linux-kernel - Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache

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Message-ID: <20160825093054.GB20748@e104818-lin.cambridge.arm.com>
Date:   Thu, 25 Aug 2016 10:30:54 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Steve Capper <Steve.Capper@....com>,
        David Woods <dwoods@...hip.com>,
        Tianhong Ding <dingtianhong@...wei.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Xinwei Hu <huxinwei@...wei.com>, Zefan Li <lizefan@...wei.com>,
        "fangwei (I)" <fangwei1@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        wangxuefeng 00195527 <wxf.wang@...ilicon.com>
Subject: Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is
 dirty when munmap

On Thu, Aug 25, 2016 at 09:42:26AM +0800, Leizhen (ThunderTown) wrote:
> On 2016/8/24 18:30, Catalin Marinas wrote:
> >>>>>>>>>> On 2016/7/8 21:54, Catalin Marinas wrote:
> >>>>>>>>>>> ------------8<----------------
> >>>>>>>>>>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> >>>>>>>>>>> index dbd12ea8ce68..c753fa804165 100644
> >>>>>>>>>>> --- a/arch/arm64/mm/flush.c
> >>>>>>>>>>> +++ b/arch/arm64/mm/flush.c
> >>>>>>>>>>> @@ -75,7 +75,8 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr)
> >>>>>>>>>>>  	if (!page_mapping(page))
> >>>>>>>>>>>  		return;
> >>>>>>>>>>>  
> >>>>>>>>>>> -	if (!test_and_set_bit(PG_dcache_clean, &page->flags))
> >>>>>>>>>>> +	if (!test_and_set_bit(PG_dcache_clean, &page->flags) ||
> >>>>>>>>>>> +	    PageDirty(page))
> >>>>>>>>>>>  		sync_icache_aliases(page_address(page),
> >>>>>>>>>>>  				    PAGE_SIZE << compound_order(page));
> >>>>>>>>>>>  	else if (icache_is_aivivt())
> >>>>>>>>>>> ----------------8<---------------------
[...]
> > While we indeed see failures on multiple filesystem types, I wonder
> > whether this test case is actually expected to work. If I modify the
> > test to pass O_TRUNC to open(), I can no longer see failures. So any
> > standard tool that copies/creates executable files (gcc, dpkg, cp, rsync
> > etc.) wouldn't encounter such issues since they truncate the original
> > file and old page cache pages would be removed.
> > 
> > Do you have a real use-case where a task mmap's an executable file,
> > modifies it in place and expects another task to see the new
> > instructions without user-space cache maintenance?
> 
> No, it's just a test case created by testers.

In this case I propose we ignore this patch and you adjust the test to
use O_TRUNC, at least until we find a real scenario where this would
matter.

-- 
Catalin