Hi, under some rare occasion I run into the following crash: [ 41.417606] pstate: 80400005 (Nzcv daif +PAN -UAO) [ 41.422406] pc : set_pfnblock_flags_mask+0x50/0x94 [ 41.427193] lr : compaction_alloc+0x220/0x804 [ 41.431544] sp : ffffffc01104bb10 [ 41.434852] x29: ffffffc01104bb10 x28: ffffffc010e5b500 [ 41.440165] x27: 0000000000098000 x26: ffffffc010e5b500 [ 41.445477] x25: 0000000000000066 x24: 0000000000090800 [ 41.450789] x23: 0000000000000200 x22: 0000000000084000 [ 41.456093] x21: ffffffc010e82000 x20: ffffffc010b88000 [ 41.461396] x19: ffffffc01104bd70 x18: 0000000000000000 [ 41.466700] x17: f1f24e35df34dda4 x16: 6b3f63a0e1157268 [ 41.472004] x15: 4b3990ec2568ada0 x14: 757ebc126939cb5f [ 41.477308] x13: 9df9488aba179ccb x12: 0000000000000000 [ 41.482612] x11: 0000000000000000 x10: ffffffc010c5fc30 [ 41.487916] x9 : ffffff801eea7c00 x8 : 000000001bf00000 [ 41.493219] x7 : 0000000000000000 x6 : 000000000000003f [ 41.498525] x5 : 0000000000000108 x4 : 1000000000000000 [ 41.503835] x3 : 0000000000000021 x2 : 000000000000003c [ 41.509139] x1 : 0000000000000001 x0 : 0000000000000003 [ 41.514443] Call trace: [ 41.516887] set_pfnblock_flags_mask+0x50/0x94 [ 41.521330] migrate_pages+0x90/0x7f0 [ 41.524992] compact_zone+0x854/0x9f0 [ 41.528647] kcompactd_do_work+0x168/0x230 [ 41.532734] kcompactd+0x58/0x140 [ 41.536043] kthread+0x120/0x124 [ 41.539263] ret_from_fork+0x10/0x24 [ 41.542835] Code: d346fc43 4b0000c2 8b030ce5 9ac22084 (f86378e0) [ 41.548925] ---[ end trace 731400a587304db3 ]--- I've pin-pointed it down to pageblock_flags pointer being initialized to NULL under certain conditions. I don't know why this happens. Maybe it is some obscure race condition which only shows up on my system. Nonetheless, I've made a fix for this in the attached patch. It adds sanity checking and protects the system for crashing. I think it is better to be safe than sorry. -- Best Regards, Markus |
From 2ff8267436362532848b73b7beab7fd36015b0c5 Mon Sep 17 00:00:00 2001 From: Markus Gothe <markus.gothe@xxxxxxxxxx> Date: Thu, 2 May 2024 15:36:36 +0200 Subject: [PATCH] page_alloc.c: Sanity check for NULL pointers. get_pageblock_bitmap() might in very rare cicumstances return NULL which must be handled accordingly or otherwise we will end up with a kernel crash. --- mm/page_alloc.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 540af9a120e6..ab230e349862 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -486,6 +486,9 @@ static __always_inline unsigned long __get_pfnblock_flags_mask(struct page *page unsigned long word; bitmap = get_pageblock_bitmap(page, pfn); + if (unlikely(bitmap == NULL)) + return 0; + bitidx = pfn_to_bitidx(page, pfn); word_bitidx = bitidx / BITS_PER_LONG; bitidx &= (BITS_PER_LONG-1); @@ -528,6 +531,9 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); bitmap = get_pageblock_bitmap(page, pfn); + if (unlikely(bitmap == NULL)) + return; + bitidx = pfn_to_bitidx(page, pfn); word_bitidx = bitidx / BITS_PER_LONG; bitidx &= (BITS_PER_LONG-1); -- 2.43.2
