Commit ed4f142f authored by Matt Fleming's avatar Matt Fleming Committed by Andrew Morton
Browse files

stackdepot: make max number of pools boot-time configurable 

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

Introduce a new start-up parameter to allow users to set the number of
maximum stack depot pools.

Link: https://lkml.kernel.org/r/20250718153928.94229-1-matt@readmodwrite.com


Signed-off-by: default avatarMatt Fleming <mfleming@cloudflare.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarMarco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6c6d8f8b

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -7029,6 +7029,11 @@ 
			consumed by the stack hash table. By default this is set

			to false.



	stack_depot_max_pools= [KNL,EARLY]

			Specify the maximum number of pools to use for storing

			stack traces. Pools are allocated on-demand up to this

			limit. Default value is 8191 pools.



	stacktrace	[FTRACE]

			Enabled the stack tracer on boot up.

lib/stackdepot.c

+58 −9
Original line number Diff line number Diff line
@@ -36,11 +36,11 @@ 
#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)

/*

 * 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);
@@ -62,7 +62,7 @@ static unsigned int stack_bucket_number_order; 
static unsigned int stack_hash_mask;



/* Array of memory regions that store stack records. */

static void *stack_pools[DEPOT_MAX_POOLS];

static void **stack_pools;

/* Newly allocated pool that is not yet added to stack_pools. */

static void *new_pool;

/* Number of pools in stack_pools. */
@@ -101,6 +101,34 @@ static int __init disable_stack_depot(char *str) 
}

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. */
@@ -182,6 +210,17 @@ int __init stack_depot_early_init(void) 
	}

	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;

}
@@ -231,6 +270,16 @@ int stack_depot_init(void) 
	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);
@@ -245,9 +294,9 @@ static bool depot_init_pool(void **prealloc) 
{

	lockdep_assert_held(&pool_lock);



	if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {

	if (unlikely(pools_num >= stack_max_pools)) {

		/* Bail out if we reached the pool limit. */

		WARN_ON_ONCE(pools_num > DEPOT_MAX_POOLS); /* should never happen */

		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;
@@ -273,7 +322,7 @@ static bool depot_init_pool(void **prealloc) 
	 * NULL; do not reset to NULL if we have reached the maximum number of

	 * pools.

	 */

	if (pools_num < DEPOT_MAX_POOLS)

	if (pools_num < stack_max_pools)

		WRITE_ONCE(new_pool, NULL);

	else

		WRITE_ONCE(new_pool, STACK_DEPOT_POISON);