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

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.