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stackdepot: make max number of pools boot-time configurable

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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: Matt Fleming <mfleming@cloudflare.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Marco 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matt Fleming 2025-07-18 16:39:28 +01:00 • committed by Andrew Morton
parent 6c6d8f8ba7
commit ed4f142f72
2 changed files with 63 additions and 9 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View file

@ -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.

67
lib/stackdepot.c
View file

@ -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);