From 2b58c749b8c5244e259a0230bc57b10b010dc545 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Wed, 1 Jul 2026 15:58:10 -0400 Subject: [PATCH] sched/isolation: Defer freeing of cpumask memblock memory to initcall When testing a linux-next kernel with commit 59bd1d914bb5 ("memblock: warn when freeing reserved memory before memory map is initialized"), the following warning was hit when there was a "nohz_full" kernel boot parameter. Cannot free reserved memory because of deferred initialization of the memory map WARNING: mm/memblock.c:904 at __free_reserved_area+0xde/0xf0, CPU#0: swapper/0/0 : Call Trace: memblock_phys_free+0xcb/0x100 housekeeping_init+0x14c/0x170 start_kernel+0x207/0x450 x86_64_start_reservations+0x24/0x30 x86_64_start_kernel+0xda/0xe0 common_startup_64+0x13e/0x141 IOW, we shouldn't free memblock allocated memory so early in the boot process when memory map isn't fully initialized in deferred_init_memmap(). Fix it by saving the housekeeping cpumask memblock memory to be freed into a llist free list in housekeeping_init() and add a new housekeeping_late_init() helper to defer the actual freeing of memblock memory to when initcall's are being processed. The cpumask memblock memory is treated as a llist_node with the size of a "long" type which is also smallest cpumask size that can be allocated. The non-atomic version of the llist APIs are used as there is no contention. This commit depends on the presence of commit 7c2eee9c1367 ("memblock: don't touch memblock arrays when memblock_free() is called late") to prevent a KASAN UAF bug report [1]. [1] https://lore.kernel.org/lkml/20260505051821.1107133-1-longman@redhat.com/ Fixes: 27c3a5967f05 ("sched/isolation: Convert housekeeping cpumasks to rcu pointers") Signed-off-by: Waiman Long Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Frederic Weisbecker Reviewed-by: Phil Auld Link: https://patch.msgid.link/20260701195810.477326-1-longman@redhat.com --- kernel/sched/isolation.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index ef152d401fe2..156025ef81b7 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -8,6 +8,7 @@ * */ #include +#include #include #include "sched.h" @@ -27,6 +28,7 @@ struct housekeeping { }; static struct housekeeping housekeeping; +static __initdata LLIST_HEAD(memblock_freelist); bool housekeeping_enabled(enum hk_type type) { @@ -189,10 +191,22 @@ void __init housekeeping_init(void) WARN_ON_ONCE(cpumask_empty(omask)); cpumask_copy(nmask, omask); RCU_INIT_POINTER(housekeeping.cpumasks[type], nmask); - memblock_free(omask, cpumask_size()); + __llist_add((struct llist_node *)omask, &memblock_freelist); } } +static int __init housekeeping_late_init(void) +{ + struct llist_node *llnode, *pos, *t; + + /* Free allocated memblock memory, if any */ + llnode = __llist_del_all(&memblock_freelist); + llist_for_each_safe(pos, t, llnode) + memblock_free(pos, cpumask_size()); + return 0; +} +pure_initcall(housekeeping_late_init); + static void __init housekeeping_setup_type(enum hk_type type, cpumask_var_t housekeeping_staging) {