[PATCH] stackdepot: Make max number of pools build-time configurable

[Matt Fleming <matt@readmodwrite.com>]

From: Matt Fleming <mfleming@cloudflare.com>

We're hitting the WARN in depot_init_pool() about reaching the stack
depot limit. My assumption is because we have long stacks that don't
dedup very well.

Introduce a new config to allow users to set the number of maximum stack
depot pools at build time. Also, turn the silent capping into a
build-time assert to provide more obvious feedback when users set this
value too high.

Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 lib/Kconfig      | 6 ++++++
 lib/stackdepot.c | 9 ++++-----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/Kconfig b/lib/Kconfig
index b38849af6f13..2c5af89daff9 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -720,6 +720,12 @@ config STACKDEPOT_MAX_FRAMES
 	default 64
 	depends on STACKDEPOT
 
+config STACKDEPOT_MAX_POOLS
+	int "Maximum number of stack depot pools to store stack traces"
+	range 1024 131071
+	default 8192
+	depends on STACKDEPOT
+
 config REF_TRACKER
 	bool
 	depends on STACKTRACE_SUPPORT
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 245d5b416699..1c24230b4a37 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -36,11 +36,7 @@
 #include <linux/memblock.h>
 #include <linux/kasan-enabled.h>
 
-#define DEPOT_POOLS_CAP 8192
-/* The pool_index is offset by 1 so the first record does not have a 0 handle. */
-#define DEPOT_MAX_POOLS \
-	(((1LL << (DEPOT_POOL_INDEX_BITS)) - 1 < DEPOT_POOLS_CAP) ? \
-	 (1LL << (DEPOT_POOL_INDEX_BITS)) - 1 : DEPOT_POOLS_CAP)
+#define DEPOT_MAX_POOLS CONFIG_STACKDEPOT_MAX_POOLS
 
 static bool stack_depot_disabled;
 static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
@@ -245,6 +241,9 @@ static bool depot_init_pool(void **prealloc)
 {
 	lockdep_assert_held(&pool_lock);
 
+	/* The pool_index is offset by 1 so the first record does not have a 0 handle. */
+	BUILD_BUG_ON((1LL << (DEPOT_POOL_INDEX_BITS)) - 1 < DEPOT_MAX_POOLS);
+
 	if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {
 		/* Bail out if we reached the pool limit. */
 		WARN_ON_ONCE(pools_num > DEPOT_MAX_POOLS); /* should never happen */
-- 
2.34.1