linux-kernel - RE: [PATCH 3/4] sparc: convert mdesc_handle.refcnt from atomic_t to refcount

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Message-ID: <2236FBA76BA1254E88B949DDB74E612B41C87070@IRSMSX102.ger.corp.intel.com>
Date:   Mon, 3 Apr 2017 16:06:44 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     David Miller <davem@...emloft.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "ishkamiel@...il.com" <ishkamiel@...il.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "dwindsor@...il.com" <dwindsor@...il.com>
Subject: RE: [PATCH 3/4] sparc: convert mdesc_handle.refcnt from atomic_t to
 refcount_t

> From: "Reshetova, Elena" <elena.reshetova@...el.com>
> Date: Mon, 3 Apr 2017 07:28:01 +0000
> 
> >
> >> From: Elena Reshetova <elena.reshetova@...el.com>
> >> Date: Mon, 20 Feb 2017 13:06:20 +0200
> >>
> >> > refcount_t type and corresponding API should be
> >> > used instead of atomic_t when the variable is used as
> >> > a reference counter. This allows to avoid accidental
> >> > refcounter overflows that might lead to use-after-free
> >> > situations.
> >> >
> >> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> >> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> >> > Signed-off-by: Kees Cook <keescook@...omium.org>
> >> > Signed-off-by: David Windsor <dwindsor@...il.com>
> >>
> >> Acked-by: David S. Miller <davem@...emloft.net>
> >
> > Hi David,
> >
> > Would you be able to propagate this patch further or should I send
> > it (with your acked-by) once more to specific list/maintainer for
> > the inclusion?
> 
> I'm generally not happy with the refcount_t and the added overhead it
> has compared to the existing atomic_t operations.
> 
> I know it is going to make a difference for networking.
> 
> I understand that this sparc case is a slow path, but I know that if
> we just apply all of these refcount_t conversions, there will be no
> work done to address the performance issues.

I think we will have to address the performance problems in places where we can see it matters. 
The problem is that so far noone told us how to measure in any reasonable way the overhead neither in networking, not in mm changes. 
If this change is a slow path, why would it matter for *this particular patch*?

Best Regards,
Elena.
 
> So I'm reluctant to ACK in any way these refcount_t conversions,
> sorry.