Merge tag 'for-6.9/dm-vdo' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper VDO target from Mike Snitzer:
 "Introduce the DM vdo target which provides block-level deduplication,
  compression, and thin provisioning. Please see:

      Documentation/admin-guide/device-mapper/vdo.rst
      Documentation/admin-guide/device-mapper/vdo-design.rst

  The DM vdo target handles its concurrency by pinning an IO, and
  subsequent stages of handling that IO, to a particular VDO thread.
  This aspect of VDO is "unique" but its overall implementation is very
  tightly coupled to its mostly lockless threading model. As such, VDO
  is not easily changed to use more traditional finer-grained locking
  and Linux workqueues. Please see the "Zones and Threading" section of
  vdo-design.rst

  The DM vdo target has been used in production for many years but has
  seen significant changes over the past ~6 years to prepare it for
  upstream inclusion. The codebase is still large but it is isolated to
  drivers/md/dm-vdo/ and has been made considerably more approachable
  and maintainable.

  Matt Sakai has been added to the MAINTAINERS file to reflect that he
  will send VDO changes upstream through the DM subsystem maintainers"

* tag 'for-6.9/dm-vdo' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: (142 commits)
  dm vdo: document minimum metadata size requirements
  dm vdo: remove meaningless version number constant
  dm vdo: remove vdo_perform_once
  dm vdo block-map: Remove stray semicolon
  dm vdo string-utils: change from uds_ to vdo_ namespace
  dm vdo logger: change from uds_ to vdo_ namespace
  dm vdo funnel-queue: change from uds_ to vdo_ namespace
  dm vdo indexer: fix use after free
  dm vdo logger: remove log level to string conversion code
  dm vdo: document log_level parameter
  dm vdo: add 'log_level' module parameter
  dm vdo: remove all sysfs interfaces
  dm vdo target: eliminate inappropriate uses of UDS_SUCCESS
  dm vdo indexer: update ASSERT and ASSERT_LOG_ONLY usage
  dm vdo encodings: update some stale comments
  dm vdo permassert: audit all of ASSERT to test for VDO_SUCCESS
  dm-vdo funnel-workqueue: return VDO_SUCCESS from make_simple_work_queue
  dm vdo thread-utils: return VDO_SUCCESS on vdo_create_thread success
  dm vdo int-map: return VDO_SUCCESS on success
  dm vdo: check for VDO_SUCCESS return value from memory-alloc functions
  ...

1 files changed, 110 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/funnel-queue.h b/drivers/md/dm-vdo/funnel-queue.h
new file mode 100644
index 000000000000..bde0f1deff98
--- /dev/null
+++ b/drivers/md/dm-vdo/funnel-queue.h
@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef VDO_FUNNEL_QUEUE_H
+#define VDO_FUNNEL_QUEUE_H
+
+#include <linux/atomic.h>
+#include <linux/cache.h>
+
+/*
+ * A funnel queue is a simple (almost) lock-free queue that accepts entries from multiple threads
+ * (multi-producer) and delivers them to a single thread (single-consumer). "Funnel" is an attempt
+ * to evoke the image of requests from more than one producer being "funneled down" to a single
+ * consumer.
+ *
+ * This is an unsynchronized but thread-safe data structure when used as intended. There is no
+ * mechanism to ensure that only one thread is consuming from the queue. If more than one thread
+ * attempts to consume from the queue, the resulting behavior is undefined. Clients must not
+ * directly access or manipulate the internals of the queue, which are only exposed for the purpose
+ * of allowing the very simple enqueue operation to be inlined.
+ *
+ * The implementation requires that a funnel_queue_entry structure (a link pointer) is embedded in
+ * the queue entries, and pointers to those structures are used exclusively by the queue. No macros
+ * are defined to template the queue, so the offset of the funnel_queue_entry in the records placed
+ * in the queue must all be the same so the client can derive their structure pointer from the
+ * entry pointer returned by vdo_funnel_queue_poll().
+ *
+ * Callers are wholly responsible for allocating and freeing the entries. Entries may be freed as
+ * soon as they are returned since this queue is not susceptible to the "ABA problem" present in
+ * many lock-free data structures. The queue is dynamically allocated to ensure cache-line
+ * alignment, but no other dynamic allocation is used.
+ *
+ * The algorithm is not actually 100% lock-free. There is a single point in vdo_funnel_queue_put()
+ * at which a preempted producer will prevent the consumers from seeing items added to the queue by
+ * later producers, and only if the queue is short enough or the consumer fast enough for it to
+ * reach what was the end of the queue at the time of the preemption.
+ *
+ * The consumer function, vdo_funnel_queue_poll(), will return NULL when the queue is empty. To
+ * wait for data to consume, spin (if safe) or combine the queue with a struct event_count to
+ * signal the presence of new entries.
+ */
+
+/* This queue link structure must be embedded in client entries. */
+struct funnel_queue_entry {
+	/* The next (newer) entry in the queue. */
+	struct funnel_queue_entry *next;
+};
+
+/*
+ * The dynamically allocated queue structure, which is allocated on a cache line boundary so the
+ * producer and consumer fields in the structure will land on separate cache lines. This should be
+ * consider opaque but it is exposed here so vdo_funnel_queue_put() can be inlined.
+ */
+struct __aligned(L1_CACHE_BYTES) funnel_queue {
+	/*
+	 * The producers' end of the queue, an atomically exchanged pointer that will never be
+	 * NULL.
+	 */
+	struct funnel_queue_entry *newest;
+
+	/* The consumer's end of the queue, which is owned by the consumer and never NULL. */
+	struct funnel_queue_entry *oldest __aligned(L1_CACHE_BYTES);
+
+	/* A dummy entry used to provide the non-NULL invariants above. */
+	struct funnel_queue_entry stub;
+};
+
+int __must_check vdo_make_funnel_queue(struct funnel_queue **queue_ptr);
+
+void vdo_free_funnel_queue(struct funnel_queue *queue);
+
+/*
+ * Put an entry on the end of the queue.
+ *
+ * The entry pointer must be to the struct funnel_queue_entry embedded in the caller's data
+ * structure. The caller must be able to derive the address of the start of their data structure
+ * from the pointer that passed in here, so every entry in the queue must have the struct
+ * funnel_queue_entry at the same offset within the client's structure.
+ */
+static inline void vdo_funnel_queue_put(struct funnel_queue *queue,
+					struct funnel_queue_entry *entry)
+{
+	struct funnel_queue_entry *previous;
+
+	/*
+	 * Barrier requirements: All stores relating to the entry ("next" pointer, containing data
+	 * structure fields) must happen before the previous->next store making it visible to the
+	 * consumer. Also, the entry's "next" field initialization to NULL must happen before any
+	 * other producer threads can see the entry (the xchg) and try to update the "next" field.
+	 *
+	 * xchg implements a full barrier.
+	 */
+	WRITE_ONCE(entry->next, NULL);
+	previous = xchg(&queue->newest, entry);
+	/*
+	 * Preemptions between these two statements hide the rest of the queue from the consumer,
+	 * preventing consumption until the following assignment runs.
+	 */
+	WRITE_ONCE(previous->next, entry);
+}
+
+struct funnel_queue_entry *__must_check vdo_funnel_queue_poll(struct funnel_queue *queue);
+
+bool __must_check vdo_is_funnel_queue_empty(struct funnel_queue *queue);
+
+bool __must_check vdo_is_funnel_queue_idle(struct funnel_queue *queue);
+
+#endif /* VDO_FUNNEL_QUEUE_H */