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, 383 insertions, 0 deletions

diff --git a/Documentation/admin-guide/initrd.rst b/Documentation/admin-guide/initrd.rst
new file mode 100644
index 000000000..6c1660a4c
--- /dev/null
+++ b/Documentation/admin-guide/initrd.rst
@@ -0,0 +1,383 @@
+Using the initial RAM disk (initrd)
+===================================
+
+Written 1996,2000 by Werner Almesberger <werner.almesberger@epfl.ch> and
+Hans Lermen <lermen@fgan.de>
+
+
+initrd provides the capability to load a RAM disk by the boot loader.
+This RAM disk can then be mounted as the root file system and programs
+can be run from it. Afterwards, a new root file system can be mounted
+from a different device. The previous root (from initrd) is then moved
+to a directory and can be subsequently unmounted.
+
+initrd is mainly designed to allow system startup to occur in two phases,
+where the kernel comes up with a minimum set of compiled-in drivers, and
+where additional modules are loaded from initrd.
+
+This document gives a brief overview of the use of initrd. A more detailed
+discussion of the boot process can be found in [#f1]_.
+
+
+Operation
+---------
+
+When using initrd, the system typically boots as follows:
+
+  1) the boot loader loads the kernel and the initial RAM disk
+  2) the kernel converts initrd into a "normal" RAM disk and
+     frees the memory used by initrd
+  3) if the root device is not ``/dev/ram0``, the old (deprecated)
+     change_root procedure is followed. see the "Obsolete root change
+     mechanism" section below.
+  4) root device is mounted. if it is ``/dev/ram0``, the initrd image is
+     then mounted as root
+  5) /sbin/init is executed (this can be any valid executable, including
+     shell scripts; it is run with uid 0 and can do basically everything
+     init can do).
+  6) init mounts the "real" root file system
+  7) init places the root file system at the root directory using the
+     pivot_root system call
+  8) init execs the ``/sbin/init`` on the new root filesystem, performing
+     the usual boot sequence
+  9) the initrd file system is removed
+
+Note that changing the root directory does not involve unmounting it.
+It is therefore possible to leave processes running on initrd during that
+procedure. Also note that file systems mounted under initrd continue to
+be accessible.
+
+
+Boot command-line options
+-------------------------
+
+initrd adds the following new options::
+
+  initrd=<path>    (e.g. LOADLIN)
+
+    Loads the specified file as the initial RAM disk. When using LILO, you
+    have to specify the RAM disk image file in /etc/lilo.conf, using the
+    INITRD configuration variable.
+
+  noinitrd
+
+    initrd data is preserved but it is not converted to a RAM disk and
+    the "normal" root file system is mounted. initrd data can be read
+    from /dev/initrd. Note that the data in initrd can have any structure
+    in this case and doesn't necessarily have to be a file system image.
+    This option is used mainly for debugging.
+
+    Note: /dev/initrd is read-only and it can only be used once. As soon
+    as the last process has closed it, all data is freed and /dev/initrd
+    can't be opened anymore.
+
+  root=/dev/ram0
+
+    initrd is mounted as root, and the normal boot procedure is followed,
+    with the RAM disk mounted as root.
+
+Compressed cpio images
+----------------------
+
+Recent kernels have support for populating a ramdisk from a compressed cpio
+archive. On such systems, the creation of a ramdisk image doesn't need to
+involve special block devices or loopbacks; you merely create a directory on
+disk with the desired initrd content, cd to that directory, and run (as an
+example)::
+
+	find . | cpio --quiet -H newc -o | gzip -9 -n > /boot/imagefile.img
+
+Examining the contents of an existing image file is just as simple::
+
+	mkdir /tmp/imagefile
+	cd /tmp/imagefile
+	gzip -cd /boot/imagefile.img | cpio -imd --quiet
+
+Installation
+------------
+
+First, a directory for the initrd file system has to be created on the
+"normal" root file system, e.g.::
+
+	# mkdir /initrd
+
+The name is not relevant. More details can be found on the
+:manpage:`pivot_root(2)` man page.
+
+If the root file system is created during the boot procedure (i.e. if
+you're building an install floppy), the root file system creation
+procedure should create the ``/initrd`` directory.
+
+If initrd will not be mounted in some cases, its content is still
+accessible if the following device has been created::
+
+	# mknod /dev/initrd b 1 250
+	# chmod 400 /dev/initrd
+
+Second, the kernel has to be compiled with RAM disk support and with
+support for the initial RAM disk enabled. Also, at least all components
+needed to execute programs from initrd (e.g. executable format and file
+system) must be compiled into the kernel.
+
+Third, you have to create the RAM disk image. This is done by creating a
+file system on a block device, copying files to it as needed, and then
+copying the content of the block device to the initrd file. With recent
+kernels, at least three types of devices are suitable for that:
+
+ - a floppy disk (works everywhere but it's painfully slow)
+ - a RAM disk (fast, but allocates physical memory)
+ - a loopback device (the most elegant solution)
+
+We'll describe the loopback device method:
+
+ 1) make sure loopback block devices are configured into the kernel
+ 2) create an empty file system of the appropriate size, e.g.::
+
+	# dd if=/dev/zero of=initrd bs=300k count=1
+	# mke2fs -F -m0 initrd
+
+    (if space is critical, you may want to use the Minix FS instead of Ext2)
+ 3) mount the file system, e.g.::
+
+	# mount -t ext2 -o loop initrd /mnt
+
+ 4) create the console device::
+
+    # mkdir /mnt/dev
+    # mknod /mnt/dev/console c 5 1
+
+ 5) copy all the files that are needed to properly use the initrd
+    environment. Don't forget the most important file, ``/sbin/init``
+
+    .. note:: ``/sbin/init`` permissions must include "x" (execute).
+
+ 6) correct operation the initrd environment can frequently be tested
+    even without rebooting with the command::
+
+	# chroot /mnt /sbin/init
+
+    This is of course limited to initrds that do not interfere with the
+    general system state (e.g. by reconfiguring network interfaces,
+    overwriting mounted devices, trying to start already running demons,
+    etc. Note however that it is usually possible to use pivot_root in
+    such a chroot'ed initrd environment.)
+ 7) unmount the file system::
+
+	# umount /mnt
+
+ 8) the initrd is now in the file "initrd". Optionally, it can now be
+    compressed::
+
+	# gzip -9 initrd
+
+For experimenting with initrd, you may want to take a rescue floppy and
+only add a symbolic link from ``/sbin/init`` to ``/bin/sh``. Alternatively, you
+can try the experimental newlib environment [#f2]_ to create a small
+initrd.
+
+Finally, you have to boot the kernel and load initrd. Almost all Linux
+boot loaders support initrd. Since the boot process is still compatible
+with an older mechanism, the following boot command line parameters
+have to be given::
+
+  root=/dev/ram0 rw
+
+(rw is only necessary if writing to the initrd file system.)
+
+With LOADLIN, you simply execute::
+
+     LOADLIN <kernel> initrd=<disk_image>
+
+e.g.::
+
+	LOADLIN C:\LINUX\BZIMAGE initrd=C:\LINUX\INITRD.GZ root=/dev/ram0 rw
+
+With LILO, you add the option ``INITRD=<path>`` to either the global section
+or to the section of the respective kernel in ``/etc/lilo.conf``, and pass
+the options using APPEND, e.g.::
+
+  image = /bzImage
+    initrd = /boot/initrd.gz
+    append = "root=/dev/ram0 rw"
+
+and run ``/sbin/lilo``
+
+For other boot loaders, please refer to the respective documentation.
+
+Now you can boot and enjoy using initrd.
+
+
+Changing the root device
+------------------------
+
+When finished with its duties, init typically changes the root device
+and proceeds with starting the Linux system on the "real" root device.
+
+The procedure involves the following steps:
+ - mounting the new root file system
+ - turning it into the root file system
+ - removing all accesses to the old (initrd) root file system
+ - unmounting the initrd file system and de-allocating the RAM disk
+
+Mounting the new root file system is easy: it just needs to be mounted on
+a directory under the current root. Example::
+
+	# mkdir /new-root
+	# mount -o ro /dev/hda1 /new-root
+
+The root change is accomplished with the pivot_root system call, which
+is also available via the ``pivot_root`` utility (see :manpage:`pivot_root(8)`
+man page; ``pivot_root`` is distributed with util-linux version 2.10h or higher
+[#f3]_). ``pivot_root`` moves the current root to a directory under the new
+root, and puts the new root at its place. The directory for the old root
+must exist before calling ``pivot_root``. Example::
+
+	# cd /new-root
+	# mkdir initrd
+	# pivot_root . initrd
+
+Now, the init process may still access the old root via its
+executable, shared libraries, standard input/output/error, and its
+current root directory. All these references are dropped by the
+following command::
+
+	# exec chroot . what-follows <dev/console >dev/console 2>&1
+
+Where what-follows is a program under the new root, e.g. ``/sbin/init``
+If the new root file system will be used with udev and has no valid
+``/dev`` directory, udev must be initialized before invoking chroot in order
+to provide ``/dev/console``.
+
+Note: implementation details of pivot_root may change with time. In order
+to ensure compatibility, the following points should be observed:
+
+ - before calling pivot_root, the current directory of the invoking
+   process should point to the new root directory
+ - use . as the first argument, and the _relative_ path of the directory
+   for the old root as the second argument
+ - a chroot program must be available under the old and the new root
+ - chroot to the new root afterwards
+ - use relative paths for dev/console in the exec command
+
+Now, the initrd can be unmounted and the memory allocated by the RAM
+disk can be freed::
+
+	# umount /initrd
+	# blockdev --flushbufs /dev/ram0
+
+It is also possible to use initrd with an NFS-mounted root, see the
+:manpage:`pivot_root(8)` man page for details.
+
+
+Usage scenarios
+---------------
+
+The main motivation for implementing initrd was to allow for modular
+kernel configuration at system installation. The procedure would work
+as follows:
+
+  1) system boots from floppy or other media with a minimal kernel
+     (e.g. support for RAM disks, initrd, a.out, and the Ext2 FS) and
+     loads initrd
+  2) ``/sbin/init`` determines what is needed to (1) mount the "real" root FS
+     (i.e. device type, device drivers, file system) and (2) the
+     distribution media (e.g. CD-ROM, network, tape, ...). This can be
+     done by asking the user, by auto-probing, or by using a hybrid
+     approach.
+  3) ``/sbin/init`` loads the necessary kernel modules
+  4) ``/sbin/init`` creates and populates the root file system (this doesn't
+     have to be a very usable system yet)
+  5) ``/sbin/init`` invokes ``pivot_root`` to change the root file system and
+     execs - via chroot - a program that continues the installation
+  6) the boot loader is installed
+  7) the boot loader is configured to load an initrd with the set of
+     modules that was used to bring up the system (e.g. ``/initrd`` can be
+     modified, then unmounted, and finally, the image is written from
+     ``/dev/ram0`` or ``/dev/rd/0`` to a file)
+  8) now the system is bootable and additional installation tasks can be
+     performed
+
+The key role of initrd here is to reuse the configuration data during
+normal system operation without requiring the use of a bloated "generic"
+kernel or re-compiling or re-linking the kernel.
+
+A second scenario is for installations where Linux runs on systems with
+different hardware configurations in a single administrative domain. In
+such cases, it is desirable to generate only a small set of kernels
+(ideally only one) and to keep the system-specific part of configuration
+information as small as possible. In this case, a common initrd could be
+generated with all the necessary modules. Then, only ``/sbin/init`` or a file
+read by it would have to be different.
+
+A third scenario is more convenient recovery disks, because information
+like the location of the root FS partition doesn't have to be provided at
+boot time, but the system loaded from initrd can invoke a user-friendly
+dialog and it can also perform some sanity checks (or even some form of
+auto-detection).
+
+Last not least, CD-ROM distributors may use it for better installation
+from CD, e.g. by using a boot floppy and bootstrapping a bigger RAM disk
+via initrd from CD; or by booting via a loader like ``LOADLIN`` or directly
+from the CD-ROM, and loading the RAM disk from CD without need of
+floppies.
+
+
+Obsolete root change mechanism
+------------------------------
+
+The following mechanism was used before the introduction of pivot_root.
+Current kernels still support it, but you should _not_ rely on its
+continued availability.
+
+It works by mounting the "real" root device (i.e. the one set with rdev
+in the kernel image or with root=... at the boot command line) as the
+root file system when linuxrc exits. The initrd file system is then
+unmounted, or, if it is still busy, moved to a directory ``/initrd``, if
+such a directory exists on the new root file system.
+
+In order to use this mechanism, you do not have to specify the boot
+command options root, init, or rw. (If specified, they will affect
+the real root file system, not the initrd environment.)
+
+If /proc is mounted, the "real" root device can be changed from within
+linuxrc by writing the number of the new root FS device to the special
+file /proc/sys/kernel/real-root-dev, e.g.::
+
+  # echo 0x301 >/proc/sys/kernel/real-root-dev
+
+Note that the mechanism is incompatible with NFS and similar file
+systems.
+
+This old, deprecated mechanism is commonly called ``change_root``, while
+the new, supported mechanism is called ``pivot_root``.
+
+
+Mixed change_root and pivot_root mechanism
+------------------------------------------
+
+In case you did not want to use ``root=/dev/ram0`` to trigger the pivot_root
+mechanism, you may create both ``/linuxrc`` and ``/sbin/init`` in your initrd
+image.
+
+``/linuxrc`` would contain only the following::
+
+	#! /bin/sh
+	mount -n -t proc proc /proc
+	echo 0x0100 >/proc/sys/kernel/real-root-dev
+	umount -n /proc
+
+Once linuxrc exited, the kernel would mount again your initrd as root,
+this time executing ``/sbin/init``. Again, it would be the duty of this init
+to build the right environment (maybe using the ``root= device`` passed on
+the cmdline) before the final execution of the real ``/sbin/init``.
+
+
+Resources
+---------
+
+.. [#f1] Almesberger, Werner; "Booting Linux: The History and the Future"
+    https://www.almesberger.net/cv/papers/ols2k-9.ps.gz
+.. [#f2] newlib package (experimental), with initrd example
+    https://www.sourceware.org/newlib/
+.. [#f3] util-linux: Miscellaneous utilities for Linux
+    https://www.kernel.org/pub/linux/utils/util-linux/