From 8f56ea8e0706d92774603260779c7032f03ef3ac Mon Sep 17 00:00:00 2001 From: Caleb Kan Date: Thu, 22 Oct 2026 09:33:30 +0100 Subject: [PATCH] stackdepot: stop preallocating after the final pool depot_init_pool() decides whether another pool is needed before it increments pools_num. When it registers the last allowed pool, pools_num is still one below stack_max_pools, so the existing comparison clears new_pool. With new_pool cleared, stack_depot_save_flags() can allocate another order-2 pool after a lookup miss. depot_keep_new_pool() retains its pointer in the global new_pool, so the allocation is not lost. However, pools_num has already reached stack_max_pools, and depot_init_pool() rejects every attempt to register the pool. It remains allocated and unusable until reboot. The non-NULL pointer prevents later saves from allocating more spare pools. Account for the pool being registered in the limit check so registering the final pool installs STACK_DEPOT_POISON and prevents the extra allocation. Link: https://lore.kernel.org/20261022083330.3159793-1-matt@readmodwrite.com Fixes: 31639fd6cebd ("stackdepot: use variable size records for non-evictable entries") Signed-off-by: Caleb Kan Signed-off-by: Matt Fleming Signed-off-by: Andrew Morton Reviewed-by: Marco Elver Cc: Andrey Konovalov Cc: Mikhail Gavrilov Cc: Caleb Kan Cc: Alexander Potapenko Cc: Dmitry Vyukov Cc: Vlastimil Babka Cc: --- lib/stackdepot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/lib/stackdepot.c b/lib/stackdepot.c index dd2717ff94bf..90c52f2e0d3f 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -323,7 +323,7 @@ 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 < stack_max_pools) + if (pools_num + 1 < stack_max_pools) WRITE_ONCE(new_pool, NULL); else WRITE_ONCE(new_pool, STACK_DEPOT_POISON);