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From: Thomas Gleixner <tglx@linutronix.de>
To: Huacai Chen <chenhuacai@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>,
	Huacai Chen <chenhuacai@loongson.cn>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Darren Hart <dvhart@infradead.org>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	"open list:MIPS" <linux-mips@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Xuefeng Li <lixuefeng@loongson.cn>,
	Jiaxun Yang <jiaxun.yang@flygoat.com>,
	Hongchen Zhang <zhanghongchen@loongson.cn>
Subject: Re: [PATCH] futex: Fix fault_in_user_writeable()
Date: Tue, 17 Aug 2021 11:05:15 +0200	[thread overview]
Message-ID: <87y290o304.ffs@tglx> (raw)
In-Reply-To: <CAAhV-H6=MbBFwgxT75Bqr5SY0e5E6gtpCUCZhrVgFE_h1A0q2A@mail.gmail.com>

Huacai,

On Tue, Aug 17 2021 at 15:38, Huacai Chen wrote:
> On Tue, Aug 17, 2021 at 3:07 PM Thomas Gleixner <tglx@linutronix.de> wrote:
> On X86, it returns 0; on MIPS64 without patch, it hangs in kernel; on
> MIPS64 with this patch, it returns -1.

As expected.

> Then, I want to know, on "W implies R" archs (such as X86), should it
> return 0? Maybe return -1 is more reasonable? (because the VMA is
> marked as write-only). If this program should return -1, then I don't
> think this is a MIPS-specific problem.

No. mmap(.., PROT_WRITE...) is simply impossible on x86 and implies
PROT_READ as documented in mmap(2).

So why should this fail and only fail in the fault case, but succeed
when the PTE is already established?

Thanks,

        tglx

  reply	other threads:[~2021-08-17  9:05 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-16  6:54 [PATCH] futex: Fix fault_in_user_writeable() Huacai Chen
2021-08-16 18:27 ` Davidlohr Bueso
2021-08-16 19:03   ` Thomas Gleixner
2021-08-17  1:53     ` Huacai Chen
2021-08-17  7:07       ` Thomas Gleixner
2021-08-17  7:38         ` Huacai Chen
2021-08-17  9:05           ` Thomas Gleixner [this message]
2021-08-17  9:45             ` Peter Zijlstra
2021-08-17 12:27               ` Huacai Chen
2021-08-17  9:22       ` Peter Zijlstra

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