From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 13 Dec 2017 09:21:19 +0000 Subject: [PATCH] arm64: mm: Fix false positives in set_pte_at access/dirty race detection In-Reply-To: <8761ce54-ad67-1113-44e1-0d1606d12dbf@huawei.com> References: <1513079030-8557-1-git-send-email-will.deacon@arm.com> <8761ce54-ad67-1113-44e1-0d1606d12dbf@huawei.com> Message-ID: <20171213092119.GB27222@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Yisheng, On Wed, Dec 13, 2017 at 09:01:23AM +0800, Yisheng Xie wrote: > On 2017/12/12 19:43, Will Deacon wrote: > > Jiankang reports that our race detection in set_pte_at is firing when > > copying the page tables in dup_mmap as a result of a fork(). In this > > situation, the page table isn't actually live and so there is no way > > that we can race with a concurrent update from the hardware page table > > walker. > > > > This patch reworks the race detection so that we require either the > > mm to match the current active_mm (i.e. currently installed in our TTBR0) > > or the mm_users count to be greater than 1, implying that the page table > > could be live in another CPU. The mm_users check might still be racy, > > but we'll avoid false positives and it's not realistic to validate that > > all the necessary locks are held as part of this assertion. > > > > Cc: Yisheng Xie > > Reported-by: Jiankang Chen > > Tested-by: Jiankang Chen > > Signed-off-by: Will Deacon > > --- > > arch/arm64/include/asm/pgtable.h | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > index 3ff03a755c32..bdcc7f1c9d06 100644 > > --- a/arch/arm64/include/asm/pgtable.h > > +++ b/arch/arm64/include/asm/pgtable.h > > @@ -42,6 +42,8 @@ > > #include > > #include > > #include > > +#include > > +#include > > > > Do you have compiled kernel after apply this patch? In our environment, it will > fail to compile kernel if include file here(I will attach some log later). > Instead, we move these included file after mmdebug.h, and I do not know whether > this is just my compiler's problem: It compiles fine for me. Are you seeing a problem building this on top of mainline? If so, what is your .config? > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -42,6 +42,8 @@ > #include > #include > #include > +#include > +#include > > Sorry for not having told you this information. > > Thanks > Yisheng Xie > > compiler err log: ========== > [...] > include/linux/mm_types_task.h:60: Error: unknown mnemonic `struct' -- `struct page_frag{' > include/asm-generic/preempt.h:9: Error: unknown mnemonic `static' -- `static inline int preempt_count(void)' > include/linux/mm_types_task.h:61: Error: unknown mnemonic `struct' -- `struct page*page' > include/asm-generic/preempt.h:10: Error: junk at end of line, first unrecognized character is `{' > include/linux/mm_types_task.h:63: Error: unknown mnemonic `__u32' -- `__u32 offset' > include/asm-generic/preempt.h:11: Error: unknown mnemonic `return' -- `return READ_ONCE(((struct thread_info*)current)->preempt_count)' > include/linux/mm_types_task.h:64: Error: unknown mnemonic `__u32' -- `__u32 size' > [...] This looks like the includes are being pulled into an assembly file, but this part is guarded by #ifndef __ASSEMBLY__ so I can't see how that could happen. Will