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, 191 insertions, 0 deletions

diff --git a/Documentation/filesystems/ext4/attributes.rst b/Documentation/filesystems/ext4/attributes.rst
new file mode 100644
index 000000000..87814696a
--- /dev/null
+++ b/Documentation/filesystems/ext4/attributes.rst
@@ -0,0 +1,191 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Extended Attributes
+-------------------
+
+Extended attributes (xattrs) are typically stored in a separate data
+block on the disk and referenced from inodes via ``inode.i_file_acl*``.
+The first use of extended attributes seems to have been for storing file
+ACLs and other security data (selinux). With the ``user_xattr`` mount
+option it is possible for users to store extended attributes so long as
+all attribute names begin with “user”; this restriction seems to have
+disappeared as of Linux 3.0.
+
+There are two places where extended attributes can be found. The first
+place is between the end of each inode entry and the beginning of the
+next inode entry. For example, if inode.i_extra_isize = 28 and
+sb.inode_size = 256, then there are 256 - (128 + 28) = 100 bytes
+available for in-inode extended attribute storage. The second place
+where extended attributes can be found is in the block pointed to by
+``inode.i_file_acl``. As of Linux 3.11, it is not possible for this
+block to contain a pointer to a second extended attribute block (or even
+the remaining blocks of a cluster). In theory it is possible for each
+attribute's value to be stored in a separate data block, though as of
+Linux 3.11 the code does not permit this.
+
+Keys are generally assumed to be ASCIIZ strings, whereas values can be
+strings or binary data.
+
+Extended attributes, when stored after the inode, have a header
+``ext4_xattr_ibody_header`` that is 4 bytes long:
+
+.. list-table::
+   :widths: 8 8 24 40
+   :header-rows: 1
+
+   * - Offset
+     - Type
+     - Name
+     - Description
+   * - 0x0
+     - __le32
+     - h_magic
+     - Magic number for identification, 0xEA020000. This value is set by the
+       Linux driver, though e2fsprogs doesn't seem to check it(?)
+
+The beginning of an extended attribute block is in
+``struct ext4_xattr_header``, which is 32 bytes long:
+
+.. list-table::
+   :widths: 8 8 24 40
+   :header-rows: 1
+
+   * - Offset
+     - Type
+     - Name
+     - Description
+   * - 0x0
+     - __le32
+     - h_magic
+     - Magic number for identification, 0xEA020000.
+   * - 0x4
+     - __le32
+     - h_refcount
+     - Reference count.
+   * - 0x8
+     - __le32
+     - h_blocks
+     - Number of disk blocks used.
+   * - 0xC
+     - __le32
+     - h_hash
+     - Hash value of all attributes.
+   * - 0x10
+     - __le32
+     - h_checksum
+     - Checksum of the extended attribute block.
+   * - 0x14
+     - __u32
+     - h_reserved[3]
+     - Zero.
+
+The checksum is calculated against the FS UUID, the 64-bit block number
+of the extended attribute block, and the entire block (header +
+entries).
+
+Following the ``struct ext4_xattr_header`` or
+``struct ext4_xattr_ibody_header`` is an array of
+``struct ext4_xattr_entry``; each of these entries is at least 16 bytes
+long. When stored in an external block, the ``struct ext4_xattr_entry``
+entries must be stored in sorted order. The sort order is
+``e_name_index``, then ``e_name_len``, and finally ``e_name``.
+Attributes stored inside an inode do not need be stored in sorted order.
+
+.. list-table::
+   :widths: 8 8 24 40
+   :header-rows: 1
+
+   * - Offset
+     - Type
+     - Name
+     - Description
+   * - 0x0
+     - __u8
+     - e_name_len
+     - Length of name.
+   * - 0x1
+     - __u8
+     - e_name_index
+     - Attribute name index. There is a discussion of this below.
+   * - 0x2
+     - __le16
+     - e_value_offs
+     - Location of this attribute's value on the disk block where it is stored.
+       Multiple attributes can share the same value. For an inode attribute
+       this value is relative to the start of the first entry; for a block this
+       value is relative to the start of the block (i.e. the header).
+   * - 0x4
+     - __le32
+     - e_value_inum
+     - The inode where the value is stored. Zero indicates the value is in the
+       same block as this entry. This field is only used if the
+       INCOMPAT_EA_INODE feature is enabled.
+   * - 0x8
+     - __le32
+     - e_value_size
+     - Length of attribute value.
+   * - 0xC
+     - __le32
+     - e_hash
+     - Hash value of attribute name and attribute value. The kernel doesn't
+       update the hash for in-inode attributes, so for that case this value
+       must be zero, because e2fsck validates any non-zero hash regardless of
+       where the xattr lives.
+   * - 0x10
+     - char
+     - e_name[e_name_len]
+     - Attribute name. Does not include trailing NULL.
+
+Attribute values can follow the end of the entry table. There appears to
+be a requirement that they be aligned to 4-byte boundaries. The values
+are stored starting at the end of the block and grow towards the
+xattr_header/xattr_entry table. When the two collide, the overflow is
+put into a separate disk block. If the disk block fills up, the
+filesystem returns -ENOSPC.
+
+The first four fields of the ``ext4_xattr_entry`` are set to zero to
+mark the end of the key list.
+
+Attribute Name Indices
+~~~~~~~~~~~~~~~~~~~~~~
+
+Logically speaking, extended attributes are a series of key=value pairs.
+The keys are assumed to be NULL-terminated strings. To reduce the amount
+of on-disk space that the keys consume, the beginning of the key string
+is matched against the attribute name index. If a match is found, the
+attribute name index field is set, and matching string is removed from
+the key name. Here is a map of name index values to key prefixes:
+
+.. list-table::
+   :widths: 16 64
+   :header-rows: 1
+
+   * - Name Index
+     - Key Prefix
+   * - 0
+     - (no prefix)
+   * - 1
+     - “user.”
+   * - 2
+     - “system.posix_acl_access”
+   * - 3
+     - “system.posix_acl_default”
+   * - 4
+     - “trusted.”
+   * - 6
+     - “security.”
+   * - 7
+     - “system.” (inline_data only?)
+   * - 8
+     - “system.richacl” (SuSE kernels only?)
+
+For example, if the attribute key is “user.fubar”, the attribute name
+index is set to 1 and the “fubar” name is recorded on disk.
+
+POSIX ACLs
+~~~~~~~~~~
+
+POSIX ACLs are stored in a reduced version of the Linux kernel (and
+libacl's) internal ACL format. The key difference is that the version
+number is different (1) and the ``e_id`` field is only stored for named
+user and group ACLs.