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, 170 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/funnel-queue.c b/drivers/md/dm-vdo/funnel-queue.c
new file mode 100644
index 000000000..7011963c9
--- /dev/null
+++ b/drivers/md/dm-vdo/funnel-queue.c
@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "funnel-queue.h"
+
+#include "cpu.h"
+#include "memory-alloc.h"
+#include "permassert.h"
+
+int vdo_make_funnel_queue(struct funnel_queue **queue_ptr)
+{
+	int result;
+	struct funnel_queue *queue;
+
+	result = vdo_allocate(1, "funnel queue", &queue);
+	if (result != VDO_SUCCESS)
+		return result;
+
+	/*
+	 * Initialize the stub entry and put it in the queue, establishing the invariant that
+	 * queue->newest and queue->oldest are never null.
+	 */
+	queue->stub.next = NULL;
+	queue->newest = &queue->stub;
+	queue->oldest = &queue->stub;
+
+	*queue_ptr = queue;
+	return VDO_SUCCESS;
+}
+
+void vdo_free_funnel_queue(struct funnel_queue *queue)
+{
+	vdo_free(queue);
+}
+
+static struct funnel_queue_entry *get_oldest(struct funnel_queue *queue)
+{
+	/*
+	 * Barrier requirements: We need a read barrier between reading a "next" field pointer
+	 * value and reading anything it points to. There's an accompanying barrier in
+	 * vdo_funnel_queue_put() between its caller setting up the entry and making it visible.
+	 */
+	struct funnel_queue_entry *oldest = queue->oldest;
+	struct funnel_queue_entry *next = READ_ONCE(oldest->next);
+
+	if (oldest == &queue->stub) {
+		/*
+		 * When the oldest entry is the stub and it has no successor, the queue is
+		 * logically empty.
+		 */
+		if (next == NULL)
+			return NULL;
+		/*
+		 * The stub entry has a successor, so the stub can be dequeued and ignored without
+		 * breaking the queue invariants.
+		 */
+		oldest = next;
+		queue->oldest = oldest;
+		next = READ_ONCE(oldest->next);
+	}
+
+	/*
+	 * We have a non-stub candidate to dequeue. If it lacks a successor, we'll need to put the
+	 * stub entry back on the queue first.
+	 */
+	if (next == NULL) {
+		struct funnel_queue_entry *newest = READ_ONCE(queue->newest);
+
+		if (oldest != newest) {
+			/*
+			 * Another thread has already swung queue->newest atomically, but not yet
+			 * assigned previous->next. The queue is really still empty.
+			 */
+			return NULL;
+		}
+
+		/*
+		 * Put the stub entry back on the queue, ensuring a successor will eventually be
+		 * seen.
+		 */
+		vdo_funnel_queue_put(queue, &queue->stub);
+
+		/* Check again for a successor. */
+		next = READ_ONCE(oldest->next);
+		if (next == NULL) {
+			/*
+			 * We lost a race with a producer who swapped queue->newest before we did,
+			 * but who hasn't yet updated previous->next. Try again later.
+			 */
+			return NULL;
+		}
+	}
+
+	return oldest;
+}
+
+/*
+ * Poll a queue, removing the oldest entry if the queue is not empty. This function must only be
+ * called from a single consumer thread.
+ */
+struct funnel_queue_entry *vdo_funnel_queue_poll(struct funnel_queue *queue)
+{
+	struct funnel_queue_entry *oldest = get_oldest(queue);
+
+	if (oldest == NULL)
+		return oldest;
+
+	/*
+	 * Dequeue the oldest entry and return it. Only one consumer thread may call this function,
+	 * so no locking, atomic operations, or fences are needed; queue->oldest is owned by the
+	 * consumer and oldest->next is never used by a producer thread after it is swung from NULL
+	 * to non-NULL.
+	 */
+	queue->oldest = READ_ONCE(oldest->next);
+	/*
+	 * Make sure the caller sees the proper stored data for this entry. Since we've already
+	 * fetched the entry pointer we stored in "queue->oldest", this also ensures that on entry
+	 * to the next call we'll properly see the dependent data.
+	 */
+	smp_rmb();
+	/*
+	 * If "oldest" is a very light-weight work item, we'll be looking for the next one very
+	 * soon, so prefetch it now.
+	 */
+	uds_prefetch_address(queue->oldest, true);
+	WRITE_ONCE(oldest->next, NULL);
+	return oldest;
+}
+
+/*
+ * Check whether the funnel queue is empty or not. If the queue is in a transition state with one
+ * or more entries being added such that the list view is incomplete, this function will report the
+ * queue as empty.
+ */
+bool vdo_is_funnel_queue_empty(struct funnel_queue *queue)
+{
+	return get_oldest(queue) == NULL;
+}
+
+/*
+ * Check whether the funnel queue is idle or not. If the queue has entries available to be
+ * retrieved, it is not idle. If the queue is in a transition state with one or more entries being
+ * added such that the list view is incomplete, it may not be possible to retrieve an entry with
+ * the vdo_funnel_queue_poll() function, but the queue will not be considered idle.
+ */
+bool vdo_is_funnel_queue_idle(struct funnel_queue *queue)
+{
+	/*
+	 * Oldest is not the stub, so there's another entry, though if next is NULL we can't
+	 * retrieve it yet.
+	 */
+	if (queue->oldest != &queue->stub)
+		return false;
+
+	/*
+	 * Oldest is the stub, but newest has been updated by _put(); either there's another,
+	 * retrievable entry in the list, or the list is officially empty but in the intermediate
+	 * state of having an entry added.
+	 *
+	 * Whether anything is retrievable depends on whether stub.next has been updated and become
+	 * visible to us, but for idleness we don't care. And due to memory ordering in _put(), the
+	 * update to newest would be visible to us at the same time or sooner.
+	 */
+	if (READ_ONCE(queue->newest) != &queue->stub)
+		return false;
+
+	return true;
+}