lib/stackdepot: allow users to evict stack traces

Add stack_depot_put, a function that decrements the reference counter on a
stack record and removes it from the stack depot once the counter reaches
0.

Internally, when removing a stack record, the function unlinks it from the
hash table bucket and returns to the freelist.

With this change, the users of stack depot can call stack_depot_put when
keeping a stack trace in the stack depot is not needed anymore.  This
allows avoiding polluting the stack depot with irrelevant stack traces and
thus have more space to store the relevant ones before the stack depot
reaches its capacity.

Link: https://lkml.kernel.org/r/1d1ad5692ee43d4fc2b3fd9d221331d30b36123f.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 36 insertions, 1 deletions

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 911dee11bf39..c1b31160f4b4 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -394,7 +394,7 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
 	size_t offset = parts.offset << DEPOT_STACK_ALIGN;
 	struct stack_record *stack;
 
-	lockdep_assert_held_read(&pool_rwlock);
+	lockdep_assert_held(&pool_rwlock);
 
 	if (parts.pool_index > pools_num) {
 		WARN(1, "pool index %d out of bounds (%d) for stack id %08x\n",
@@ -410,6 +410,14 @@ static struct stack_record *depot_fetch_stack(depot_stack_handle_t handle)
 	return stack;
 }
 
+/* Links stack into the freelist. */
+static void depot_free_stack(struct stack_record *stack)
+{
+	lockdep_assert_held_write(&pool_rwlock);
+
+	list_add(&stack->list, &free_stacks);
+}
+
 /* Calculates the hash for a stack. */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 {
@@ -592,6 +600,33 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 }
 EXPORT_SYMBOL_GPL(stack_depot_fetch);
 
+void stack_depot_put(depot_stack_handle_t handle)
+{
+	struct stack_record *stack;
+	unsigned long flags;
+
+	if (!handle || stack_depot_disabled)
+		return;
+
+	write_lock_irqsave(&pool_rwlock, flags);
+
+	stack = depot_fetch_stack(handle);
+	if (WARN_ON(!stack))
+		goto out;
+
+	if (refcount_dec_and_test(&stack->count)) {
+		/* Unlink stack from the hash table. */
+		list_del(&stack->list);
+
+		/* Free stack. */
+		depot_free_stack(stack);
+	}
+
+out:
+	write_unlock_irqrestore(&pool_rwlock, flags);
+}
+EXPORT_SYMBOL_GPL(stack_depot_put);
+
 void stack_depot_print(depot_stack_handle_t stack)
 {
 	unsigned long *entries;