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, 145 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/log-writes.rst b/Documentation/admin-guide/device-mapper/log-writes.rst
new file mode 100644
index 000000000..23141f2ff
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/log-writes.rst
@@ -0,0 +1,145 @@
+=============
+dm-log-writes
+=============
+
+This target takes 2 devices, one to pass all IO to normally, and one to log all
+of the write operations to.  This is intended for file system developers wishing
+to verify the integrity of metadata or data as the file system is written to.
+There is a log_write_entry written for every WRITE request and the target is
+able to take arbitrary data from userspace to insert into the log.  The data
+that is in the WRITE requests is copied into the log to make the replay happen
+exactly as it happened originally.
+
+Log Ordering
+============
+
+We log things in order of completion once we are sure the write is no longer in
+cache.  This means that normal WRITE requests are not actually logged until the
+next REQ_PREFLUSH request.  This is to make it easier for userspace to replay
+the log in a way that correlates to what is on disk and not what is in cache,
+to make it easier to detect improper waiting/flushing.
+
+This works by attaching all WRITE requests to a list once the write completes.
+Once we see a REQ_PREFLUSH request we splice this list onto the request and once
+the FLUSH request completes we log all of the WRITEs and then the FLUSH.  Only
+completed WRITEs, at the time the REQ_PREFLUSH is issued, are added in order to
+simulate the worst case scenario with regard to power failures.  Consider the
+following example (W means write, C means complete):
+
+	W1,W2,W3,C3,C2,Wflush,C1,Cflush
+
+The log would show the following:
+
+	W3,W2,flush,W1....
+
+Again this is to simulate what is actually on disk, this allows us to detect
+cases where a power failure at a particular point in time would create an
+inconsistent file system.
+
+Any REQ_FUA requests bypass this flushing mechanism and are logged as soon as
+they complete as those requests will obviously bypass the device cache.
+
+Any REQ_OP_DISCARD requests are treated like WRITE requests.  Otherwise we would
+have all the DISCARD requests, and then the WRITE requests and then the FLUSH
+request.  Consider the following example:
+
+	WRITE block 1, DISCARD block 1, FLUSH
+
+If we logged DISCARD when it completed, the replay would look like this:
+
+	DISCARD 1, WRITE 1, FLUSH
+
+which isn't quite what happened and wouldn't be caught during the log replay.
+
+Target interface
+================
+
+i) Constructor
+
+   log-writes <dev_path> <log_dev_path>
+
+   ============= ==============================================
+   dev_path	 Device that all of the IO will go to normally.
+   log_dev_path  Device where the log entries are written to.
+   ============= ==============================================
+
+ii) Status
+
+    <#logged entries> <highest allocated sector>
+
+    =========================== ========================
+    #logged entries	        Number of logged entries
+    highest allocated sector    Highest allocated sector
+    =========================== ========================
+
+iii) Messages
+
+    mark <description>
+
+	You can use a dmsetup message to set an arbitrary mark in a log.
+	For example say you want to fsck a file system after every
+	write, but first you need to replay up to the mkfs to make sure
+	we're fsck'ing something reasonable, you would do something like
+	this::
+
+	  mkfs.btrfs -f /dev/mapper/log
+	  dmsetup message log 0 mark mkfs
+	  <run test>
+
+	This would allow you to replay the log up to the mkfs mark and
+	then replay from that point on doing the fsck check in the
+	interval that you want.
+
+	Every log has a mark at the end labeled "dm-log-writes-end".
+
+Userspace component
+===================
+
+There is a userspace tool that will replay the log for you in various ways.
+It can be found here: https://github.com/josefbacik/log-writes
+
+Example usage
+=============
+
+Say you want to test fsync on your file system.  You would do something like
+this::
+
+  TABLE="0 $(blockdev --getsz /dev/sdb) log-writes /dev/sdb /dev/sdc"
+  dmsetup create log --table "$TABLE"
+  mkfs.btrfs -f /dev/mapper/log
+  dmsetup message log 0 mark mkfs
+
+  mount /dev/mapper/log /mnt/btrfs-test
+  <some test that does fsync at the end>
+  dmsetup message log 0 mark fsync
+  md5sum /mnt/btrfs-test/foo
+  umount /mnt/btrfs-test
+
+  dmsetup remove log
+  replay-log --log /dev/sdc --replay /dev/sdb --end-mark fsync
+  mount /dev/sdb /mnt/btrfs-test
+  md5sum /mnt/btrfs-test/foo
+  <verify md5sum's are correct>
+
+  Another option is to do a complicated file system operation and verify the file
+  system is consistent during the entire operation.  You could do this with:
+
+  TABLE="0 $(blockdev --getsz /dev/sdb) log-writes /dev/sdb /dev/sdc"
+  dmsetup create log --table "$TABLE"
+  mkfs.btrfs -f /dev/mapper/log
+  dmsetup message log 0 mark mkfs
+
+  mount /dev/mapper/log /mnt/btrfs-test
+  <fsstress to dirty the fs>
+  btrfs filesystem balance /mnt/btrfs-test
+  umount /mnt/btrfs-test
+  dmsetup remove log
+
+  replay-log --log /dev/sdc --replay /dev/sdb --end-mark mkfs
+  btrfsck /dev/sdb
+  replay-log --log /dev/sdc --replay /dev/sdb --start-mark mkfs \
+	--fsck "btrfsck /dev/sdb" --check fua
+
+And that will replay the log until it sees a FUA request, run the fsck command
+and if the fsck passes it will replay to the next FUA, until it is completed or
+the fsck command exists abnormally.