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, 171 insertions, 0 deletions

diff --git a/Documentation/userspace-api/gpio/sysfs.rst b/Documentation/userspace-api/gpio/sysfs.rst
new file mode 100644
index 000000000..bd64896de
--- /dev/null
+++ b/Documentation/userspace-api/gpio/sysfs.rst
@@ -0,0 +1,171 @@
+GPIO Sysfs Interface for Userspace
+==================================
+
+.. warning::
+   This API is obsoleted by the chardev.rst and the ABI documentation has
+   been moved to Documentation/ABI/obsolete/sysfs-gpio.
+
+   New developments should use the chardev.rst, and existing developments are
+   encouraged to migrate as soon as possible, as this API will be removed
+   in the future.
+
+   This interface will continue to be maintained for the migration period,
+   but new features will only be added to the new API.
+
+The obsolete sysfs ABI
+----------------------
+Platforms which use the "gpiolib" implementors framework may choose to
+configure a sysfs user interface to GPIOs. This is different from the
+debugfs interface, since it provides control over GPIO direction and
+value instead of just showing a gpio state summary. Plus, it could be
+present on production systems without debugging support.
+
+Given appropriate hardware documentation for the system, userspace could
+know for example that GPIO #23 controls the write protect line used to
+protect boot loader segments in flash memory. System upgrade procedures
+may need to temporarily remove that protection, first importing a GPIO,
+then changing its output state, then updating the code before re-enabling
+the write protection. In normal use, GPIO #23 would never be touched,
+and the kernel would have no need to know about it.
+
+Again depending on appropriate hardware documentation, on some systems
+userspace GPIO can be used to determine system configuration data that
+standard kernels won't know about. And for some tasks, simple userspace
+GPIO drivers could be all that the system really needs.
+
+.. note::
+   Do NOT abuse sysfs to control hardware that has proper kernel drivers.
+   Please read Documentation/driver-api/gpio/drivers-on-gpio.rst
+   to avoid reinventing kernel wheels in userspace.
+
+   I MEAN IT. REALLY.
+
+Paths in Sysfs
+--------------
+There are three kinds of entries in /sys/class/gpio:
+
+   -	Control interfaces used to get userspace control over GPIOs;
+
+   -	GPIOs themselves; and
+
+   -	GPIO controllers ("gpio_chip" instances).
+
+That's in addition to standard files including the "device" symlink.
+
+The control interfaces are write-only:
+
+    /sys/class/gpio/
+
+	"export" ...
+		Userspace may ask the kernel to export control of
+		a GPIO to userspace by writing its number to this file.
+
+		Example:  "echo 19 > export" will create a "gpio19" node
+		for GPIO #19, if that's not requested by kernel code.
+
+	"unexport" ...
+		Reverses the effect of exporting to userspace.
+
+		Example:  "echo 19 > unexport" will remove a "gpio19"
+		node exported using the "export" file.
+
+GPIO signals have paths like /sys/class/gpio/gpio42/ (for GPIO #42)
+and have the following read/write attributes:
+
+    /sys/class/gpio/gpioN/
+
+	"direction" ...
+		reads as either "in" or "out". This value may
+		normally be written. Writing as "out" defaults to
+		initializing the value as low. To ensure glitch free
+		operation, values "low" and "high" may be written to
+		configure the GPIO as an output with that initial value.
+
+		Note that this attribute *will not exist* if the kernel
+		doesn't support changing the direction of a GPIO, or
+		it was exported by kernel code that didn't explicitly
+		allow userspace to reconfigure this GPIO's direction.
+
+	"value" ...
+		reads as either 0 (inactive) or 1 (active). If the GPIO
+		is configured as an output, this value may be written;
+		any nonzero value is treated as active.
+
+		If the pin can be configured as interrupt-generating interrupt
+		and if it has been configured to generate interrupts (see the
+		description of "edge"), you can poll(2) on that file and
+		poll(2) will return whenever the interrupt was triggered. If
+		you use poll(2), set the events POLLPRI and POLLERR. If you
+		use select(2), set the file descriptor in exceptfds. After
+		poll(2) returns, use pread(2) to read the value at offset
+		zero. Alternatively, either lseek(2) to the beginning of the
+		sysfs file and read the new value or close the file and
+		re-open it to read the value.
+
+	"edge" ...
+		reads as either "none", "rising", "falling", or
+		"both". Write these strings to select the signal edge(s)
+		that will make poll(2) on the "value" file return.
+
+		This file exists only if the pin can be configured as an
+		interrupt generating input pin.
+
+	"active_low" ...
+		reads as either 0 (false) or 1 (true). Write
+		any nonzero value to invert the value attribute both
+		for reading and writing. Existing and subsequent
+		poll(2) support configuration via the edge attribute
+		for "rising" and "falling" edges will follow this
+		setting.
+
+GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the
+controller implementing GPIOs starting at #42) and have the following
+read-only attributes:
+
+    /sys/class/gpio/gpiochipN/
+
+	"base" ...
+		same as N, the first GPIO managed by this chip
+
+	"label" ...
+		provided for diagnostics (not always unique)
+
+	"ngpio" ...
+		how many GPIOs this manages (N to N + ngpio - 1)
+
+Board documentation should in most cases cover what GPIOs are used for
+what purposes. However, those numbers are not always stable; GPIOs on
+a daughtercard might be different depending on the base board being used,
+or other cards in the stack. In such cases, you may need to use the
+gpiochip nodes (possibly in conjunction with schematics) to determine
+the correct GPIO number to use for a given signal.
+
+
+Exporting from Kernel code
+--------------------------
+Kernel code can explicitly manage exports of GPIOs which have already been
+requested using gpio_request()::
+
+	/* export the GPIO to userspace */
+	int gpiod_export(struct gpio_desc *desc, bool direction_may_change);
+
+	/* reverse gpiod_export() */
+	void gpiod_unexport(struct gpio_desc *desc);
+
+	/* create a sysfs link to an exported GPIO node */
+	int gpiod_export_link(struct device *dev, const char *name,
+		      struct gpio_desc *desc);
+
+After a kernel driver requests a GPIO, it may only be made available in
+the sysfs interface by gpiod_export(). The driver can control whether the
+signal direction may change. This helps drivers prevent userspace code
+from accidentally clobbering important system state.
+
+This explicit exporting can help with debugging (by making some kinds
+of experiments easier), or can provide an always-there interface that's
+suitable for documenting as part of a board support package.
+
+After the GPIO has been exported, gpiod_export_link() allows creating
+symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
+use this to provide the interface under their own device in sysfs with
+a descriptive name.