40667          41130           0.23        1189.42      428980.51          10.43         270278         510106           0.16         653.51     3939674.91           7.72

			 tasklist_lock-R:         21298          21305           0.20        1310.05      215511.12          10.12         186204         241258           0.14        1162.33     1179779.23           4.89

			      rcu_node_1:         47656          49022           0.16         635.41      193616.41           3.95         844888        1865423           0.00         764.26     1656226.96           0.89

       &(&dentry->d_lockref.lock)->rlock:         39791          40179           0.15        1302.08       88851.96           2.21        2790851       12527025           0.10        1910.75     3379714.27           0.27

			      rcu_node_0:         29203          30064           0.16         786.55     1555573.00          51.74          88963         244254           0.00         398.87      428872.51           1.76



Clear the statistics:

Documentation/mutex-design.txt

+5 −5
Original line number Diff line number Diff line
@@ -116,11 +116,11 @@ using mutexes at the moment, please let me know if you find any. ] 
Implementation of mutexes

-------------------------



'struct mutex' is the new mutex type, defined in include/linux/mutex.h

and implemented in kernel/mutex.c. It is a counter-based mutex with a

spinlock and a wait-list. The counter has 3 states: 1 for "unlocked",

0 for "locked" and negative numbers (usually -1) for "locked, potential

waiters queued".

'struct mutex' is the new mutex type, defined in include/linux/mutex.h and

implemented in kernel/locking/mutex.c. It is a counter-based mutex with a

spinlock and a wait-list. The counter has 3 states: 1 for "unlocked", 0 for

"locked" and negative numbers (usually -1) for "locked, potential waiters

queued".



the APIs of 'struct mutex' have been streamlined:

arch/x86/Kconfig

+3 −3
Original line number Diff line number Diff line
@@ -635,10 +635,10 @@ config PARAVIRT_SPINLOCKS 
	  spinlock implementation with something virtualization-friendly

	  (for example, block the virtual CPU rather than spinning).



	  Unfortunately the downside is an up to 5% performance hit on

	  native kernels, with various workloads.

	  It has a minimal impact on native kernels and gives a nice performance

	  benefit on paravirtualized KVM / Xen kernels.



	  If you are unsure how to answer this question, answer N.

	  If you are unsure how to answer this question, answer Y.



source "arch/x86/xen/Kconfig"

arch/x86/kernel/alternative.c

+0 −11
Original line number Diff line number Diff line
@@ -402,17 +402,6 @@ void alternatives_enable_smp(void) 
{

	struct smp_alt_module *mod;



#ifdef CONFIG_LOCKDEP

	/*

	 * Older binutils section handling bug prevented

	 * alternatives-replacement from working reliably.

	 *

	 * If this still occurs then you should see a hang

	 * or crash shortly after this line:

	 */

	pr_info("lockdep: fixing up alternatives\n");

#endif



	/* Why bother if there are no other CPUs? */

	BUG_ON(num_possible_cpus() == 1);