Messages in this thread | | | Subject | Re: [RESEND PATCH] mm: page_alloc: validate buddy before check the migratetype | From | Xianting Tian <> | Date | Tue, 14 Jun 2022 09:26:48 +0800 |
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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 > Sorry, the order is 0xd = 13, not 12, it is a typo. > I think it got buddy PFN 0 for PFN 0x1000, right? > (gdb) p /x (0x1000 ^ (1<<12)) > $4 = 0x0 > >> 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> >
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