Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 985 insertions, 0 deletions

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
new file mode 100644
index 000000000..90c70d8d1
--- /dev/null
+++ b/drivers/tty/tty_ioctl.c
@@ -0,0 +1,985 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *
+ * Modified by Fred N. van Kempen, 01/29/93, to add line disciplines
+ * which can be dynamically activated and de-activated by the line
+ * discipline handling modules (like SLIP).
+ */
+
+#include <linux/bits.h>
+#include <linux/types.h>
+#include <linux/termios.h>
+#include <linux/errno.h>
+#include <linux/sched/signal.h>
+#include <linux/kernel.h>
+#include <linux/major.h>
+#include <linux/tty.h>
+#include <linux/fcntl.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/bitops.h>
+#include <linux/mutex.h>
+#include <linux/compat.h>
+#include <linux/termios_internal.h>
+#include "tty.h"
+
+#include <asm/io.h>
+#include <linux/uaccess.h>
+
+#undef	DEBUG
+
+/*
+ * Internal flag options for termios setting behavior
+ */
+#define TERMIOS_FLUSH	BIT(0)
+#define TERMIOS_WAIT	BIT(1)
+#define TERMIOS_TERMIO	BIT(2)
+#define TERMIOS_OLD	BIT(3)
+
+/**
+ * tty_chars_in_buffer - characters pending
+ * @tty: terminal
+ *
+ * Returns: the number of bytes of data in the device private output queue. If
+ * no private method is supplied there is assumed to be no queue on the device.
+ */
+unsigned int tty_chars_in_buffer(struct tty_struct *tty)
+{
+	if (tty->ops->chars_in_buffer)
+		return tty->ops->chars_in_buffer(tty);
+	return 0;
+}
+EXPORT_SYMBOL(tty_chars_in_buffer);
+
+/**
+ * tty_write_room - write queue space
+ * @tty: terminal
+ *
+ * Returns: the number of bytes that can be queued to this device at the present
+ * time. The result should be treated as a guarantee and the driver cannot
+ * offer a value it later shrinks by more than the number of bytes written. If
+ * no method is provided, 2K is always returned and data may be lost as there
+ * will be no flow control.
+ */
+unsigned int tty_write_room(struct tty_struct *tty)
+{
+	if (tty->ops->write_room)
+		return tty->ops->write_room(tty);
+	return 2048;
+}
+EXPORT_SYMBOL(tty_write_room);
+
+/**
+ * tty_driver_flush_buffer - discard internal buffer
+ * @tty: terminal
+ *
+ * Discard the internal output buffer for this device. If no method is provided,
+ * then either the buffer cannot be hardware flushed or there is no buffer
+ * driver side.
+ */
+void tty_driver_flush_buffer(struct tty_struct *tty)
+{
+	if (tty->ops->flush_buffer)
+		tty->ops->flush_buffer(tty);
+}
+EXPORT_SYMBOL(tty_driver_flush_buffer);
+
+/**
+ * tty_unthrottle - flow control
+ * @tty: terminal
+ *
+ * Indicate that a @tty may continue transmitting data down the stack. Takes
+ * the &tty_struct->termios_rwsem to protect against parallel
+ * throttle/unthrottle and also to ensure the driver can consistently reference
+ * its own termios data at this point when implementing software flow control.
+ *
+ * Drivers should however remember that the stack can issue a throttle, then
+ * change flow control method, then unthrottle.
+ */
+void tty_unthrottle(struct tty_struct *tty)
+{
+	down_write(&tty->termios_rwsem);
+	if (test_and_clear_bit(TTY_THROTTLED, &tty->flags) &&
+	    tty->ops->unthrottle)
+		tty->ops->unthrottle(tty);
+	tty->flow_change = TTY_FLOW_NO_CHANGE;
+	up_write(&tty->termios_rwsem);
+}
+EXPORT_SYMBOL(tty_unthrottle);
+
+/**
+ * tty_throttle_safe - flow control
+ * @tty: terminal
+ *
+ * Indicate that a @tty should stop transmitting data down the stack.
+ * tty_throttle_safe() will only attempt throttle if @tty->flow_change is
+ * %TTY_THROTTLE_SAFE. Prevents an accidental throttle due to race conditions
+ * when throttling is conditional on factors evaluated prior to throttling.
+ *
+ * Returns: %true if @tty is throttled (or was already throttled)
+ */
+bool tty_throttle_safe(struct tty_struct *tty)
+{
+	guard(mutex)(&tty->throttle_mutex);
+
+	if (tty_throttled(tty))
+		return true;
+
+	if (tty->flow_change != TTY_THROTTLE_SAFE)
+		return false;
+
+	set_bit(TTY_THROTTLED, &tty->flags);
+	if (tty->ops->throttle)
+		tty->ops->throttle(tty);
+
+	return true;
+}
+
+/**
+ * tty_unthrottle_safe - flow control
+ * @tty: terminal
+ *
+ * Similar to tty_unthrottle() but will only attempt unthrottle if
+ * @tty->flow_change is %TTY_UNTHROTTLE_SAFE. Prevents an accidental unthrottle
+ * due to race conditions when unthrottling is conditional on factors evaluated
+ * prior to unthrottling.
+ *
+ * Returns: %true if @tty is unthrottled (or was already unthrottled)
+ */
+bool tty_unthrottle_safe(struct tty_struct *tty)
+{
+	guard(mutex)(&tty->throttle_mutex);
+
+	if (!tty_throttled(tty))
+		return true;
+
+	if (tty->flow_change != TTY_UNTHROTTLE_SAFE)
+		return false;
+
+	clear_bit(TTY_THROTTLED, &tty->flags);
+	if (tty->ops->unthrottle)
+		tty->ops->unthrottle(tty);
+
+	return true;
+}
+
+/**
+ * tty_wait_until_sent - wait for I/O to finish
+ * @tty: tty we are waiting for
+ * @timeout: how long we will wait
+ *
+ * Wait for characters pending in a tty driver to hit the wire, or for a
+ * timeout to occur (eg due to flow control).
+ *
+ * Locking: none
+ */
+
+void tty_wait_until_sent(struct tty_struct *tty, long timeout)
+{
+	if (!timeout)
+		timeout = MAX_SCHEDULE_TIMEOUT;
+
+	timeout = wait_event_interruptible_timeout(tty->write_wait,
+			!tty_chars_in_buffer(tty), timeout);
+	if (timeout <= 0)
+		return;
+
+	if (timeout == MAX_SCHEDULE_TIMEOUT)
+		timeout = 0;
+
+	if (tty->ops->wait_until_sent)
+		tty->ops->wait_until_sent(tty, timeout);
+}
+EXPORT_SYMBOL(tty_wait_until_sent);
+
+
+/*
+ *		Termios Helper Methods
+ */
+
+static void unset_locked_termios(struct tty_struct *tty, const struct ktermios *old)
+{
+	struct ktermios *termios = &tty->termios;
+	struct ktermios *locked  = &tty->termios_locked;
+	int	i;
+
+#define NOSET_MASK(x, y, z) (x = ((x) & ~(z)) | ((y) & (z)))
+
+	NOSET_MASK(termios->c_iflag, old->c_iflag, locked->c_iflag);
+	NOSET_MASK(termios->c_oflag, old->c_oflag, locked->c_oflag);
+	NOSET_MASK(termios->c_cflag, old->c_cflag, locked->c_cflag);
+	NOSET_MASK(termios->c_lflag, old->c_lflag, locked->c_lflag);
+	termios->c_line = locked->c_line ? old->c_line : termios->c_line;
+	for (i = 0; i < NCCS; i++)
+		termios->c_cc[i] = locked->c_cc[i] ?
+			old->c_cc[i] : termios->c_cc[i];
+	/* FIXME: What should we do for i/ospeed */
+}
+
+/**
+ * tty_termios_copy_hw - copy hardware settings
+ * @new: new termios
+ * @old: old termios
+ *
+ * Propagate the hardware specific terminal setting bits from the @old termios
+ * structure to the @new one. This is used in cases where the hardware does not
+ * support reconfiguration or as a helper in some cases where only minimal
+ * reconfiguration is supported.
+ */
+void tty_termios_copy_hw(struct ktermios *new, const struct ktermios *old)
+{
+	/* The bits a dumb device handles in software. Smart devices need
+	   to always provide a set_termios method */
+	new->c_cflag &= HUPCL | CREAD | CLOCAL;
+	new->c_cflag |= old->c_cflag & ~(HUPCL | CREAD | CLOCAL);
+	new->c_ispeed = old->c_ispeed;
+	new->c_ospeed = old->c_ospeed;
+}
+EXPORT_SYMBOL(tty_termios_copy_hw);
+
+/**
+ * tty_termios_hw_change - check for setting change
+ * @a: termios
+ * @b: termios to compare
+ *
+ * Check if any of the bits that affect a dumb device have changed between the
+ * two termios structures, or a speed change is needed.
+ *
+ * Returns: %true if change is needed
+ */
+bool tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b)
+{
+	if (a->c_ispeed != b->c_ispeed || a->c_ospeed != b->c_ospeed)
+		return true;
+	if ((a->c_cflag ^ b->c_cflag) & ~(HUPCL | CREAD | CLOCAL))
+		return true;
+	return false;
+}
+EXPORT_SYMBOL(tty_termios_hw_change);
+
+/**
+ * tty_get_char_size - get size of a character
+ * @cflag: termios cflag value
+ *
+ * Returns: size (in bits) of a character depending on @cflag's %CSIZE setting
+ */
+unsigned char tty_get_char_size(unsigned int cflag)
+{
+	switch (cflag & CSIZE) {
+	case CS5:
+		return 5;
+	case CS6:
+		return 6;
+	case CS7:
+		return 7;
+	case CS8:
+	default:
+		return 8;
+	}
+}
+EXPORT_SYMBOL_GPL(tty_get_char_size);
+
+/**
+ * tty_get_frame_size - get size of a frame
+ * @cflag: termios cflag value
+ *
+ * Get the size (in bits) of a frame depending on @cflag's %CSIZE, %CSTOPB, and
+ * %PARENB setting. The result is a sum of character size, start and stop bits
+ * -- one bit each -- second stop bit (if set), and parity bit (if set).
+ *
+ * Returns: size (in bits) of a frame depending on @cflag's setting.
+ */
+unsigned char tty_get_frame_size(unsigned int cflag)
+{
+	unsigned char bits = 2 + tty_get_char_size(cflag);
+
+	if (cflag & CSTOPB)
+		bits++;
+	if (cflag & PARENB)
+		bits++;
+	if (cflag & ADDRB)
+		bits++;
+
+	return bits;
+}
+EXPORT_SYMBOL_GPL(tty_get_frame_size);
+
+/**
+ * tty_set_termios - update termios values
+ * @tty: tty to update
+ * @new_termios: desired new value
+ *
+ * Perform updates to the termios values set on this @tty. A master pty's
+ * termios should never be set.
+ *
+ * Locking: &tty_struct->termios_rwsem
+ */
+int tty_set_termios(struct tty_struct *tty, struct ktermios *new_termios)
+{
+	struct ktermios old_termios;
+	struct tty_ldisc *ld;
+
+	WARN_ON(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+		tty->driver->subtype == PTY_TYPE_MASTER);
+	/*
+	 *	Perform the actual termios internal changes under lock.
+	 */
+
+
+	/* FIXME: we need to decide on some locking/ordering semantics
+	   for the set_termios notification eventually */
+	down_write(&tty->termios_rwsem);
+	old_termios = tty->termios;
+	tty->termios = *new_termios;
+	unset_locked_termios(tty, &old_termios);
+	/* Reset any ADDRB changes, ADDRB is changed through ->rs485_config() */
+	tty->termios.c_cflag ^= (tty->termios.c_cflag ^ old_termios.c_cflag) & ADDRB;
+
+	if (tty->ops->set_termios)
+		tty->ops->set_termios(tty, &old_termios);
+	else
+		tty_termios_copy_hw(&tty->termios, &old_termios);
+
+	ld = tty_ldisc_ref(tty);
+	if (ld != NULL) {
+		if (ld->ops->set_termios)
+			ld->ops->set_termios(tty, &old_termios);
+		tty_ldisc_deref(ld);
+	}
+	up_write(&tty->termios_rwsem);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(tty_set_termios);
+
+
+/*
+ * Translate a "termio" structure into a "termios". Ugh.
+ */
+__weak int user_termio_to_kernel_termios(struct ktermios *termios,
+						struct termio __user *termio)
+{
+	struct termio v;
+
+	if (copy_from_user(&v, termio, sizeof(struct termio)))
+		return -EFAULT;
+
+	termios->c_iflag = (0xffff0000 & termios->c_iflag) | v.c_iflag;
+	termios->c_oflag = (0xffff0000 & termios->c_oflag) | v.c_oflag;
+	termios->c_cflag = (0xffff0000 & termios->c_cflag) | v.c_cflag;
+	termios->c_lflag = (0xffff0000 & termios->c_lflag) | v.c_lflag;
+	termios->c_line = (0xffff0000 & termios->c_lflag) | v.c_line;
+	memcpy(termios->c_cc, v.c_cc, NCC);
+	return 0;
+}
+
+/*
+ * Translate a "termios" structure into a "termio". Ugh.
+ */
+__weak int kernel_termios_to_user_termio(struct termio __user *termio,
+						struct ktermios *termios)
+{
+	struct termio v;
+	memset(&v, 0, sizeof(struct termio));
+	v.c_iflag = termios->c_iflag;
+	v.c_oflag = termios->c_oflag;
+	v.c_cflag = termios->c_cflag;
+	v.c_lflag = termios->c_lflag;
+	v.c_line = termios->c_line;
+	memcpy(v.c_cc, termios->c_cc, NCC);
+	return copy_to_user(termio, &v, sizeof(struct termio));
+}
+
+#ifdef TCGETS2
+__weak int user_termios_to_kernel_termios(struct ktermios *k,
+						 struct termios2 __user *u)
+{
+	return copy_from_user(k, u, sizeof(struct termios2));
+}
+__weak int kernel_termios_to_user_termios(struct termios2 __user *u,
+						 struct ktermios *k)
+{
+	return copy_to_user(u, k, sizeof(struct termios2));
+}
+__weak int user_termios_to_kernel_termios_1(struct ktermios *k,
+						   struct termios __user *u)
+{
+	return copy_from_user(k, u, sizeof(struct termios));
+}
+__weak int kernel_termios_to_user_termios_1(struct termios __user *u,
+						   struct ktermios *k)
+{
+	return copy_to_user(u, k, sizeof(struct termios));
+}
+
+#else
+
+__weak int user_termios_to_kernel_termios(struct ktermios *k,
+						 struct termios __user *u)
+{
+	return copy_from_user(k, u, sizeof(struct termios));
+}
+__weak int kernel_termios_to_user_termios(struct termios __user *u,
+						 struct ktermios *k)
+{
+	return copy_to_user(u, k, sizeof(struct termios));
+}
+#endif /* TCGETS2 */
+
+/**
+ * set_termios - set termios values for a tty
+ * @tty: terminal device
+ * @arg: user data
+ * @opt: option information
+ *
+ * Helper function to prepare termios data and run necessary other functions
+ * before using tty_set_termios() to do the actual changes.
+ *
+ * Locking: called functions take &tty_struct->ldisc_sem and
+ * &tty_struct->termios_rwsem locks
+ *
+ * Returns: 0 on success, an error otherwise
+ */
+static int set_termios(struct tty_struct *tty, void __user *arg, int opt)
+{
+	struct ktermios tmp_termios;
+	struct tty_ldisc *ld;
+	int retval = tty_check_change(tty);
+
+	if (retval)
+		return retval;
+
+	down_read(&tty->termios_rwsem);
+	tmp_termios = tty->termios;
+	up_read(&tty->termios_rwsem);
+
+	if (opt & TERMIOS_TERMIO) {
+		if (user_termio_to_kernel_termios(&tmp_termios,
+						(struct termio __user *)arg))
+			return -EFAULT;
+#ifdef TCGETS2
+	} else if (opt & TERMIOS_OLD) {
+		if (user_termios_to_kernel_termios_1(&tmp_termios,
+						(struct termios __user *)arg))
+			return -EFAULT;
+	} else {
+		if (user_termios_to_kernel_termios(&tmp_termios,
+						(struct termios2 __user *)arg))
+			return -EFAULT;
+	}
+#else
+	} else if (user_termios_to_kernel_termios(&tmp_termios,
+					(struct termios __user *)arg))
+		return -EFAULT;
+#endif
+
+	/* If old style Bfoo values are used then load c_ispeed/c_ospeed
+	 * with the real speed so its unconditionally usable */
+	tmp_termios.c_ispeed = tty_termios_input_baud_rate(&tmp_termios);
+	tmp_termios.c_ospeed = tty_termios_baud_rate(&tmp_termios);
+
+	if (opt & (TERMIOS_FLUSH|TERMIOS_WAIT)) {
+retry_write_wait:
+		retval = wait_event_interruptible(tty->write_wait, !tty_chars_in_buffer(tty));
+		if (retval < 0)
+			return retval;
+
+		if (tty_write_lock(tty, false) < 0)
+			goto retry_write_wait;
+
+		/* Racing writer? */
+		if (tty_chars_in_buffer(tty)) {
+			tty_write_unlock(tty);
+			goto retry_write_wait;
+		}
+
+		ld = tty_ldisc_ref(tty);
+		if (ld != NULL) {
+			if ((opt & TERMIOS_FLUSH) && ld->ops->flush_buffer)
+				ld->ops->flush_buffer(tty);
+			tty_ldisc_deref(ld);
+		}
+
+		if ((opt & TERMIOS_WAIT) && tty->ops->wait_until_sent) {
+			tty->ops->wait_until_sent(tty, 0);
+			if (signal_pending(current)) {
+				tty_write_unlock(tty);
+				return -ERESTARTSYS;
+			}
+		}
+
+		tty_set_termios(tty, &tmp_termios);
+
+		tty_write_unlock(tty);
+	} else {
+		tty_set_termios(tty, &tmp_termios);
+	}
+
+	/* FIXME: Arguably if tmp_termios == tty->termios AND the
+	   actual requested termios was not tmp_termios then we may
+	   want to return an error as no user requested change has
+	   succeeded */
+	return 0;
+}
+
+static void copy_termios(struct tty_struct *tty, struct ktermios *kterm)
+{
+	down_read(&tty->termios_rwsem);
+	*kterm = tty->termios;
+	up_read(&tty->termios_rwsem);
+}
+
+static void copy_termios_locked(struct tty_struct *tty, struct ktermios *kterm)
+{
+	down_read(&tty->termios_rwsem);
+	*kterm = tty->termios_locked;
+	up_read(&tty->termios_rwsem);
+}
+
+static int get_termio(struct tty_struct *tty, struct termio __user *termio)
+{
+	struct ktermios kterm;
+	copy_termios(tty, &kterm);
+	if (kernel_termios_to_user_termio(termio, &kterm))
+		return -EFAULT;
+	return 0;
+}
+
+#ifdef TIOCGETP
+/*
+ * These are deprecated, but there is limited support..
+ *
+ * The "sg_flags" translation is a joke..
+ */
+static int get_sgflags(struct tty_struct *tty)
+{
+	int flags = 0;
+
+	if (!L_ICANON(tty)) {
+		if (L_ISIG(tty))
+			flags |= 0x02;		/* cbreak */
+		else
+			flags |= 0x20;		/* raw */
+	}
+	if (L_ECHO(tty))
+		flags |= 0x08;			/* echo */
+	if (O_OPOST(tty))
+		if (O_ONLCR(tty))
+			flags |= 0x10;		/* crmod */
+	return flags;
+}
+
+static int get_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)
+{
+	struct sgttyb tmp;
+
+	down_read(&tty->termios_rwsem);
+	tmp.sg_ispeed = tty->termios.c_ispeed;
+	tmp.sg_ospeed = tty->termios.c_ospeed;
+	tmp.sg_erase = tty->termios.c_cc[VERASE];
+	tmp.sg_kill = tty->termios.c_cc[VKILL];
+	tmp.sg_flags = get_sgflags(tty);
+	up_read(&tty->termios_rwsem);
+
+	return copy_to_user(sgttyb, &tmp, sizeof(tmp)) ? -EFAULT : 0;
+}
+
+static void set_sgflags(struct ktermios *termios, int flags)
+{
+	termios->c_iflag = ICRNL | IXON;
+	termios->c_oflag = 0;
+	termios->c_lflag = ISIG | ICANON;
+	if (flags & 0x02) {	/* cbreak */
+		termios->c_iflag = 0;
+		termios->c_lflag &= ~ICANON;
+	}
+	if (flags & 0x08) {		/* echo */
+		termios->c_lflag |= ECHO | ECHOE | ECHOK |
+				    ECHOCTL | ECHOKE | IEXTEN;
+	}
+	if (flags & 0x10) {		/* crmod */
+		termios->c_oflag |= OPOST | ONLCR;
+	}
+	if (flags & 0x20) {	/* raw */
+		termios->c_iflag = 0;
+		termios->c_lflag &= ~(ISIG | ICANON);
+	}
+	if (!(termios->c_lflag & ICANON)) {
+		termios->c_cc[VMIN] = 1;
+		termios->c_cc[VTIME] = 0;
+	}
+}
+
+/**
+ * set_sgttyb - set legacy terminal values
+ * @tty: tty structure
+ * @sgttyb: pointer to old style terminal structure
+ *
+ * Updates a terminal from the legacy BSD style terminal information structure.
+ *
+ * Locking: &tty_struct->termios_rwsem
+ *
+ * Returns: 0 on success, an error otherwise
+ */
+static int set_sgttyb(struct tty_struct *tty, struct sgttyb __user *sgttyb)
+{
+	int retval;
+	struct sgttyb tmp;
+	struct ktermios termios;
+
+	retval = tty_check_change(tty);
+	if (retval)
+		return retval;
+
+	if (copy_from_user(&tmp, sgttyb, sizeof(tmp)))
+		return -EFAULT;
+
+	down_write(&tty->termios_rwsem);
+	termios = tty->termios;
+	termios.c_cc[VERASE] = tmp.sg_erase;
+	termios.c_cc[VKILL] = tmp.sg_kill;
+	set_sgflags(&termios, tmp.sg_flags);
+	/* Try and encode into Bfoo format */
+	tty_termios_encode_baud_rate(&termios, termios.c_ispeed,
+						termios.c_ospeed);
+	up_write(&tty->termios_rwsem);
+	tty_set_termios(tty, &termios);
+	return 0;
+}
+#endif
+
+#ifdef TIOCGETC
+static int get_tchars(struct tty_struct *tty, struct tchars __user *tchars)
+{
+	struct tchars tmp;
+
+	down_read(&tty->termios_rwsem);
+	tmp.t_intrc = tty->termios.c_cc[VINTR];
+	tmp.t_quitc = tty->termios.c_cc[VQUIT];
+	tmp.t_startc = tty->termios.c_cc[VSTART];
+	tmp.t_stopc = tty->termios.c_cc[VSTOP];
+	tmp.t_eofc = tty->termios.c_cc[VEOF];
+	tmp.t_brkc = tty->termios.c_cc[VEOL2];	/* what is brkc anyway? */
+	up_read(&tty->termios_rwsem);
+	return copy_to_user(tchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
+}
+
+static int set_tchars(struct tty_struct *tty, struct tchars __user *tchars)
+{
+	struct tchars tmp;
+
+	if (copy_from_user(&tmp, tchars, sizeof(tmp)))
+		return -EFAULT;
+	down_write(&tty->termios_rwsem);
+	tty->termios.c_cc[VINTR] = tmp.t_intrc;
+	tty->termios.c_cc[VQUIT] = tmp.t_quitc;
+	tty->termios.c_cc[VSTART] = tmp.t_startc;
+	tty->termios.c_cc[VSTOP] = tmp.t_stopc;
+	tty->termios.c_cc[VEOF] = tmp.t_eofc;
+	tty->termios.c_cc[VEOL2] = tmp.t_brkc;	/* what is brkc anyway? */
+	up_write(&tty->termios_rwsem);
+	return 0;
+}
+#endif
+
+#ifdef TIOCGLTC
+static int get_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)
+{
+	struct ltchars tmp;
+
+	down_read(&tty->termios_rwsem);
+	tmp.t_suspc = tty->termios.c_cc[VSUSP];
+	/* what is dsuspc anyway? */
+	tmp.t_dsuspc = tty->termios.c_cc[VSUSP];
+	tmp.t_rprntc = tty->termios.c_cc[VREPRINT];
+	/* what is flushc anyway? */
+	tmp.t_flushc = tty->termios.c_cc[VEOL2];
+	tmp.t_werasc = tty->termios.c_cc[VWERASE];
+	tmp.t_lnextc = tty->termios.c_cc[VLNEXT];
+	up_read(&tty->termios_rwsem);
+	return copy_to_user(ltchars, &tmp, sizeof(tmp)) ? -EFAULT : 0;
+}
+
+static int set_ltchars(struct tty_struct *tty, struct ltchars __user *ltchars)
+{
+	struct ltchars tmp;
+
+	if (copy_from_user(&tmp, ltchars, sizeof(tmp)))
+		return -EFAULT;
+
+	down_write(&tty->termios_rwsem);
+	tty->termios.c_cc[VSUSP] = tmp.t_suspc;
+	/* what is dsuspc anyway? */
+	tty->termios.c_cc[VEOL2] = tmp.t_dsuspc;
+	tty->termios.c_cc[VREPRINT] = tmp.t_rprntc;
+	/* what is flushc anyway? */
+	tty->termios.c_cc[VEOL2] = tmp.t_flushc;
+	tty->termios.c_cc[VWERASE] = tmp.t_werasc;
+	tty->termios.c_cc[VLNEXT] = tmp.t_lnextc;
+	up_write(&tty->termios_rwsem);
+	return 0;
+}
+#endif
+
+/**
+ * tty_change_softcar - carrier change ioctl helper
+ * @tty: tty to update
+ * @enable: enable/disable %CLOCAL
+ *
+ * Perform a change to the %CLOCAL state and call into the driver layer to make
+ * it visible.
+ *
+ * Locking: &tty_struct->termios_rwsem.
+ *
+ * Returns: 0 on success, an error otherwise
+ */
+static int tty_change_softcar(struct tty_struct *tty, bool enable)
+{
+	int ret = 0;
+	struct ktermios old;
+	tcflag_t bit = enable ? CLOCAL : 0;
+
+	down_write(&tty->termios_rwsem);
+	old = tty->termios;
+	tty->termios.c_cflag &= ~CLOCAL;
+	tty->termios.c_cflag |= bit;
+	if (tty->ops->set_termios)
+		tty->ops->set_termios(tty, &old);
+	if (C_CLOCAL(tty) != bit)
+		ret = -EINVAL;
+	up_write(&tty->termios_rwsem);
+	return ret;
+}
+
+/**
+ * tty_mode_ioctl - mode related ioctls
+ * @tty: tty for the ioctl
+ * @cmd: command
+ * @arg: ioctl argument
+ *
+ * Perform non-line discipline specific mode control ioctls. This is designed
+ * to be called by line disciplines to ensure they provide consistent mode
+ * setting.
+ */
+int tty_mode_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
+{
+	struct tty_struct *real_tty;
+	void __user *p = (void __user *)arg;
+	int ret = 0;
+	struct ktermios kterm;
+
+	if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+	    tty->driver->subtype == PTY_TYPE_MASTER)
+		real_tty = tty->link;
+	else
+		real_tty = tty;
+
+	switch (cmd) {
+#ifdef TIOCGETP
+	case TIOCGETP:
+		return get_sgttyb(real_tty, (struct sgttyb __user *) arg);
+	case TIOCSETP:
+	case TIOCSETN:
+		return set_sgttyb(real_tty, (struct sgttyb __user *) arg);
+#endif
+#ifdef TIOCGETC
+	case TIOCGETC:
+		return get_tchars(real_tty, p);
+	case TIOCSETC:
+		return set_tchars(real_tty, p);
+#endif
+#ifdef TIOCGLTC
+	case TIOCGLTC:
+		return get_ltchars(real_tty, p);
+	case TIOCSLTC:
+		return set_ltchars(real_tty, p);
+#endif
+	case TCSETSF:
+		return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_OLD);
+	case TCSETSW:
+		return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_OLD);
+	case TCSETS:
+		return set_termios(real_tty, p, TERMIOS_OLD);
+#ifndef TCGETS2
+	case TCGETS:
+		copy_termios(real_tty, &kterm);
+		if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))
+			ret = -EFAULT;
+		return ret;
+#else
+	case TCGETS:
+		copy_termios(real_tty, &kterm);
+		if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))
+			ret = -EFAULT;
+		return ret;
+	case TCGETS2:
+		copy_termios(real_tty, &kterm);
+		if (kernel_termios_to_user_termios((struct termios2 __user *)arg, &kterm))
+			ret = -EFAULT;
+		return ret;
+	case TCSETSF2:
+		return set_termios(real_tty, p,  TERMIOS_FLUSH | TERMIOS_WAIT);
+	case TCSETSW2:
+		return set_termios(real_tty, p, TERMIOS_WAIT);
+	case TCSETS2:
+		return set_termios(real_tty, p, 0);
+#endif
+	case TCGETA:
+		return get_termio(real_tty, p);
+	case TCSETAF:
+		return set_termios(real_tty, p, TERMIOS_FLUSH | TERMIOS_WAIT | TERMIOS_TERMIO);
+	case TCSETAW:
+		return set_termios(real_tty, p, TERMIOS_WAIT | TERMIOS_TERMIO);
+	case TCSETA:
+		return set_termios(real_tty, p, TERMIOS_TERMIO);
+#ifndef TCGETS2
+	case TIOCGLCKTRMIOS:
+		copy_termios_locked(real_tty, &kterm);
+		if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))
+			ret = -EFAULT;
+		return ret;
+	case TIOCSLCKTRMIOS:
+		if (!checkpoint_restore_ns_capable(&init_user_ns))
+			return -EPERM;
+		copy_termios_locked(real_tty, &kterm);
+		if (user_termios_to_kernel_termios(&kterm,
+					       (struct termios __user *) arg))
+			return -EFAULT;
+		down_write(&real_tty->termios_rwsem);
+		real_tty->termios_locked = kterm;
+		up_write(&real_tty->termios_rwsem);
+		return 0;
+#else
+	case TIOCGLCKTRMIOS:
+		copy_termios_locked(real_tty, &kterm);
+		if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))
+			ret = -EFAULT;
+		return ret;
+	case TIOCSLCKTRMIOS:
+		if (!checkpoint_restore_ns_capable(&init_user_ns))
+			return -EPERM;
+		copy_termios_locked(real_tty, &kterm);
+		if (user_termios_to_kernel_termios_1(&kterm,
+					       (struct termios __user *) arg))
+			return -EFAULT;
+		down_write(&real_tty->termios_rwsem);
+		real_tty->termios_locked = kterm;
+		up_write(&real_tty->termios_rwsem);
+		return ret;
+#endif
+#ifdef TCGETX
+	case TCGETX:
+	case TCSETX:
+	case TCSETXW:
+	case TCSETXF:
+		return -ENOTTY;
+#endif
+	case TIOCGSOFTCAR:
+		copy_termios(real_tty, &kterm);
+		ret = put_user((kterm.c_cflag & CLOCAL) ? 1 : 0,
+						(int __user *)arg);
+		return ret;
+	case TIOCSSOFTCAR:
+		if (get_user(arg, (unsigned int __user *) arg))
+			return -EFAULT;
+		return tty_change_softcar(real_tty, arg);
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+EXPORT_SYMBOL_GPL(tty_mode_ioctl);
+
+
+/* Caller guarantees ldisc reference is held */
+static int __tty_perform_flush(struct tty_struct *tty, unsigned long arg)
+{
+	struct tty_ldisc *ld = tty->ldisc;
+
+	switch (arg) {
+	case TCIFLUSH:
+		if (ld && ld->ops->flush_buffer) {
+			ld->ops->flush_buffer(tty);
+			tty_unthrottle(tty);
+		}
+		break;
+	case TCIOFLUSH:
+		if (ld && ld->ops->flush_buffer) {
+			ld->ops->flush_buffer(tty);
+			tty_unthrottle(tty);
+		}
+		fallthrough;
+	case TCOFLUSH:
+		tty_driver_flush_buffer(tty);
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
+}
+
+int tty_perform_flush(struct tty_struct *tty, unsigned long arg)
+{
+	struct tty_ldisc *ld;
+	int retval = tty_check_change(tty);
+	if (retval)
+		return retval;
+
+	ld = tty_ldisc_ref_wait(tty);
+	retval = __tty_perform_flush(tty, arg);
+	if (ld)
+		tty_ldisc_deref(ld);
+	return retval;
+}
+EXPORT_SYMBOL_GPL(tty_perform_flush);
+
+int n_tty_ioctl_helper(struct tty_struct *tty, unsigned int cmd,
+		unsigned long arg)
+{
+	int retval;
+
+	switch (cmd) {
+	case TCXONC:
+		retval = tty_check_change(tty);
+		if (retval)
+			return retval;
+		switch (arg) {
+		case TCOOFF:
+			spin_lock_irq(&tty->flow.lock);
+			if (!tty->flow.tco_stopped) {
+				tty->flow.tco_stopped = true;
+				__stop_tty(tty);
+			}
+			spin_unlock_irq(&tty->flow.lock);
+			break;
+		case TCOON:
+			spin_lock_irq(&tty->flow.lock);
+			if (tty->flow.tco_stopped) {
+				tty->flow.tco_stopped = false;
+				__start_tty(tty);
+			}
+			spin_unlock_irq(&tty->flow.lock);
+			break;
+		case TCIOFF:
+			if (STOP_CHAR(tty) != __DISABLED_CHAR)
+				retval = tty_send_xchar(tty, STOP_CHAR(tty));
+			break;
+		case TCION:
+			if (START_CHAR(tty) != __DISABLED_CHAR)
+				retval = tty_send_xchar(tty, START_CHAR(tty));
+			break;
+		default:
+			return -EINVAL;
+		}
+		return retval;
+	case TCFLSH:
+		retval = tty_check_change(tty);
+		if (retval)
+			return retval;
+		return __tty_perform_flush(tty, arg);
+	default:
+		/* Try the mode commands */
+		return tty_mode_ioctl(tty, cmd, arg);
+	}
+}
+EXPORT_SYMBOL(n_tty_ioctl_helper);