Subject: Re: linux-next: boot failure after merge of the memblock tree

From: Mike Rapoport <[email-masked]>
Date: Fri, 25 Oct 2024 09:53:14 +0300

Hi Stephen,

On Tue, Oct 22, 2024 at 05:39:21PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> After merging the memblock tree, today's linux-next build
> (powerpc_pseries_le_defconfig) failed my qemu boot test like this:
> 
> mem auto-init: stack:all(zero), heap alloc:off, heap free:off
> BUG: Unable to handle kernel data access on read at 0x00001878
> Faulting instruction address: 0xc0000000004f00e4
> Oops: Kernel access of bad area, sig: 7 [#1]
> LE PAGE_SIZE=4K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
> Modules linked in:
> CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.12.0-rc4-06078-g367eaba2691a #1
> Hardware name: IBM pSeries (emulated by qemu) POWER10 (architected) 0x801200 0xf000006 of:SLOF,HEAD pSeries
> NIP:  c0000000004f00e4 LR: c000000000489df8 CTR: 0000000000000000
> REGS: c0000000028cfae0 TRAP: 0300   Not tainted  (6.12.0-rc4-06078-g367eaba2691a)
> MSR:  8000000002001033 <SF,VEC,ME,IR,DR,RI,LE>  CR: 84000240  XER: 00000000
> CFAR: c0000000004f2c48 DAR: 0000000000001878 DSISR: 00080000 IRQMASK: 3 
> GPR00: c00000000204994c c0000000028cfd80 c0000000016a4300 c00c000000040000 
> GPR04: 0000000000000001 0000000000001000 0000000000000007 c000000002a11178 
> GPR08: 0000000000000000 0000000000001800 c00000007fffe720 0000000000002001 
> GPR12: 0000000000000000 c000000002a6a000 0000000000000000 00000000018855c0 
> GPR16: c000000002940270 c00c000000000000 0000000000040000 0000000000000000 
> GPR20: 0000000000000000 ffffffffffffffff 0000000000000001 ffffffffffffffff 
> GPR24: 00c0000000000000 0000000000000000 0000000000000000 0000000008000000 
> GPR28: 0000000000000000 0000000000002a6b 0000000000000000 0000000000001000 
> NIP [c0000000004f00e4] set_pfnblock_flags_mask+0x74/0x140
> LR [c000000000489df8] reserve_bootmem_region+0x2a8/0x2c0
> Call Trace:
> c0000000028cfd80] [c0000000028cfdd0] 0xc0000000028cfdd0 (unreliable)
> c0000000028cfe20] [c00000000204994c] memblock_free_all+0x144/0x2d0
> c0000000028cfea0] [c000000002016354] mem_init+0x5c/0x70
> c0000000028cfec0] [c00000000204547c] mm_core_init+0x158/0x1dc
> c0000000028cff30] [c000000002004350] start_kernel+0x608/0x944
> c0000000028cffe0] [c00000000000e99c] start_here_common+0x1c/0x20
> Code: 4182000c 79082d28 7d4a4214 e9230000 3d020137 38e8ce78 79284620 792957a0 79081f24 79295d24 7d07402a 7d284a14 <e9090078> 7c254040 41800094 e9290088 
> ---[ end trace 0000000000000000 ]---
> 
> Kernel panic - not syncing: Attempted to kill the idle task!
> 
> Caused by commit
> 
>   ad48825232a9 ("memblock: uniformly initialize all reserved pages to MIGRATE_MOVABLE")
> 
> I bisected the failure to this commit and have reverted it for today.

Apparently set_pfnblock_flags_mask() is unhappy when called for
uninitialized struct page. With the patch below

qemu-system-ppc64el -M pseries -cpu power10 -smp 16 -m 32G -vga none -nographic -kernel $KERNEL

boots up to mounting root filesystem.
 
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 49dbd30e71ad..2395970314e7 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -723,10 +723,10 @@ static void __meminit init_reserved_page(unsigned long pfn, int nid)
 			break;
 	}
 
+	__init_single_page(pfn_to_page(pfn), pfn, zid, nid);
+
 	if (pageblock_aligned(pfn))
 		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_MOVABLE);
-
-	__init_single_page(pfn_to_page(pfn), pfn, zid, nid);
 }
 #else
 static inline void pgdat_set_deferred_range(pg_data_t *pgdat) {}

> -- 
> Cheers,
> Stephen Rothwell

-- 
Sincerely yours,
Mike.