Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 337 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/cache.rst b/Documentation/admin-guide/device-mapper/cache.rst
new file mode 100644
index 000000000..f15e5254d
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/cache.rst
@@ -0,0 +1,337 @@
+=====
+Cache
+=====
+
+Introduction
+============
+
+dm-cache is a device mapper target written by Joe Thornber, Heinz
+Mauelshagen, and Mike Snitzer.
+
+It aims to improve performance of a block device (eg, a spindle) by
+dynamically migrating some of its data to a faster, smaller device
+(eg, an SSD).
+
+This device-mapper solution allows us to insert this caching at
+different levels of the dm stack, for instance above the data device for
+a thin-provisioning pool.  Caching solutions that are integrated more
+closely with the virtual memory system should give better performance.
+
+The target reuses the metadata library used in the thin-provisioning
+library.
+
+The decision as to what data to migrate and when is left to a plug-in
+policy module.  Several of these have been written as we experiment,
+and we hope other people will contribute others for specific io
+scenarios (eg. a vm image server).
+
+Glossary
+========
+
+  Migration
+	       Movement of the primary copy of a logical block from one
+	       device to the other.
+  Promotion
+	       Migration from slow device to fast device.
+  Demotion
+	       Migration from fast device to slow device.
+
+The origin device always contains a copy of the logical block, which
+may be out of date or kept in sync with the copy on the cache device
+(depending on policy).
+
+Design
+======
+
+Sub-devices
+-----------
+
+The target is constructed by passing three devices to it (along with
+other parameters detailed later):
+
+1. An origin device - the big, slow one.
+
+2. A cache device - the small, fast one.
+
+3. A small metadata device - records which blocks are in the cache,
+   which are dirty, and extra hints for use by the policy object.
+   This information could be put on the cache device, but having it
+   separate allows the volume manager to configure it differently,
+   e.g. as a mirror for extra robustness.  This metadata device may only
+   be used by a single cache device.
+
+Fixed block size
+----------------
+
+The origin is divided up into blocks of a fixed size.  This block size
+is configurable when you first create the cache.  Typically we've been
+using block sizes of 256KB - 1024KB.  The block size must be between 64
+sectors (32KB) and 2097152 sectors (1GB) and a multiple of 64 sectors (32KB).
+
+Having a fixed block size simplifies the target a lot.  But it is
+something of a compromise.  For instance, a small part of a block may be
+getting hit a lot, yet the whole block will be promoted to the cache.
+So large block sizes are bad because they waste cache space.  And small
+block sizes are bad because they increase the amount of metadata (both
+in core and on disk).
+
+Cache operating modes
+---------------------
+
+The cache has three operating modes: writeback, writethrough and
+passthrough.
+
+If writeback, the default, is selected then a write to a block that is
+cached will go only to the cache and the block will be marked dirty in
+the metadata.
+
+If writethrough is selected then a write to a cached block will not
+complete until it has hit both the origin and cache devices.  Clean
+blocks should remain clean.
+
+If passthrough is selected, useful when the cache contents are not known
+to be coherent with the origin device, then all reads are served from
+the origin device (all reads miss the cache) and all writes are
+forwarded to the origin device; additionally, write hits cause cache
+block invalidates.  To enable passthrough mode the cache must be clean.
+Passthrough mode allows a cache device to be activated without having to
+worry about coherency.  Coherency that exists is maintained, although
+the cache will gradually cool as writes take place.  If the coherency of
+the cache can later be verified, or established through use of the
+"invalidate_cblocks" message, the cache device can be transitioned to
+writethrough or writeback mode while still warm.  Otherwise, the cache
+contents can be discarded prior to transitioning to the desired
+operating mode.
+
+A simple cleaner policy is provided, which will clean (write back) all
+dirty blocks in a cache.  Useful for decommissioning a cache or when
+shrinking a cache.  Shrinking the cache's fast device requires all cache
+blocks, in the area of the cache being removed, to be clean.  If the
+area being removed from the cache still contains dirty blocks the resize
+will fail.  Care must be taken to never reduce the volume used for the
+cache's fast device until the cache is clean.  This is of particular
+importance if writeback mode is used.  Writethrough and passthrough
+modes already maintain a clean cache.  Future support to partially clean
+the cache, above a specified threshold, will allow for keeping the cache
+warm and in writeback mode during resize.
+
+Migration throttling
+--------------------
+
+Migrating data between the origin and cache device uses bandwidth.
+The user can set a throttle to prevent more than a certain amount of
+migration occurring at any one time.  Currently we're not taking any
+account of normal io traffic going to the devices.  More work needs
+doing here to avoid migrating during those peak io moments.
+
+For the time being, a message "migration_threshold <#sectors>"
+can be used to set the maximum number of sectors being migrated,
+the default being 2048 sectors (1MB).
+
+Updating on-disk metadata
+-------------------------
+
+On-disk metadata is committed every time a FLUSH or FUA bio is written.
+If no such requests are made then commits will occur every second.  This
+means the cache behaves like a physical disk that has a volatile write
+cache.  If power is lost you may lose some recent writes.  The metadata
+should always be consistent in spite of any crash.
+
+The 'dirty' state for a cache block changes far too frequently for us
+to keep updating it on the fly.  So we treat it as a hint.  In normal
+operation it will be written when the dm device is suspended.  If the
+system crashes all cache blocks will be assumed dirty when restarted.
+
+Per-block policy hints
+----------------------
+
+Policy plug-ins can store a chunk of data per cache block.  It's up to
+the policy how big this chunk is, but it should be kept small.  Like the
+dirty flags this data is lost if there's a crash so a safe fallback
+value should always be possible.
+
+Policy hints affect performance, not correctness.
+
+Policy messaging
+----------------
+
+Policies will have different tunables, specific to each one, so we
+need a generic way of getting and setting these.  Device-mapper
+messages are used.  Refer to cache-policies.txt.
+
+Discard bitset resolution
+-------------------------
+
+We can avoid copying data during migration if we know the block has
+been discarded.  A prime example of this is when mkfs discards the
+whole block device.  We store a bitset tracking the discard state of
+blocks.  However, we allow this bitset to have a different block size
+from the cache blocks.  This is because we need to track the discard
+state for all of the origin device (compare with the dirty bitset
+which is just for the smaller cache device).
+
+Target interface
+================
+
+Constructor
+-----------
+
+  ::
+
+   cache <metadata dev> <cache dev> <origin dev> <block size>
+         <#feature args> [<feature arg>]*
+         <policy> <#policy args> [policy args]*
+
+ ================ =======================================================
+ metadata dev     fast device holding the persistent metadata
+ cache dev	  fast device holding cached data blocks
+ origin dev	  slow device holding original data blocks
+ block size       cache unit size in sectors
+
+ #feature args    number of feature arguments passed
+ feature args     writethrough or passthrough (The default is writeback.)
+
+ policy           the replacement policy to use
+ #policy args     an even number of arguments corresponding to
+                  key/value pairs passed to the policy
+ policy args      key/value pairs passed to the policy
+		  E.g. 'sequential_threshold 1024'
+		  See cache-policies.txt for details.
+ ================ =======================================================
+
+Optional feature arguments are:
+
+
+   ==================== ========================================================
+   writethrough		write through caching that prohibits cache block
+			content from being different from origin block content.
+			Without this argument, the default behaviour is to write
+			back cache block contents later for performance reasons,
+			so they may differ from the corresponding origin blocks.
+
+   passthrough		a degraded mode useful for various cache coherency
+			situations (e.g., rolling back snapshots of
+			underlying storage).	 Reads and writes always go to
+			the origin.	If a write goes to a cached origin
+			block, then the cache block is invalidated.
+			To enable passthrough mode the cache must be clean.
+
+   metadata2		use version 2 of the metadata.  This stores the dirty
+			bits in a separate btree, which improves speed of
+			shutting down the cache.
+
+   no_discard_passdown	disable passing down discards from the cache
+			to the origin's data device.
+   ==================== ========================================================
+
+A policy called 'default' is always registered.  This is an alias for
+the policy we currently think is giving best all round performance.
+
+As the default policy could vary between kernels, if you are relying on
+the characteristics of a specific policy, always request it by name.
+
+Status
+------
+
+::
+
+  <metadata block size> <#used metadata blocks>/<#total metadata blocks>
+  <cache block size> <#used cache blocks>/<#total cache blocks>
+  <#read hits> <#read misses> <#write hits> <#write misses>
+  <#demotions> <#promotions> <#dirty> <#features> <features>*
+  <#core args> <core args>* <policy name> <#policy args> <policy args>*
+  <cache metadata mode>
+
+
+========================= =====================================================
+metadata block size	  Fixed block size for each metadata block in
+			  sectors
+#used metadata blocks	  Number of metadata blocks used
+#total metadata blocks	  Total number of metadata blocks
+cache block size	  Configurable block size for the cache device
+			  in sectors
+#used cache blocks	  Number of blocks resident in the cache
+#total cache blocks	  Total number of cache blocks
+#read hits		  Number of times a READ bio has been mapped
+			  to the cache
+#read misses		  Number of times a READ bio has been mapped
+			  to the origin
+#write hits		  Number of times a WRITE bio has been mapped
+			  to the cache
+#write misses		  Number of times a WRITE bio has been
+			  mapped to the origin
+#demotions		  Number of times a block has been removed
+			  from the cache
+#promotions		  Number of times a block has been moved to
+			  the cache
+#dirty			  Number of blocks in the cache that differ
+			  from the origin
+#feature args		  Number of feature args to follow
+feature args		  'writethrough' (optional)
+#core args		  Number of core arguments (must be even)
+core args		  Key/value pairs for tuning the core
+			  e.g. migration_threshold
+policy name		  Name of the policy
+#policy args		  Number of policy arguments to follow (must be even)
+policy args		  Key/value pairs e.g. sequential_threshold
+cache metadata mode       ro if read-only, rw if read-write
+
+			  In serious cases where even a read-only mode is
+			  deemed unsafe no further I/O will be permitted and
+			  the status will just contain the string 'Fail'.
+			  The userspace recovery tools should then be used.
+needs_check		  'needs_check' if set, '-' if not set
+			  A metadata operation has failed, resulting in the
+			  needs_check flag being set in the metadata's
+			  superblock.  The metadata device must be
+			  deactivated and checked/repaired before the
+			  cache can be made fully operational again.
+			  '-' indicates	needs_check is not set.
+========================= =====================================================
+
+Messages
+--------
+
+Policies will have different tunables, specific to each one, so we
+need a generic way of getting and setting these.  Device-mapper
+messages are used.  (A sysfs interface would also be possible.)
+
+The message format is::
+
+   <key> <value>
+
+E.g.::
+
+   dmsetup message my_cache 0 sequential_threshold 1024
+
+
+Invalidation is removing an entry from the cache without writing it
+back.  Cache blocks can be invalidated via the invalidate_cblocks
+message, which takes an arbitrary number of cblock ranges.  Each cblock
+range's end value is "one past the end", meaning 5-10 expresses a range
+of values from 5 to 9.  Each cblock must be expressed as a decimal
+value, in the future a variant message that takes cblock ranges
+expressed in hexadecimal may be needed to better support efficient
+invalidation of larger caches.  The cache must be in passthrough mode
+when invalidate_cblocks is used::
+
+   invalidate_cblocks [<cblock>|<cblock begin>-<cblock end>]*
+
+E.g.::
+
+   dmsetup message my_cache 0 invalidate_cblocks 2345 3456-4567 5678-6789
+
+Examples
+========
+
+The test suite can be found here:
+
+https://github.com/jthornber/device-mapper-test-suite
+
+::
+
+  dmsetup create my_cache --table '0 41943040 cache /dev/mapper/metadata \
+	  /dev/mapper/ssd /dev/mapper/origin 512 1 writeback default 0'
+  dmsetup create my_cache --table '0 41943040 cache /dev/mapper/metadata \
+	  /dev/mapper/ssd /dev/mapper/origin 1024 1 writeback \
+	  mq 4 sequential_threshold 1024 random_threshold 8'