From: Thomas Gleixner <tglx@linutronix.de>
To: Will Deacon <will.deacon@arm.com>
Cc: Jiri Slaby <jslaby@suse.cz>,
linux-kernel@vger.kernel.org, Richard Henderson <rth@twiddle.net>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Matt Turner <mattst88@gmail.com>,
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Catalin Marinas <catalin.marinas@arm.com>,
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Tony Luck <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
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Ralf Baechle <ralf@linux-mips.org>,
Jonas Bonn <jonas@southpole.se>,
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Stafford Horne <shorne@gmail.com>,
"James E.J. Bottomley" <jejb@parisc-linux.org>,
Helge Deller <deller@gmx.de>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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Subject: Re: [PATCH 1/1] futex: remove duplicated code
Date: Mon, 22 May 2017 23:11:33 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.20.1705222259580.2407@nanos> (raw)
In-Reply-To: <20170515131644.GA3605@arm.com>
On Mon, 15 May 2017, Will Deacon wrote:
> Hi Jiri,
>
> On Mon, May 15, 2017 at 03:07:42PM +0200, Jiri Slaby wrote:
> > There is code duplicated over all architecture's headers for
> > futex_atomic_op_inuser. Namely op decoding, access_ok check for uaddr,
> > and comparison of the result.
> >
> > Remove this duplication and leave up to the arches only the needed
> > assembly which is now in arch_futex_atomic_op_inuser.
> >
> > Note that s390 removed access_ok check in d12a29703 ("s390/uaccess:
> > remove pointless access_ok() checks") as access_ok there returns true.
> > We introduce it back to the helper for the sake of simplicity (it gets
> > optimized away anyway).
>
> Whilst I think this is a good idea, the code in question actually results
> in undefined behaviour per the C spec and is reported by UBSAN. See my
> patch fixing arm64 here (which I'd forgotten about):
>
> https://www.spinics.net/lists/linux-arch/msg38564.html
>
> But, as stated in the thread above, I think we should go a step further
> and remove FUTEX_OP_{OR,ANDN,XOR,OPARG_SHIFT} altogether. They don't
> appear to be used by userspace, and this whole thing is a total mess.
You wish. The constants are not used, but FUTEX_WAKE_OP _IS_ used by
glibc. They only have one argument it seems:
#define FUTEX_OP_CLEAR_WAKE_IF_GT_ONE ((4 << 24) | 1)
but I'm pretty sure that there is enough (probably horrible) code (think
java) out there using FUTEX_WAKE_OP for whatever (non)sensical reasons in
any available combination.
Thanks,
tglx
next prev parent reply other threads:[~2017-05-22 21:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-15 13:07 [PATCH 1/1] futex: remove duplicated code Jiri Slaby
2017-05-15 13:16 ` Will Deacon
2017-05-17 8:01 ` Jiri Slaby
2017-05-18 17:30 ` Will Deacon
2017-05-22 21:11 ` Thomas Gleixner [this message]
2017-05-25 14:28 ` Will Deacon
2017-05-26 6:54 ` Thomas Gleixner
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