Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 204 insertions, 0 deletions

diff --git a/Documentation/locking/lockstat.rst b/Documentation/locking/lockstat.rst
new file mode 100644
index 000000000..536eab8db
--- /dev/null
+++ b/Documentation/locking/lockstat.rst
@@ -0,0 +1,204 @@
+===============
+Lock Statistics
+===============
+
+What
+====
+
+As the name suggests, it provides statistics on locks.
+
+
+Why
+===
+
+Because things like lock contention can severely impact performance.
+
+How
+===
+
+Lockdep already has hooks in the lock functions and maps lock instances to
+lock classes. We build on that (see Documentation/locking/lockdep-design.rst).
+The graph below shows the relation between the lock functions and the various
+hooks therein::
+
+        __acquire
+            |
+           lock _____
+            |        \
+            |    __contended
+            |         |
+            |       <wait>
+            | _______/
+            |/
+            |
+       __acquired
+            |
+            .
+          <hold>
+            .
+            |
+       __release
+            |
+         unlock
+
+  lock, unlock	- the regular lock functions
+  __*		- the hooks
+  <> 		- states
+
+With these hooks we provide the following statistics:
+
+ con-bounces
+	- number of lock contention that involved x-cpu data
+ contentions
+	- number of lock acquisitions that had to wait
+ 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
+     avg
+	- average time this lock was held
+
+These numbers are gathered per lock class, per read/write state (when
+applicable).
+
+It also tracks 4 contention points per class. A contention point is a call site
+that had to wait on lock acquisition.
+
+Configuration
+-------------
+
+Lock statistics are enabled via CONFIG_LOCK_STAT.
+
+Usage
+-----
+
+Enable collection of statistics::
+
+	# echo 1 >/proc/sys/kernel/lock_stat
+
+Disable collection of statistics::
+
+	# echo 0 >/proc/sys/kernel/lock_stat
+
+Look at the current lock statistics::
+
+  ( line numbers not part of actual output, done for clarity in the explanation
+    below )
+
+  # less /proc/lock_stat
+
+  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:            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              1          [<ffffffff811502a7>] khugepaged_scan_mm_slot+0x57/0x280
+  10                           &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              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.............................................................................................................................................................................................................................
+  20
+  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
+show the header with column descriptions. Lines 05-18 and 20-31 show the actual
+statistics. These statistics come in two parts; the actual stats separated by a
+short separator (line 08, 13) from the contention points.
+
+Lines 09-12 show the first 4 recorded contention points (the code
+which tries to get the lock) and lines 14-17 show the first 4 recorded
+contended points (the lock holder). It is possible that the max
+con-bounces point is missing in the statistics.
+
+The first lock (05-18) is a read/write lock, and shows two lines above the
+short separator. The contention points don't match the column descriptors,
+they have two: contentions and [<IP>] symbol. The second set of contention
+points are the points we're contending with.
+
+The integer part of the time values is in us.
+
+Dealing with nested locks, subclasses may appear::
+
+  32...........................................................................................................................................................................................................................
+  33
+  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
+  38                               &rq->lock          360          [<ffffffff8103c4c5>] select_task_rq_fair+0x1f0/0x74a
+  39                               &rq->lock          428          [<ffffffff81045f98>] scheduler_tick+0x46/0x1fb
+  40                               ---------
+  41                               &rq->lock           77          [<ffffffff8103bfc4>] task_rq_lock+0x43/0x75
+  42                               &rq->lock          174          [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
+  43                               &rq->lock         4715          [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
+  44                               &rq->lock          893          [<ffffffff81340524>] schedule+0x157/0x7b8
+  45
+  46...........................................................................................................................................................................................................................
+  47
+  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                             -----------
+  52                             &rq->lock/1         5645          [<ffffffff8103ed4b>] double_rq_lock+0x42/0x54
+  53                             &rq->lock/1         1224          [<ffffffff81340524>] schedule+0x157/0x7b8
+  54                             &rq->lock/1         4336          [<ffffffff8103ed58>] double_rq_lock+0x4f/0x54
+  55                             &rq->lock/1          181          [<ffffffff8104ba65>] try_to_wake_up+0x127/0x25a
+
+Line 48 shows statistics for the second subclass (/1) of &rq->lock class
+(subclass starts from 0), since in this case, as line 50 suggests,
+double_rq_lock actually acquires a nested lock of two spinlocks.
+
+View the top contending locks::
+
+  # grep : /proc/lock_stat | head
+			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::
+
+  # echo 0 > /proc/lock_stat