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, 878 insertions, 0 deletions

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
new file mode 100644
index 000000000..dd2717ff9
--- /dev/null
+++ b/lib/stackdepot.c
@@ -0,0 +1,878 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Stack depot - a stack trace storage that avoids duplication.
+ *
+ * Internally, stack depot maintains a hash table of unique stacktraces. The
+ * stack traces themselves are stored contiguously one after another in a set
+ * of separate page allocations.
+ *
+ * Author: Alexander Potapenko <glider@google.com>
+ * Copyright (C) 2016 Google, Inc.
+ *
+ * Based on the code by Dmitry Chernenkov.
+ */
+
+#define pr_fmt(fmt) "stackdepot: " fmt
+
+#include <linux/debugfs.h>
+#include <linux/gfp.h>
+#include <linux/jhash.h>
+#include <linux/kernel.h>
+#include <linux/kmsan.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+#include <linux/poison.h>
+#include <linux/printk.h>
+#include <linux/rculist.h>
+#include <linux/rcupdate.h>
+#include <linux/refcount.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/stacktrace.h>
+#include <linux/stackdepot.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/memblock.h>
+#include <linux/kasan-enabled.h>
+
+/*
+ * The pool_index is offset by 1 so the first record does not have a 0 handle.
+ */
+static unsigned int stack_max_pools __read_mostly =
+	MIN((1LL << DEPOT_POOL_INDEX_BITS) - 1, 8192);
+
+static bool stack_depot_disabled;
+static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
+static bool __stack_depot_early_init_passed __initdata;
+
+/* Use one hash table bucket per 16 KB of memory. */
+#define STACK_HASH_TABLE_SCALE 14
+/* Limit the number of buckets between 4K and 1M. */
+#define STACK_BUCKET_NUMBER_ORDER_MIN 12
+#define STACK_BUCKET_NUMBER_ORDER_MAX 20
+/* Initial seed for jhash2. */
+#define STACK_HASH_SEED 0x9747b28c
+
+/* Hash table of stored stack records. */
+static struct list_head *stack_table;
+/* Fixed order of the number of table buckets. Used when KASAN is enabled. */
+static unsigned int stack_bucket_number_order;
+/* Hash mask for indexing the table. */
+static unsigned int stack_hash_mask;
+
+/* The lock must be held when performing pool or freelist modifications. */
+static DEFINE_RAW_SPINLOCK(pool_lock);
+/* Array of memory regions that store stack records. */
+static void **stack_pools __pt_guarded_by(&pool_lock);
+/* Newly allocated pool that is not yet added to stack_pools. */
+static void *new_pool;
+/* Number of pools in stack_pools. */
+static int pools_num;
+/* Offset to the unused space in the currently used pool. */
+static size_t pool_offset __guarded_by(&pool_lock) = DEPOT_POOL_SIZE;
+/* Freelist of stack records within stack_pools. */
+static __guarded_by(&pool_lock) LIST_HEAD(free_stacks);
+
+/* Statistics counters for debugfs. */
+enum depot_counter_id {
+	DEPOT_COUNTER_REFD_ALLOCS,
+	DEPOT_COUNTER_REFD_FREES,
+	DEPOT_COUNTER_REFD_INUSE,
+	DEPOT_COUNTER_FREELIST_SIZE,
+	DEPOT_COUNTER_PERSIST_COUNT,
+	DEPOT_COUNTER_PERSIST_BYTES,
+	DEPOT_COUNTER_COUNT,
+};
+static long counters[DEPOT_COUNTER_COUNT];
+static const char *const counter_names[] = {
+	[DEPOT_COUNTER_REFD_ALLOCS]	= "refcounted_allocations",
+	[DEPOT_COUNTER_REFD_FREES]	= "refcounted_frees",
+	[DEPOT_COUNTER_REFD_INUSE]	= "refcounted_in_use",
+	[DEPOT_COUNTER_FREELIST_SIZE]	= "freelist_size",
+	[DEPOT_COUNTER_PERSIST_COUNT]	= "persistent_count",
+	[DEPOT_COUNTER_PERSIST_BYTES]	= "persistent_bytes",
+};
+static_assert(ARRAY_SIZE(counter_names) == DEPOT_COUNTER_COUNT);
+
+static int __init disable_stack_depot(char *str)
+{
+	return kstrtobool(str, &stack_depot_disabled);
+}
+early_param("stack_depot_disable", disable_stack_depot);
+
+static int __init parse_max_pools(char *str)
+{
+	const long long limit = (1LL << (DEPOT_POOL_INDEX_BITS)) - 1;
+	unsigned int max_pools;
+	int rv;
+
+	rv = kstrtouint(str, 0, &max_pools);
+	if (rv)
+		return rv;
+
+	if (max_pools < 1024) {
+		pr_err("stack_depot_max_pools below 1024, using default of %u\n",
+		       stack_max_pools);
+		goto out;
+	}
+
+	if (max_pools > limit) {
+		pr_err("stack_depot_max_pools exceeds %lld, using default of %u\n",
+		       limit, stack_max_pools);
+		goto out;
+	}
+
+	stack_max_pools = max_pools;
+out:
+	return 0;
+}
+early_param("stack_depot_max_pools", parse_max_pools);
+
+void __init stack_depot_request_early_init(void)
+{
+	/* Too late to request early init now. */
+	WARN_ON(__stack_depot_early_init_passed);
+
+	__stack_depot_early_init_requested = true;
+}
+
+/* Initialize list_head's within the hash table. */
+static void init_stack_table(unsigned long entries)
+{
+	unsigned long i;
+
+	for (i = 0; i < entries; i++)
+		INIT_LIST_HEAD(&stack_table[i]);
+}
+
+/* Allocates a hash table via memblock. Can only be used during early boot. */
+int __init stack_depot_early_init(void)
+{
+	unsigned long entries = 0;
+
+	/* This function must be called only once, from mm_init(). */
+	if (WARN_ON(__stack_depot_early_init_passed))
+		return 0;
+	__stack_depot_early_init_passed = true;
+
+	/*
+	 * Print disabled message even if early init has not been requested:
+	 * stack_depot_init() will not print one.
+	 */
+	if (stack_depot_disabled) {
+		pr_info("disabled\n");
+		return 0;
+	}
+
+	/*
+	 * If KASAN is enabled, use the maximum order: KASAN is frequently used
+	 * in fuzzing scenarios, which leads to a large number of different
+	 * stack traces being stored in stack depot.
+	 */
+	if (kasan_enabled() && !stack_bucket_number_order)
+		stack_bucket_number_order = STACK_BUCKET_NUMBER_ORDER_MAX;
+
+	/*
+	 * Check if early init has been requested after setting
+	 * stack_bucket_number_order: stack_depot_init() uses its value.
+	 */
+	if (!__stack_depot_early_init_requested)
+		return 0;
+
+	/*
+	 * If stack_bucket_number_order is not set, leave entries as 0 to rely
+	 * on the automatic calculations performed by alloc_large_system_hash().
+	 */
+	if (stack_bucket_number_order)
+		entries = 1UL << stack_bucket_number_order;
+	pr_info("allocating hash table via alloc_large_system_hash\n");
+	stack_table = alloc_large_system_hash("stackdepot",
+						sizeof(struct list_head),
+						entries,
+						STACK_HASH_TABLE_SCALE,
+						HASH_EARLY,
+						NULL,
+						&stack_hash_mask,
+						1UL << STACK_BUCKET_NUMBER_ORDER_MIN,
+						1UL << STACK_BUCKET_NUMBER_ORDER_MAX);
+	if (!stack_table) {
+		pr_err("hash table allocation failed, disabling\n");
+		stack_depot_disabled = true;
+		return -ENOMEM;
+	}
+	if (!entries) {
+		/*
+		 * Obtain the number of entries that was calculated by
+		 * alloc_large_system_hash().
+		 */
+		entries = stack_hash_mask + 1;
+	}
+	init_stack_table(entries);
+
+	pr_info("allocating space for %u stack pools via memblock\n",
+		stack_max_pools);
+	stack_pools =
+		memblock_alloc(stack_max_pools * sizeof(void *), PAGE_SIZE);
+	if (!stack_pools) {
+		pr_err("stack pools allocation failed, disabling\n");
+		memblock_free(stack_table, entries * sizeof(struct list_head));
+		stack_depot_disabled = true;
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+/* Allocates a hash table via kvcalloc. Can be used after boot. */
+int stack_depot_init(void)
+{
+	static DEFINE_MUTEX(stack_depot_init_mutex);
+	unsigned long entries;
+	int ret = 0;
+
+	mutex_lock(&stack_depot_init_mutex);
+
+	if (stack_depot_disabled || stack_table)
+		goto out_unlock;
+
+	/*
+	 * Similarly to stack_depot_early_init, use stack_bucket_number_order
+	 * if assigned, and rely on automatic scaling otherwise.
+	 */
+	if (stack_bucket_number_order) {
+		entries = 1UL << stack_bucket_number_order;
+	} else {
+		int scale = STACK_HASH_TABLE_SCALE;
+
+		entries = nr_free_buffer_pages();
+		entries = roundup_pow_of_two(entries);
+
+		if (scale > PAGE_SHIFT)
+			entries >>= (scale - PAGE_SHIFT);
+		else
+			entries <<= (PAGE_SHIFT - scale);
+	}
+
+	if (entries < 1UL << STACK_BUCKET_NUMBER_ORDER_MIN)
+		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MIN;
+	if (entries > 1UL << STACK_BUCKET_NUMBER_ORDER_MAX)
+		entries = 1UL << STACK_BUCKET_NUMBER_ORDER_MAX;
+
+	pr_info("allocating hash table of %lu entries via kvcalloc\n", entries);
+	stack_table = kvzalloc_objs(struct list_head, entries);
+	if (!stack_table) {
+		pr_err("hash table allocation failed, disabling\n");
+		stack_depot_disabled = true;
+		ret = -ENOMEM;
+		goto out_unlock;
+	}
+	stack_hash_mask = entries - 1;
+	init_stack_table(entries);
+
+	pr_info("allocating space for %u stack pools via kvcalloc\n",
+		stack_max_pools);
+	stack_pools = kvcalloc(stack_max_pools, sizeof(void *), GFP_KERNEL);
+	if (!stack_pools) {
+		pr_err("stack pools allocation failed, disabling\n");
+		kvfree(stack_table);
+		stack_depot_disabled = true;
+		ret = -ENOMEM;
+	}
+
+out_unlock:
+	mutex_unlock(&stack_depot_init_mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(stack_depot_init);
+
+/*
+ * Initializes new stack pool, and updates the list of pools.
+ */
+static bool depot_init_pool(void **prealloc)
+	__must_hold(&pool_lock)
+{
+	lockdep_assert_held(&pool_lock);
+
+	if (unlikely(pools_num >= stack_max_pools)) {
+		/* Bail out if we reached the pool limit. */
+		WARN_ON_ONCE(pools_num > stack_max_pools); /* should never happen */
+		WARN_ON_ONCE(!new_pool); /* to avoid unnecessary pre-allocation */
+		WARN_ONCE(1, "Stack depot reached limit capacity");
+		return false;
+	}
+
+	if (!new_pool && *prealloc) {
+		/* We have preallocated memory, use it. */
+		WRITE_ONCE(new_pool, *prealloc);
+		*prealloc = NULL;
+	}
+
+	if (!new_pool)
+		return false; /* new_pool and *prealloc are NULL */
+
+	/* Save reference to the pool to be used by depot_fetch_stack(). */
+	stack_pools[pools_num] = new_pool;
+
+	/*
+	 * Stack depot tries to keep an extra pool allocated even before it runs
+	 * out of space in the currently used pool.
+	 *
+	 * To indicate that a new preallocation is needed new_pool is reset to
+	 * NULL; do not reset to NULL if we have reached the maximum number of
+	 * pools.
+	 */
+	if (pools_num < stack_max_pools)
+		WRITE_ONCE(new_pool, NULL);
+	else
+		WRITE_ONCE(new_pool, STACK_DEPOT_POISON);
+
+	/* Pairs with concurrent READ_ONCE() in depot_fetch_stack(). */
+	WRITE_ONCE(pools_num, pools_num + 1);
+	ASSERT_EXCLUSIVE_WRITER(pools_num);
+
+	pool_offset = 0;
+
+	return true;
+}
+
+/* Keeps the preallocated memory to be used for a new stack depot pool. */
+static void depot_keep_new_pool(void **prealloc)
+	__must_hold(&pool_lock)
+{
+	lockdep_assert_held(&pool_lock);
+
+	/*
+	 * If a new pool is already saved or the maximum number of
+	 * pools is reached, do not use the preallocated memory.
+	 */
+	if (new_pool)
+		return;
+
+	WRITE_ONCE(new_pool, *prealloc);
+	*prealloc = NULL;
+}
+
+/*
+ * Try to initialize a new stack record from the current pool, a cached pool, or
+ * the current pre-allocation.
+ */
+static struct stack_record *depot_pop_free_pool(void **prealloc, size_t size)
+	__must_hold(&pool_lock)
+{
+	struct stack_record *stack;
+	void *current_pool;
+	u32 pool_index;
+
+	lockdep_assert_held(&pool_lock);
+
+	if (pool_offset + size > DEPOT_POOL_SIZE) {
+		if (!depot_init_pool(prealloc))
+			return NULL;
+	}
+
+	if (WARN_ON_ONCE(pools_num < 1))
+		return NULL;
+	pool_index = pools_num - 1;
+	current_pool = stack_pools[pool_index];
+	if (WARN_ON_ONCE(!current_pool))
+		return NULL;
+
+	stack = current_pool + pool_offset;
+
+	/* Pre-initialize handle once. */
+	stack->handle.pool_index_plus_1 = pool_index + 1;
+	stack->handle.offset = pool_offset >> DEPOT_STACK_ALIGN;
+	stack->handle.extra = 0;
+	INIT_LIST_HEAD(&stack->hash_list);
+
+	pool_offset += size;
+
+	return stack;
+}
+
+/* Try to find next free usable entry from the freelist. */
+static struct stack_record *depot_pop_free(void)
+	__must_hold(&pool_lock)
+{
+	struct stack_record *stack;
+
+	lockdep_assert_held(&pool_lock);
+
+	if (list_empty(&free_stacks))
+		return NULL;
+
+	/*
+	 * We maintain the invariant that the elements in front are least
+	 * recently used, and are therefore more likely to be associated with an
+	 * RCU grace period in the past. Consequently it is sufficient to only
+	 * check the first entry.
+	 */
+	stack = list_first_entry(&free_stacks, struct stack_record, free_list);
+	if (!poll_state_synchronize_rcu(stack->rcu_state))
+		return NULL;
+
+	list_del(&stack->free_list);
+	counters[DEPOT_COUNTER_FREELIST_SIZE]--;
+
+	return stack;
+}
+
+static inline size_t depot_stack_record_size(struct stack_record *s, unsigned int nr_entries)
+{
+	const size_t used = flex_array_size(s, entries, nr_entries);
+	const size_t unused = sizeof(s->entries) - used;
+
+	WARN_ON_ONCE(sizeof(s->entries) < used);
+
+	return ALIGN(sizeof(struct stack_record) - unused, 1 << DEPOT_STACK_ALIGN);
+}
+
+/* Allocates a new stack in a stack depot pool. */
+static struct stack_record *
+depot_alloc_stack(unsigned long *entries, unsigned int nr_entries, u32 hash, depot_flags_t flags, void **prealloc)
+	__must_hold(&pool_lock)
+{
+	struct stack_record *stack = NULL;
+	size_t record_size;
+
+	lockdep_assert_held(&pool_lock);
+
+	/* This should already be checked by public API entry points. */
+	if (WARN_ON_ONCE(!nr_entries))
+		return NULL;
+
+	/* Limit number of saved frames to CONFIG_STACKDEPOT_MAX_FRAMES. */
+	if (nr_entries > CONFIG_STACKDEPOT_MAX_FRAMES)
+		nr_entries = CONFIG_STACKDEPOT_MAX_FRAMES;
+
+	if (flags & STACK_DEPOT_FLAG_GET) {
+		/*
+		 * Evictable entries have to allocate the max. size so they may
+		 * safely be re-used by differently sized allocations.
+		 */
+		record_size = depot_stack_record_size(stack, CONFIG_STACKDEPOT_MAX_FRAMES);
+		stack = depot_pop_free();
+	} else {
+		record_size = depot_stack_record_size(stack, nr_entries);
+	}
+
+	if (!stack) {
+		stack = depot_pop_free_pool(prealloc, record_size);
+		if (!stack)
+			return NULL;
+	}
+
+	/* Save the stack trace. */
+	stack->hash = hash;
+	stack->size = nr_entries;
+	/* stack->handle is already filled in by depot_pop_free_pool(). */
+	memcpy(stack->entries, entries, flex_array_size(stack, entries, nr_entries));
+
+	if (flags & STACK_DEPOT_FLAG_GET) {
+		refcount_set(&stack->count, 1);
+		counters[DEPOT_COUNTER_REFD_ALLOCS]++;
+		counters[DEPOT_COUNTER_REFD_INUSE]++;
+	} else {
+		/* Warn on attempts to switch to refcounting this entry. */
+		refcount_set(&stack->count, REFCOUNT_SATURATED);
+		counters[DEPOT_COUNTER_PERSIST_COUNT]++;
+		counters[DEPOT_COUNTER_PERSIST_BYTES] += record_size;
+	}
+
+	/*
+	 * Let KMSAN know the stored stack record is initialized. This shall
+	 * prevent false positive reports if instrumented code accesses it.
+	 */
+	kmsan_unpoison_memory(stack, record_size);
+
+	return stack;
+}
+
+static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
+	__must_not_hold(&pool_lock)
+{
+	const int pools_num_cached = READ_ONCE(pools_num);
+	union handle_parts parts = { .handle = handle };
+	void *pool;
+	u32 pool_index = parts.pool_index_plus_1 - 1;
+	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
+	struct stack_record *stack;
+
+	lockdep_assert_not_held(&pool_lock);
+
+	if (pool_index >= pools_num_cached) {
+		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
+		     pool_index, pools_num_cached, handle);
+		return NULL;
+	}
+
+	/* @pool_index either valid, or user passed in corrupted value. */
+	pool = context_unsafe(stack_pools[pool_index]);
+	if (WARN_ON(!pool))
+		return NULL;
+
+	stack = pool + offset;
+	if (WARN_ON(!refcount_read(&stack->count)))
+		return NULL;
+
+	return stack;
+}
+
+/* Links stack into the freelist. */
+static void depot_free_stack(struct stack_record *stack)
+	__must_not_hold(&pool_lock)
+{
+	unsigned long flags;
+
+	lockdep_assert_not_held(&pool_lock);
+
+	raw_spin_lock_irqsave(&pool_lock, flags);
+	printk_deferred_enter();
+
+	/*
+	 * Remove the entry from the hash list. Concurrent list traversal may
+	 * still observe the entry, but since the refcount is zero, this entry
+	 * will no longer be considered as valid.
+	 */
+	list_del_rcu(&stack->hash_list);
+
+	/*
+	 * Due to being used from constrained contexts such as the allocators,
+	 * NMI, or even RCU itself, stack depot cannot rely on primitives that
+	 * would sleep (such as synchronize_rcu()) or recursively call into
+	 * stack depot again (such as call_rcu()).
+	 *
+	 * Instead, get an RCU cookie, so that we can ensure this entry isn't
+	 * moved onto another list until the next grace period, and concurrent
+	 * RCU list traversal remains safe.
+	 */
+	stack->rcu_state = get_state_synchronize_rcu();
+
+	/*
+	 * Add the entry to the freelist tail, so that older entries are
+	 * considered first - their RCU cookie is more likely to no longer be
+	 * associated with the current grace period.
+	 */
+	list_add_tail(&stack->free_list, &free_stacks);
+
+	counters[DEPOT_COUNTER_FREELIST_SIZE]++;
+	counters[DEPOT_COUNTER_REFD_FREES]++;
+	counters[DEPOT_COUNTER_REFD_INUSE]--;
+
+	printk_deferred_exit();
+	raw_spin_unlock_irqrestore(&pool_lock, flags);
+}
+
+/* Calculates the hash for a stack. */
+static inline u32 hash_stack(unsigned long *entries, unsigned int size)
+{
+	return jhash2((u32 *)entries,
+		      array_size(size,  sizeof(*entries)) / sizeof(u32),
+		      STACK_HASH_SEED);
+}
+
+/*
+ * Non-instrumented version of memcmp().
+ * Does not check the lexicographical order, only the equality.
+ */
+static inline
+int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2,
+			unsigned int n)
+{
+	for ( ; n-- ; u1++, u2++) {
+		if (*u1 != *u2)
+			return 1;
+	}
+	return 0;
+}
+
+/* Finds a stack in a bucket of the hash table. */
+static inline struct stack_record *find_stack(struct list_head *bucket,
+					      unsigned long *entries, int size,
+					      u32 hash, depot_flags_t flags)
+{
+	struct stack_record *stack, *ret = NULL;
+
+	/*
+	 * Stack depot may be used from instrumentation that instruments RCU or
+	 * tracing itself; use variant that does not call into RCU and cannot be
+	 * traced.
+	 *
+	 * Note: Such use cases must take care when using refcounting to evict
+	 * unused entries, because the stack record free-then-reuse code paths
+	 * do call into RCU.
+	 */
+	rcu_read_lock_sched_notrace();
+
+	list_for_each_entry_rcu(stack, bucket, hash_list) {
+		if (stack->hash != hash || stack->size != size)
+			continue;
+
+		/*
+		 * This may race with depot_free_stack() accessing the freelist
+		 * management state unioned with @entries. The refcount is zero
+		 * in that case and the below refcount_inc_not_zero() will fail.
+		 */
+		if (data_race(stackdepot_memcmp(entries, stack->entries, size)))
+			continue;
+
+		/*
+		 * Try to increment refcount. If this succeeds, the stack record
+		 * is valid and has not yet been freed.
+		 *
+		 * If STACK_DEPOT_FLAG_GET is not used, it is undefined behavior
+		 * to then call stack_depot_put() later, and we can assume that
+		 * a stack record is never placed back on the freelist.
+		 */
+		if ((flags & STACK_DEPOT_FLAG_GET) && !refcount_inc_not_zero(&stack->count))
+			continue;
+
+		ret = stack;
+		break;
+	}
+
+	rcu_read_unlock_sched_notrace();
+
+	return ret;
+}
+
+depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
+					    unsigned int nr_entries,
+					    gfp_t alloc_flags,
+					    depot_flags_t depot_flags)
+{
+	struct list_head *bucket;
+	struct stack_record *found = NULL;
+	depot_stack_handle_t handle = 0;
+	struct page *page = NULL;
+	void *prealloc = NULL;
+	bool allow_spin = gfpflags_allow_spinning(alloc_flags);
+	bool can_alloc = (depot_flags & STACK_DEPOT_FLAG_CAN_ALLOC) && allow_spin;
+	unsigned long flags;
+	u32 hash;
+
+	if (WARN_ON(depot_flags & ~STACK_DEPOT_FLAGS_MASK))
+		return 0;
+
+	/*
+	 * If this stack trace is from an interrupt, including anything before
+	 * interrupt entry usually leads to unbounded stack depot growth.
+	 *
+	 * Since use of filter_irq_stacks() is a requirement to ensure stack
+	 * depot can efficiently deduplicate interrupt stacks, always
+	 * filter_irq_stacks() to simplify all callers' use of stack depot.
+	 */
+	nr_entries = filter_irq_stacks(entries, nr_entries);
+
+	if (unlikely(nr_entries == 0) || stack_depot_disabled)
+		return 0;
+
+	hash = hash_stack(entries, nr_entries);
+	bucket = &stack_table[hash & stack_hash_mask];
+
+	/* Fast path: look the stack trace up without locking. */
+	found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
+	if (found)
+		goto exit;
+
+	/*
+	 * Allocate memory for a new pool if required now:
+	 * we won't be able to do that under the lock.
+	 */
+	if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
+		page = alloc_pages(gfp_nested_mask(alloc_flags),
+				   DEPOT_POOL_ORDER);
+		if (page)
+			prealloc = page_address(page);
+	}
+
+	if (in_nmi() || !allow_spin) {
+		/* We can never allocate in NMI context. */
+		WARN_ON_ONCE(can_alloc);
+		/* Best effort; bail if we fail to take the lock. */
+		if (!raw_spin_trylock_irqsave(&pool_lock, flags))
+			goto exit;
+	} else {
+		raw_spin_lock_irqsave(&pool_lock, flags);
+	}
+	printk_deferred_enter();
+
+	/* Try to find again, to avoid concurrently inserting duplicates. */
+	found = find_stack(bucket, entries, nr_entries, hash, depot_flags);
+	if (!found) {
+		struct stack_record *new =
+			depot_alloc_stack(entries, nr_entries, hash, depot_flags, &prealloc);
+
+		if (new) {
+			/*
+			 * This releases the stack record into the bucket and
+			 * makes it visible to readers in find_stack().
+			 */
+			list_add_rcu(&new->hash_list, bucket);
+			found = new;
+		}
+	}
+
+	if (prealloc) {
+		/*
+		 * Either stack depot already contains this stack trace, or
+		 * depot_alloc_stack() did not consume the preallocated memory.
+		 * Try to keep the preallocated memory for future.
+		 */
+		depot_keep_new_pool(&prealloc);
+	}
+
+	printk_deferred_exit();
+	raw_spin_unlock_irqrestore(&pool_lock, flags);
+exit:
+	if (prealloc) {
+		/* Stack depot didn't use this memory, free it. */
+		if (!allow_spin)
+			free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER);
+		else
+			free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
+	}
+	if (found)
+		handle = found->handle.handle;
+	return handle;
+}
+EXPORT_SYMBOL_GPL(stack_depot_save_flags);
+
+depot_stack_handle_t stack_depot_save(unsigned long *entries,
+				      unsigned int nr_entries,
+				      gfp_t alloc_flags)
+{
+	return stack_depot_save_flags(entries, nr_entries, alloc_flags,
+				      STACK_DEPOT_FLAG_CAN_ALLOC);
+}
+EXPORT_SYMBOL_GPL(stack_depot_save);
+
+struct stack_record *__stack_depot_get_stack_record(depot_stack_handle_t handle)
+{
+	if (!handle)
+		return NULL;
+
+	return depot_fetch_stack(handle);
+}
+
+unsigned int stack_depot_fetch(depot_stack_handle_t handle,
+			       unsigned long **entries)
+{
+	struct stack_record *stack;
+
+	*entries = NULL;
+	/*
+	 * Let KMSAN know *entries is initialized. This shall prevent false
+	 * positive reports if instrumented code accesses it.
+	 */
+	kmsan_unpoison_memory(entries, sizeof(*entries));
+
+	if (!handle || stack_depot_disabled)
+		return 0;
+
+	stack = depot_fetch_stack(handle);
+	/*
+	 * Should never be NULL, otherwise this is a use-after-put (or just a
+	 * corrupt handle).
+	 */
+	if (WARN(!stack, "corrupt handle or use after stack_depot_put()"))
+		return 0;
+
+	*entries = stack->entries;
+	return stack->size;
+}
+EXPORT_SYMBOL_GPL(stack_depot_fetch);
+
+void stack_depot_put(depot_stack_handle_t handle)
+{
+	struct stack_record *stack;
+
+	if (!handle || stack_depot_disabled)
+		return;
+
+	stack = depot_fetch_stack(handle);
+	/*
+	 * Should always be able to find the stack record, otherwise this is an
+	 * unbalanced put attempt (or corrupt handle).
+	 */
+	if (WARN(!stack, "corrupt handle or unbalanced stack_depot_put()"))
+		return;
+
+	if (refcount_dec_and_test(&stack->count))
+		depot_free_stack(stack);
+}
+EXPORT_SYMBOL_GPL(stack_depot_put);
+
+void stack_depot_print(depot_stack_handle_t stack)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(stack, &entries);
+	if (nr_entries > 0)
+		stack_trace_print(entries, nr_entries, 0);
+}
+EXPORT_SYMBOL_GPL(stack_depot_print);
+
+int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
+		       int spaces)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(handle, &entries);
+	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
+						spaces) : 0;
+}
+EXPORT_SYMBOL_GPL(stack_depot_snprint);
+
+depot_stack_handle_t __must_check stack_depot_set_extra_bits(
+			depot_stack_handle_t handle, unsigned int extra_bits)
+{
+	union handle_parts parts = { .handle = handle };
+
+	/* Don't set extra bits on empty handles. */
+	if (!handle)
+		return 0;
+
+	parts.extra = extra_bits;
+	return parts.handle;
+}
+EXPORT_SYMBOL(stack_depot_set_extra_bits);
+
+unsigned int stack_depot_get_extra_bits(depot_stack_handle_t handle)
+{
+	union handle_parts parts = { .handle = handle };
+
+	return parts.extra;
+}
+EXPORT_SYMBOL(stack_depot_get_extra_bits);
+
+static int stats_show(struct seq_file *seq, void *v)
+{
+	/*
+	 * data race ok: These are just statistics counters, and approximate
+	 * statistics are ok for debugging.
+	 */
+	seq_printf(seq, "pools: %d\n", data_race(pools_num));
+	for (int i = 0; i < DEPOT_COUNTER_COUNT; i++)
+		seq_printf(seq, "%s: %ld\n", counter_names[i], data_race(counters[i]));
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(stats);
+
+static int depot_debugfs_init(void)
+{
+	struct dentry *dir;
+
+	if (stack_depot_disabled)
+		return 0;
+
+	dir = debugfs_create_dir("stackdepot", NULL);
+	debugfs_create_file("stats", 0444, dir, NULL, &stats_fops);
+	return 0;
+}
+late_initcall(depot_debugfs_init);