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Message-Id: <20220613131046.3009889-1-xianting.tian@linux.alibaba.com>
Date: Mon, 13 Jun 2022 21:10:46 +0800
From: Xianting Tian <xianting.tian@...ux.alibaba.com>
To: akpm@...ux-foundation.org, vbabka@...e.cz, ziy@...dia.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
stable@...r.kernel.org, huanyi.xj@...baba-inc.com,
guoren@...nel.org, zjb194813@...baba-inc.com,
tianhu.hh@...baba-inc.com,
Xianting Tian <xianting.tian@...ux.alibaba.com>
Subject: [RESEND PATCH] mm: page_alloc: validate buddy before check the migratetype
Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.")
added buddy check code. But unfortunately, this fix isn't backported to
linux-5.17.y and the former stable branches. The reason is it added wrong
fixes message:
Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable
pageblocks with others")
Actually, this issue is involved by commit:
commit d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
For RISC-V arch, the first 2M is reserved for sbi, so the start PFN is 512,
but it got buddy PFN 0 for PFN 0x2000:
0 = 0x2000 ^ (1 << 12)
With the illegal buddy PFN 0, it got an illegal buddy page, which caused
crash in __get_pfnblock_flags_mask().
With the patch, it can avoid the calling of get_pageblock_migratetype() if
it isn't buddy page.
Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
Cc: stable@...r.kernel.org
Reported-by: zjb194813@...baba-inc.com
Reported-by: tianhu.hh@...baba-inc.com
Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
---
mm/page_alloc.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b1caa1c6c887..5b423caa68fd 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1129,6 +1129,9 @@ static inline void __free_one_page(struct page *page,
buddy_pfn = __find_buddy_pfn(pfn, order);
buddy = page + (buddy_pfn - pfn);
+
+ if (!page_is_buddy(page, buddy, order))
+ goto done_merging;
buddy_mt = get_pageblock_migratetype(buddy);
if (migratetype != buddy_mt
--
2.17.1
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