Re: Warning from free_reserved_area() in next-20260325+

Mike Rapoport
2026-03-27T17:12:31Z

Hi Bert,

On Fri, Mar 27, 2026 at 03:01:08PM +0100, Bert Karwatzki wrote:
> Starting with linux next-20260325 I see the following warning early in the
> boot process of a machine running debian stable (trixie) (except for the kernel):

Thanks for the report!

> [ 0.027118] [ T0] ------------[ cut here ]------------
> [ 0.027118] [ T0] Cannot free reserved memory because of deferred initialization of the memory map
> [ 0.027119] [ T0] WARNING: mm/memblock.c:904 at __free_reserved_area+0xa9/0xc0, CPU#0: swapper/0/0
> [ 0.027122] [ T0] Modules linked in:
> [ 0.027123] [ T0] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.0.0-rc5-next-20260326-master #385 PREEMPT_RT
> [ 0.027125] [ T0] Hardware name: ASUS System Product Name/ROG STRIX B850-F GAMING WIFI, BIOS 1627 02/05/2026
> [ 0.027125] [ T0] RIP: 0010:__free_reserved_area+0xa9/0xc0
> [ 0.027126] [ T0] Code: 48 89 df 48 89 ee e8 06 fe ff ff 48 89 c3 48 39 e8 72 a0 5b 4c 89 e8 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 8d 3d 97 c2 c6 00 <67> 48 0f b9 3a 45 31 ed eb df 66 66 2e 0f 1f 84 00 00 00 00 00 66
> [ 0.027127] [ T0] RSP: 0000:ffffffff9b203e98 EFLAGS: 00010202
> [ 0.027128] [ T0] RAX: 0000000e91c00001 RBX: ffffffff9b100c0f RCX: 0000000080000001
> [ 0.027128] [ T0] RDX: 00000000000000cc RSI: 0000000e2d42d000 RDI: ffffffff9b32ef60
> [ 0.027128] [ T0] RBP: ffff9eeafdd6fbc0 R08: 0000000000000000 R09: 0000000000000001
> [ 0.027129] [ T0] R10: 0000000000001000 R11: 8000000000000163 R12: 000000000000006f
> [ 0.027129] [ T0] R13: 0000000000000000 R14: 0000000000000045 R15: 000000005c8a1000
> [ 0.027129] [ T0] FS: 0000000000000000(0000) GS:ffff9eeb21c05000(0000) knlGS:0000000000000000
> [ 0.027130] [ T0] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 0.027130] [ T0] CR2: ffff9ee8ad801000 CR3: 0000000e2ce1e000 CR4: 0000000000f50ef0
> [ 0.027131] [ T0] PKRU: 55555554
> [ 0.027131] [ T0] Call Trace:
> [ 0.027132] [ T0] <TASK>
> [ 0.027132] [ T0] free_reserved_area+0x89/0xd0
> [ 0.027133] [ T0] alternative_instructions+0xee/0x110
> [ 0.027136] [ T0] arch_cpu_finalize_init+0x10f/0x160
> [ 0.027138] [ T0] start_kernel+0x686/0x710
> [ 0.027140] [ T0] x86_64_start_reservations+0x24/0x30
> [ 0.027141] [ T0] x86_64_start_kernel+0xd4/0xe0
> [ 0.027142] [ T0] common_startup_64+0x13e/0x141
> [ 0.027143] [ T0] </TASK>
> [ 0.027144] [ T0] ---[ end trace 0000000000000000 ]---

Does this patch fix it for you?

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index e87da25d1236..62936a3bde19 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -2448,19 +2448,31 @@ void __init alternative_instructions(void)
__smp_locks, __smp_locks_end,
_text, _etext);
}
+#endif

+ restart_nmi();
+ alternatives_patched = 1;
+
+ alt_reloc_selftest();
+}
+
+#ifdef CONFIG_SMP
+/*
+ * With CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled we can free_init_pages() only
+ * after the deferred initialization of the memory map is complete.
+ */
+static int __init free_smp_locks(void)
+{
if (!uniproc_patched || num_possible_cpus() == 1) {
free_init_pages("SMP alternatives",
(unsigned long)__smp_locks,
(unsigned long)__smp_locks_end);
}
-#endif

- restart_nmi();
- alternatives_patched = 1;
-
- alt_reloc_selftest();
+ return 0;
}
+arch_initcall(free_smp_locks);
+#endif

/**
* text_poke_early - Update instructions on a live kernel at boot time

> Bert Karwatzki

--
Sincerely yours,
Mike.