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, 153 insertions, 0 deletions

diff --git a/Documentation/admin-guide/blockdev/ramdisk.rst b/Documentation/admin-guide/blockdev/ramdisk.rst
new file mode 100644
index 000000000..9ce6101e8
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/ramdisk.rst
@@ -0,0 +1,153 @@
+==========================================
+Using the RAM disk block device with Linux
+==========================================
+
+.. Contents:
+
+	1) Overview
+	2) Kernel Command Line Parameters
+	3) Using "rdev"
+	4) An Example of Creating a Compressed RAM Disk
+
+
+1) Overview
+-----------
+
+The RAM disk driver is a way to use main system memory as a block device.  It
+is required for initrd, an initial filesystem used if you need to load modules
+in order to access the root filesystem (see Documentation/admin-guide/initrd.rst).  It can
+also be used for a temporary filesystem for crypto work, since the contents
+are erased on reboot.
+
+The RAM disk dynamically grows as more space is required. It does this by using
+RAM from the buffer cache. The driver marks the buffers it is using as dirty
+so that the VM subsystem does not try to reclaim them later.
+
+The RAM disk supports up to 16 RAM disks by default, and can be reconfigured
+to support an unlimited number of RAM disks (at your own risk).  Just change
+the configuration symbol BLK_DEV_RAM_COUNT in the Block drivers config menu
+and (re)build the kernel.
+
+To use RAM disk support with your system, run './MAKEDEV ram' from the /dev
+directory.  RAM disks are all major number 1, and start with minor number 0
+for /dev/ram0, etc.  If used, modern kernels use /dev/ram0 for an initrd.
+
+The new RAM disk also has the ability to load compressed RAM disk images,
+allowing one to squeeze more programs onto an average installation or
+rescue floppy disk.
+
+
+2) Parameters
+---------------------------------
+
+2a) Kernel Command Line Parameters
+
+	ramdisk_size=N
+		Size of the ramdisk.
+
+This parameter tells the RAM disk driver to set up RAM disks of N k size.  The
+default is 4096 (4 MB).
+
+2b) Module parameters
+
+	rd_nr
+		/dev/ramX devices created.
+
+	max_part
+		Maximum partition number.
+
+	rd_size
+		See ramdisk_size.
+
+3) Using "rdev"
+---------------
+
+"rdev" is an obsolete, deprecated, antiquated utility that could be used
+to set the boot device in a Linux kernel image.
+
+Instead of using rdev, just place the boot device information on the
+kernel command line and pass it to the kernel from the bootloader.
+
+You can also pass arguments to the kernel by setting FDARGS in
+arch/x86/boot/Makefile and specify in initrd image by setting FDINITRD in
+arch/x86/boot/Makefile.
+
+Some of the kernel command line boot options that may apply here are::
+
+  ramdisk_start=N
+  ramdisk_size=M
+
+If you make a boot disk that has LILO, then for the above, you would use::
+
+	append = "ramdisk_start=N ramdisk_size=M"
+
+4) An Example of Creating a Compressed RAM Disk
+-----------------------------------------------
+
+To create a RAM disk image, you will need a spare block device to
+construct it on. This can be the RAM disk device itself, or an
+unused disk partition (such as an unmounted swap partition). For this
+example, we will use the RAM disk device, "/dev/ram0".
+
+Note: This technique should not be done on a machine with less than 8 MB
+of RAM. If using a spare disk partition instead of /dev/ram0, then this
+restriction does not apply.
+
+a) Decide on the RAM disk size that you want. Say 2 MB for this example.
+   Create it by writing to the RAM disk device. (This step is not currently
+   required, but may be in the future.) It is wise to zero out the
+   area (esp. for disks) so that maximal compression is achieved for
+   the unused blocks of the image that you are about to create::
+
+	dd if=/dev/zero of=/dev/ram0 bs=1k count=2048
+
+b) Make a filesystem on it. Say ext2fs for this example::
+
+	mke2fs -vm0 /dev/ram0 2048
+
+c) Mount it, copy the files you want to it (eg: /etc/* /dev/* ...)
+   and unmount it again.
+
+d) Compress the contents of the RAM disk. The level of compression
+   will be approximately 50% of the space used by the files. Unused
+   space on the RAM disk will compress to almost nothing::
+
+	dd if=/dev/ram0 bs=1k count=2048 | gzip -v9 > /tmp/ram_image.gz
+
+e) Put the kernel onto the floppy::
+
+	dd if=zImage of=/dev/fd0 bs=1k
+
+f) Put the RAM disk image onto the floppy, after the kernel. Use an offset
+   that is slightly larger than the kernel, so that you can put another
+   (possibly larger) kernel onto the same floppy later without overlapping
+   the RAM disk image. An offset of 400 kB for kernels about 350 kB in
+   size would be reasonable. Make sure offset+size of ram_image.gz is
+   not larger than the total space on your floppy (usually 1440 kB)::
+
+	dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400
+
+g) Make sure that you have already specified the boot information in
+   FDARGS and FDINITRD or that you use a bootloader to pass kernel
+   command line boot options to the kernel.
+
+That is it. You now have your boot/root compressed RAM disk floppy. Some
+users may wish to combine steps (d) and (f) by using a pipe.
+
+
+						Paul Gortmaker 12/95
+
+Changelog:
+----------
+
+SEPT-2020 :
+
+                Removed usage of "rdev"
+
+10-22-04 :
+		Updated to reflect changes in command line options, remove
+		obsolete references, general cleanup.
+		James Nelson (james4765@gmail.com)
+
+12-95 :
+		Original Document