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, 738 insertions, 0 deletions

diff --git a/drivers/comedi/comedi_buf.c b/drivers/comedi/comedi_buf.c
new file mode 100644
index 000000000..ed372619b
--- /dev/null
+++ b/drivers/comedi/comedi_buf.c
@@ -0,0 +1,738 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * comedi_buf.c
+ *
+ * COMEDI - Linux Control and Measurement Device Interface
+ * Copyright (C) 1997-2000 David A. Schleef <ds@schleef.org>
+ * Copyright (C) 2002 Frank Mori Hess <fmhess@users.sourceforge.net>
+ */
+
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
+#include <linux/comedi/comedidev.h>
+#include "comedi_internal.h"
+
+#ifdef PAGE_KERNEL_NOCACHE
+#define COMEDI_PAGE_PROTECTION		PAGE_KERNEL_NOCACHE
+#else
+#define COMEDI_PAGE_PROTECTION		PAGE_KERNEL
+#endif
+
+static void comedi_buf_map_kref_release(struct kref *kref)
+{
+	struct comedi_buf_map *bm =
+		container_of(kref, struct comedi_buf_map, refcount);
+	struct comedi_buf_page *buf;
+	unsigned int i;
+
+	if (bm->page_list) {
+		if (bm->dma_dir != DMA_NONE) {
+			for (i = 0; i < bm->n_pages; i++) {
+				buf = &bm->page_list[i];
+				dma_free_coherent(bm->dma_hw_dev, PAGE_SIZE,
+						  buf->virt_addr,
+						  buf->dma_addr);
+			}
+		} else {
+			for (i = 0; i < bm->n_pages; i++) {
+				buf = &bm->page_list[i];
+				ClearPageReserved(virt_to_page(buf->virt_addr));
+				free_page((unsigned long)buf->virt_addr);
+			}
+		}
+		vfree(bm->page_list);
+	}
+	if (bm->dma_dir != DMA_NONE)
+		put_device(bm->dma_hw_dev);
+	kfree(bm);
+}
+
+static void __comedi_buf_free(struct comedi_device *dev,
+			      struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_map *bm;
+	unsigned long flags;
+
+	async->prealloc_bufsz = 0;
+	spin_lock_irqsave(&s->spin_lock, flags);
+	bm = async->buf_map;
+	async->buf_map = NULL;
+	spin_unlock_irqrestore(&s->spin_lock, flags);
+	comedi_buf_map_put(bm);
+}
+
+static struct comedi_buf_map *
+comedi_buf_map_alloc(struct comedi_device *dev, enum dma_data_direction dma_dir,
+		     unsigned int n_pages)
+{
+	struct comedi_buf_map *bm;
+	struct comedi_buf_page *buf;
+	unsigned int i;
+
+	bm = kzalloc_obj(*bm);
+	if (!bm)
+		return NULL;
+
+	kref_init(&bm->refcount);
+	bm->dma_dir = dma_dir;
+	if (bm->dma_dir != DMA_NONE) {
+		/* Need ref to hardware device to free buffer later. */
+		bm->dma_hw_dev = get_device(dev->hw_dev);
+	}
+
+	bm->page_list = vzalloc(sizeof(*buf) * n_pages);
+	if (!bm->page_list)
+		goto err;
+
+	if (bm->dma_dir != DMA_NONE) {
+		for (i = 0; i < n_pages; i++) {
+			buf = &bm->page_list[i];
+			buf->virt_addr =
+			    dma_alloc_coherent(bm->dma_hw_dev, PAGE_SIZE,
+					       &buf->dma_addr, GFP_KERNEL);
+			if (!buf->virt_addr)
+				break;
+		}
+	} else {
+		for (i = 0; i < n_pages; i++) {
+			buf = &bm->page_list[i];
+			buf->virt_addr = (void *)get_zeroed_page(GFP_KERNEL);
+			if (!buf->virt_addr)
+				break;
+
+			SetPageReserved(virt_to_page(buf->virt_addr));
+		}
+	}
+	bm->n_pages = i;
+	if (i < n_pages)
+		goto err;
+
+	return bm;
+
+err:
+	comedi_buf_map_put(bm);
+	return NULL;
+}
+
+static void __comedi_buf_alloc(struct comedi_device *dev,
+			       struct comedi_subdevice *s,
+			       unsigned int n_pages)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_map *bm;
+	unsigned long flags;
+
+	if (!IS_ENABLED(CONFIG_HAS_DMA) && s->async_dma_dir != DMA_NONE) {
+		dev_err(dev->class_dev,
+			"dma buffer allocation not supported\n");
+		return;
+	}
+
+	bm = comedi_buf_map_alloc(dev, s->async_dma_dir, n_pages);
+	if (!bm)
+		return;
+
+	spin_lock_irqsave(&s->spin_lock, flags);
+	async->buf_map = bm;
+	spin_unlock_irqrestore(&s->spin_lock, flags);
+	async->prealloc_bufsz = n_pages << PAGE_SHIFT;
+}
+
+void comedi_buf_map_get(struct comedi_buf_map *bm)
+{
+	if (bm)
+		kref_get(&bm->refcount);
+}
+
+int comedi_buf_map_put(struct comedi_buf_map *bm)
+{
+	if (bm)
+		return kref_put(&bm->refcount, comedi_buf_map_kref_release);
+	return 1;
+}
+
+/* helper for "access" vm operation */
+int comedi_buf_map_access(struct comedi_buf_map *bm, unsigned long offset,
+			  void *buf, int len, int write)
+{
+	unsigned int pgoff = offset_in_page(offset);
+	unsigned long pg = offset >> PAGE_SHIFT;
+	int done = 0;
+
+	while (done < len && pg < bm->n_pages) {
+		int l = min_t(int, len - done, PAGE_SIZE - pgoff);
+		void *b = bm->page_list[pg].virt_addr + pgoff;
+
+		if (write)
+			memcpy(b, buf, l);
+		else
+			memcpy(buf, b, l);
+		buf += l;
+		done += l;
+		pg++;
+		pgoff = 0;
+	}
+	return done;
+}
+
+/* returns s->async->buf_map and increments its kref refcount */
+struct comedi_buf_map *
+comedi_buf_map_from_subdev_get(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_map *bm = NULL;
+	unsigned long flags;
+
+	if (!async)
+		return NULL;
+
+	spin_lock_irqsave(&s->spin_lock, flags);
+	bm = async->buf_map;
+	/* only want it if buffer pages allocated */
+	if (bm && bm->n_pages)
+		comedi_buf_map_get(bm);
+	else
+		bm = NULL;
+	spin_unlock_irqrestore(&s->spin_lock, flags);
+
+	return bm;
+}
+
+bool comedi_buf_is_mmapped(struct comedi_subdevice *s)
+{
+	struct comedi_buf_map *bm = s->async->buf_map;
+
+	return bm && (kref_read(&bm->refcount) > 1);
+}
+
+int comedi_buf_alloc(struct comedi_device *dev, struct comedi_subdevice *s,
+		     unsigned long new_size)
+{
+	struct comedi_async *async = s->async;
+
+	lockdep_assert_held(&dev->mutex);
+
+	/* Round up new_size to multiple of PAGE_SIZE */
+	new_size = (new_size + PAGE_SIZE - 1) & PAGE_MASK;
+
+	/* if no change is required, do nothing */
+	if (async->prealloc_bufsz == new_size)
+		return 0;
+
+	/* deallocate old buffer */
+	__comedi_buf_free(dev, s);
+
+	/* allocate new buffer */
+	if (new_size) {
+		unsigned int n_pages = new_size >> PAGE_SHIFT;
+
+		__comedi_buf_alloc(dev, s, n_pages);
+		if (!async->prealloc_bufsz)
+			return -ENOMEM;
+	}
+
+	return 0;
+}
+
+void comedi_buf_reset(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+
+	async->buf_write_alloc_count = 0;
+	async->buf_write_count = 0;
+	async->buf_read_alloc_count = 0;
+	async->buf_read_count = 0;
+
+	async->buf_write_ptr = 0;
+	async->buf_read_ptr = 0;
+
+	async->cur_chan = 0;
+	async->scans_done = 0;
+	async->scan_progress = 0;
+	async->munge_chan = 0;
+	async->munge_count = 0;
+	async->munge_ptr = 0;
+
+	async->events = 0;
+}
+
+static unsigned int comedi_buf_write_n_unalloc(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+	unsigned int free_end = async->buf_read_count + async->prealloc_bufsz;
+
+	return free_end - async->buf_write_alloc_count;
+}
+
+unsigned int comedi_buf_write_n_available(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+	unsigned int free_end = async->buf_read_count + async->prealloc_bufsz;
+
+	return free_end - async->buf_write_count;
+}
+
+unsigned int _comedi_buf_write_alloc(struct comedi_subdevice *s,
+				     unsigned int nbytes)
+{
+	struct comedi_async *async = s->async;
+	unsigned int unalloc = comedi_buf_write_n_unalloc(s);
+
+	if (nbytes > unalloc)
+		nbytes = unalloc;
+
+	async->buf_write_alloc_count += nbytes;
+
+	/*
+	 * ensure the async buffer 'counts' are read and updated
+	 * before we write data to the write-alloc'ed buffer space
+	 */
+	smp_mb();
+
+	return nbytes;
+}
+
+/**
+ * comedi_buf_write_alloc() - Reserve buffer space for writing
+ * @s: COMEDI subdevice.
+ * @nbytes: Maximum space to reserve in bytes.
+ *
+ * Reserve up to @nbytes bytes of space to be written in the COMEDI acquisition
+ * data buffer associated with the subdevice.  The amount reserved is limited
+ * by the space available.
+ *
+ * Return: The amount of space reserved in bytes.
+ */
+unsigned int comedi_buf_write_alloc(struct comedi_subdevice *s,
+				    unsigned int nbytes)
+{
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_write_alloc(s, nbytes);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_write_alloc);
+
+/*
+ * munging is applied to data by core as it passes between user
+ * and kernel space
+ */
+static unsigned int comedi_buf_munge(struct comedi_subdevice *s,
+				     unsigned int num_bytes)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_page *buf_page_list = async->buf_map->page_list;
+	unsigned int count = 0;
+	const unsigned int num_sample_bytes = comedi_bytes_per_sample(s);
+
+	if (!s->munge || (async->cmd.flags & CMDF_RAWDATA) || async->cmd.chanlist_len == 0) {
+		async->munge_count += num_bytes;
+		return num_bytes;
+	}
+
+	/* don't munge partial samples */
+	num_bytes -= num_bytes % num_sample_bytes;
+	while (count < num_bytes) {
+		/*
+		 * Do not munge beyond page boundary.
+		 * Note: prealloc_bufsz is a multiple of PAGE_SIZE.
+		 */
+		unsigned int page = async->munge_ptr >> PAGE_SHIFT;
+		unsigned int offset = offset_in_page(async->munge_ptr);
+		unsigned int block_size =
+			     min(num_bytes - count, PAGE_SIZE - offset);
+
+		s->munge(s->device, s, buf_page_list[page].virt_addr + offset,
+			 block_size, async->munge_chan);
+
+		/*
+		 * ensure data is munged in buffer before the
+		 * async buffer munge_count is incremented
+		 */
+		smp_wmb();
+
+		async->munge_chan += block_size / num_sample_bytes;
+		async->munge_chan %= async->cmd.chanlist_len;
+		async->munge_count += block_size;
+		async->munge_ptr += block_size;
+		if (async->munge_ptr == async->prealloc_bufsz)
+			async->munge_ptr = 0;
+		count += block_size;
+	}
+
+	return count;
+}
+
+unsigned int comedi_buf_write_n_allocated(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+
+	return async->buf_write_alloc_count - async->buf_write_count;
+}
+
+unsigned int _comedi_buf_write_free(struct comedi_subdevice *s,
+				    unsigned int nbytes)
+{
+	struct comedi_async *async = s->async;
+	unsigned int allocated = comedi_buf_write_n_allocated(s);
+
+	if (nbytes > allocated)
+		nbytes = allocated;
+
+	async->buf_write_count += nbytes;
+	async->buf_write_ptr += nbytes;
+	comedi_buf_munge(s, async->buf_write_count - async->munge_count);
+	if (async->buf_write_ptr >= async->prealloc_bufsz)
+		async->buf_write_ptr %= async->prealloc_bufsz;
+
+	return nbytes;
+}
+
+/**
+ * comedi_buf_write_free() - Free buffer space after it is written
+ * @s: COMEDI subdevice.
+ * @nbytes: Maximum space to free in bytes.
+ *
+ * Free up to @nbytes bytes of space previously reserved for writing in the
+ * COMEDI acquisition data buffer associated with the subdevice.  The amount of
+ * space freed is limited to the amount that was reserved.  The freed space is
+ * assumed to have been filled with sample data by the writer.
+ *
+ * If the samples in the freed space need to be "munged", do so here.  The
+ * freed space becomes available for allocation by the reader.
+ *
+ * Return: The amount of space freed in bytes.
+ */
+unsigned int comedi_buf_write_free(struct comedi_subdevice *s,
+				   unsigned int nbytes)
+{
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_write_free(s, nbytes);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_write_free);
+
+unsigned int _comedi_buf_read_n_available(struct comedi_subdevice *s)
+{
+	struct comedi_async *async = s->async;
+	unsigned int num_bytes;
+
+	if (!async)
+		return 0;
+
+	num_bytes = async->munge_count - async->buf_read_count;
+
+	/*
+	 * ensure the async buffer 'counts' are read before we
+	 * attempt to read data from the buffer
+	 */
+	smp_rmb();
+
+	return num_bytes;
+}
+
+/**
+ * comedi_buf_read_n_available() - Determine amount of readable buffer space
+ * @s: COMEDI subdevice.
+ *
+ * Determine the amount of readable buffer space in the COMEDI acquisition data
+ * buffer associated with the subdevice.  The readable buffer space is that
+ * which has been freed by the writer and "munged" to the sample data format
+ * expected by COMEDI if necessary.
+ *
+ * Return: The amount of readable buffer space.
+ */
+unsigned int comedi_buf_read_n_available(struct comedi_subdevice *s)
+{
+	unsigned int num_bytes;
+
+	if (comedi_get_is_subdevice_running(s)) {
+		num_bytes = _comedi_buf_read_n_available(s);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		num_bytes = 0;
+	}
+	return num_bytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_read_n_available);
+
+unsigned int _comedi_buf_read_alloc(struct comedi_subdevice *s,
+				    unsigned int nbytes)
+{
+	struct comedi_async *async = s->async;
+	unsigned int available;
+
+	available = async->munge_count - async->buf_read_alloc_count;
+	if (nbytes > available)
+		nbytes = available;
+
+	async->buf_read_alloc_count += nbytes;
+
+	/*
+	 * ensure the async buffer 'counts' are read before we
+	 * attempt to read data from the read-alloc'ed buffer space
+	 */
+	smp_rmb();
+
+	return nbytes;
+}
+
+/**
+ * comedi_buf_read_alloc() - Reserve buffer space for reading
+ * @s: COMEDI subdevice.
+ * @nbytes: Maximum space to reserve in bytes.
+ *
+ * Reserve up to @nbytes bytes of previously written and "munged" buffer space
+ * for reading in the COMEDI acquisition data buffer associated with the
+ * subdevice.  The amount reserved is limited to the space available.  The
+ * reader can read from the reserved space and then free it.  A reader is also
+ * allowed to read from the space before reserving it as long as it determines
+ * the amount of readable data available, but the space needs to be marked as
+ * reserved before it can be freed.
+ *
+ * Return: The amount of space reserved in bytes.
+ */
+unsigned int comedi_buf_read_alloc(struct comedi_subdevice *s,
+				   unsigned int nbytes)
+{
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_read_alloc(s, nbytes);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_read_alloc);
+
+static unsigned int comedi_buf_read_n_allocated(struct comedi_async *async)
+{
+	return async->buf_read_alloc_count - async->buf_read_count;
+}
+
+unsigned int _comedi_buf_read_free(struct comedi_subdevice *s,
+				   unsigned int nbytes)
+{
+	struct comedi_async *async = s->async;
+	unsigned int allocated;
+
+	/*
+	 * ensure data has been read out of buffer before
+	 * the async read count is incremented
+	 */
+	smp_mb();
+
+	allocated = comedi_buf_read_n_allocated(async);
+	if (nbytes > allocated)
+		nbytes = allocated;
+
+	async->buf_read_count += nbytes;
+	async->buf_read_ptr += nbytes;
+	async->buf_read_ptr %= async->prealloc_bufsz;
+	return nbytes;
+}
+
+/**
+ * comedi_buf_read_free() - Free buffer space after it has been read
+ * @s: COMEDI subdevice.
+ * @nbytes: Maximum space to free in bytes.
+ *
+ * Free up to @nbytes bytes of buffer space previously reserved for reading in
+ * the COMEDI acquisition data buffer associated with the subdevice.  The
+ * amount of space freed is limited to the amount that was reserved.
+ *
+ * The freed space becomes available for allocation by the writer.
+ *
+ * Return: The amount of space freed in bytes.
+ */
+unsigned int comedi_buf_read_free(struct comedi_subdevice *s,
+				  unsigned int nbytes)
+{
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_read_free(s, nbytes);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_read_free);
+
+static void comedi_buf_memcpy_to(struct comedi_subdevice *s,
+				 const void *data, unsigned int num_bytes)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_page *buf_page_list = async->buf_map->page_list;
+	unsigned int write_ptr = async->buf_write_ptr;
+
+	while (num_bytes) {
+		/*
+		 * Do not copy beyond page boundary.
+		 * Note: prealloc_bufsz is a multiple of PAGE_SIZE.
+		 */
+		unsigned int page = write_ptr >> PAGE_SHIFT;
+		unsigned int offset = offset_in_page(write_ptr);
+		unsigned int block_size = min(num_bytes, PAGE_SIZE - offset);
+
+		memcpy(buf_page_list[page].virt_addr + offset,
+		       data, block_size);
+
+		data += block_size;
+		num_bytes -= block_size;
+		write_ptr += block_size;
+		if (write_ptr == async->prealloc_bufsz)
+			write_ptr = 0;
+	}
+}
+
+static void comedi_buf_memcpy_from(struct comedi_subdevice *s,
+				   void *dest, unsigned int nbytes)
+{
+	struct comedi_async *async = s->async;
+	struct comedi_buf_page *buf_page_list = async->buf_map->page_list;
+	unsigned int read_ptr = async->buf_read_ptr;
+
+	while (nbytes) {
+		/*
+		 * Do not copy beyond page boundary.
+		 * Note: prealloc_bufsz is a multiple of PAGE_SIZE.
+		 */
+		unsigned int page = read_ptr >> PAGE_SHIFT;
+		unsigned int offset = offset_in_page(read_ptr);
+		unsigned int block_size = min(nbytes, PAGE_SIZE - offset);
+
+		memcpy(dest, buf_page_list[page].virt_addr + offset,
+		       block_size);
+		nbytes -= block_size;
+		dest += block_size;
+		read_ptr += block_size;
+		if (read_ptr == async->prealloc_bufsz)
+			read_ptr = 0;
+	}
+}
+
+static unsigned int _comedi_buf_write_samples(struct comedi_subdevice *s,
+					      const void *data,
+					      unsigned int nsamples)
+{
+	unsigned int max_samples;
+	unsigned int nbytes;
+
+	/*
+	 * Make sure there is enough room in the buffer for all the samples.
+	 * If not, clamp the nsamples to the number that will fit, flag the
+	 * buffer overrun and add the samples that fit.
+	 */
+	max_samples = comedi_bytes_to_samples(s, comedi_buf_write_n_unalloc(s));
+	if (nsamples > max_samples) {
+		dev_warn(s->device->class_dev, "buffer overrun\n");
+		s->async->events |= COMEDI_CB_OVERFLOW;
+		nsamples = max_samples;
+	}
+
+	if (nsamples == 0)
+		return 0;
+
+	nbytes = comedi_samples_to_bytes(s, nsamples);
+	nbytes = _comedi_buf_write_alloc(s, nbytes);
+	comedi_buf_memcpy_to(s, data, nbytes);
+	_comedi_buf_write_free(s, nbytes);
+	_comedi_inc_scan_progress(s, nbytes);
+	s->async->events |= COMEDI_CB_BLOCK;
+
+	return nbytes;
+}
+
+/**
+ * comedi_buf_write_samples() - Write sample data to COMEDI buffer
+ * @s: COMEDI subdevice.
+ * @data: Pointer to source samples.
+ * @nsamples: Number of samples to write.
+ *
+ * Write up to @nsamples samples to the COMEDI acquisition data buffer
+ * associated with the subdevice, mark it as written and update the
+ * acquisition scan progress.  If there is not enough room for the specified
+ * number of samples, the number of samples written is limited to the number
+ * that will fit and the %COMEDI_CB_OVERFLOW event flag is set to cause the
+ * acquisition to terminate with an overrun error.  Set the %COMEDI_CB_BLOCK
+ * event flag if any samples are written to cause waiting tasks to be woken
+ * when the event flags are processed.
+ *
+ * Return: The amount of data written in bytes.
+ */
+unsigned int comedi_buf_write_samples(struct comedi_subdevice *s,
+				      const void *data, unsigned int nsamples)
+{
+	unsigned int nbytes;
+
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_write_samples(s, data, nsamples);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_write_samples);
+
+static unsigned int _comedi_buf_read_samples(struct comedi_subdevice *s,
+					    void *data, unsigned int nsamples)
+{
+	unsigned int max_samples;
+	unsigned int nbytes;
+
+	/* clamp nsamples to the number of full samples available */
+	max_samples = comedi_bytes_to_samples(s,
+					      _comedi_buf_read_n_available(s));
+	if (nsamples > max_samples)
+		nsamples = max_samples;
+
+	if (nsamples == 0)
+		return 0;
+
+	nbytes = _comedi_buf_read_alloc(s,
+					comedi_samples_to_bytes(s, nsamples));
+	comedi_buf_memcpy_from(s, data, nbytes);
+	_comedi_buf_read_free(s, nbytes);
+	_comedi_inc_scan_progress(s, nbytes);
+	s->async->events |= COMEDI_CB_BLOCK;
+
+	return nbytes;
+}
+
+/**
+ * comedi_buf_read_samples() - Read sample data from COMEDI buffer
+ * @s: COMEDI subdevice.
+ * @data: Pointer to destination.
+ * @nsamples: Maximum number of samples to read.
+ *
+ * Read up to @nsamples samples from the COMEDI acquisition data buffer
+ * associated with the subdevice, mark it as read and update the acquisition
+ * scan progress.  Limit the number of samples read to the number available.
+ * Set the %COMEDI_CB_BLOCK event flag if any samples are read to cause waiting
+ * tasks to be woken when the event flags are processed.
+ *
+ * Return: The amount of data read in bytes.
+ */
+unsigned int comedi_buf_read_samples(struct comedi_subdevice *s,
+				     void *data, unsigned int nsamples)
+{
+	unsigned int nbytes;
+
+	if (comedi_get_is_subdevice_running(s)) {
+		nbytes = _comedi_buf_read_samples(s, data, nsamples);
+		comedi_put_is_subdevice_running(s);
+	} else {
+		nbytes = 0;
+	}
+	return nbytes;
+}
+EXPORT_SYMBOL_GPL(comedi_buf_read_samples);