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From: Borislav Petkov <bp@alien8.de>
To: "Zheng, Lv" <lv.zheng@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>,
	Jiri Kosina <jkosina@suse.cz>, Borislav Petkov <bp@suse.de>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <lenb@kernel.org>, "Luck, Tony" <tony.luck@intel.com>,
	Tomasz Nowicki <tomasz.nowicki@linaro.org>,
	"Chen, Gong" <gong.chen@linux.intel.com>,
	Wolfram Sang <wsa@the-dreams.de>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 5/5] GHES: Make NMI handler have a single reader
Date: Mon, 27 Apr 2015 10:46:31 +0200	[thread overview]
Message-ID: <20150427084631.GA6774@pd.tnic> (raw)
In-Reply-To: <1AE640813FDE7649BE1B193DEA596E880270F2B2@SHSMSX101.ccr.corp.intel.com>

On Mon, Apr 27, 2015 at 03:16:00AM +0000, Zheng, Lv wrote:
> > @@ -840,7 +840,9 @@ static int ghes_notify_nmi(unsigned int cmd, struct pt_regs *regs)
> >  	struct ghes *ghes;
> >  	int sev, ret = NMI_DONE;
> > 
> > -	raw_spin_lock(&ghes_nmi_lock);
> > +	if (!atomic_add_unless(&ghes_in_nmi, 1, 1))
> > +		return ret;
> > +
> 
> Just a simple question.
> Why not just using cmpxchg here instead of atomic_add_unless so that no atomic_dec will be needed.

What do you think atomic_add_unless ends up doing:

#APP
# 177 "./arch/x86/include/asm/atomic.h" 1
	.pushsection .smp_locks,"a"
.balign 4
.long 671f - .
.popsection
671:
	lock; cmpxchgl %edx,ghes_in_nmi(%rip)	# D.37056, MEM[(volatile u32 *)&ghes_in_nmi]
# 0 "" 2
#NO_APP

And you need to atomic_dec() so that another reader can enter, i.e. how
the exclusion primitive works.

Or did you have something else in mind?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--

  reply	other threads:[~2015-04-27  8:46 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-27  9:22 [RFC PATCH 0/5] GHES NMI handler cleanup Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 1/5] GHES: Carve out error queueing in a separate function Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 2/5] GHES: Carve out the panic functionality Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 3/5] GHES: Panic right after detection Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 4/5] GHES: Elliminate double-loop in the NMI handler Borislav Petkov
2015-03-27  9:22 ` [RFC PATCH 5/5] GHES: Make NMI handler have a single reader Borislav Petkov
2015-04-01  7:45   ` Jiri Kosina
2015-04-01 13:49     ` Borislav Petkov
2015-04-23  8:39       ` Jiri Kosina
2015-04-23  8:59         ` Borislav Petkov
2015-04-23 18:00           ` Luck, Tony
2015-04-27 20:23             ` Borislav Petkov
2015-04-28 14:30     ` Don Zickus
2015-04-28 14:42       ` Don Zickus
2015-04-28 14:55       ` Borislav Petkov
2015-04-28 15:35         ` Don Zickus
2015-04-28 16:22           ` Borislav Petkov
2015-04-28 18:44             ` Don Zickus
2015-05-04 15:40               ` Borislav Petkov
2015-04-27  3:16   ` Zheng, Lv
2015-04-27  8:46     ` Borislav Petkov [this message]
2015-04-28  0:44       ` Zheng, Lv
2015-04-28  2:24       ` Zheng, Lv
2015-04-28  7:38         ` Borislav Petkov
2015-04-28 13:38   ` Zheng, Lv
2015-04-28 13:59     ` Borislav Petkov
2015-04-29  0:24       ` Zheng, Lv
2015-04-29  0:49       ` Zheng, Lv
2015-04-29  8:13         ` Borislav Petkov
2015-04-30  8:05           ` Zheng, Lv
2015-04-30  8:48             ` Borislav Petkov
2015-05-02  0:34               ` Zheng, Lv

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