在 2022/6/14 上午12:08, Guo Ren 写道:
On Mon, Jun 13, 2022 at 9:11 PM Xianting Tian xianting.tian@linux.alibaba.com wrote:
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)
How did we get 0? （Try it in gdb) (gdb) p /x (0x2000 ^ (1<<12)) $3 = 0x3000
I think it got buddy PFN 0 for PFN 0x1000, right? (gdb) p /x (0x1000 ^ (1<<12)) $4 = 0x0
Sorry, it is a typo, the order is 0xd = 13, not 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@vger.kernel.org Reported-by: zjb194813@alibaba-inc.com Reported-by: tianhu.hh@alibaba-inc.com Signed-off-by: Xianting Tian xianting.tian@linux.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))Right, we need to check the buddy_pfn valid, because some SoCs would start dram address with an offset that has an order smaller than MAX_ORDER.
goto done_merging; buddy_mt = get_pageblock_migratetype(buddy); if (migratetype != buddy_mt-- 2.17.1
Fixup the comment and
Reviewed-by: Guo Ren guoren@kernel.org