From: konrad.wilk@oracle•com (Konrad Rzeszutek Wilk)
To: linux-arm-kernel@lists•infradead.org
Subject: Compilation problem with drivers/staging/zsmalloc when !SMP on ARM
Date: Fri, 18 Jan 2013 23:37:25 -0500 [thread overview]
Message-ID: <20130119043725.GB5391@phenom.dumpdata.com> (raw)
In-Reply-To: <20130118214527.GA913@kroah.com>
On Fri, Jan 18, 2013 at 01:45:27PM -0800, Greg Kroah-Hartman wrote:
> On Fri, Jan 18, 2013 at 09:08:59PM +0000, Russell King - ARM Linux wrote:
> > On Fri, Jan 18, 2013 at 02:24:15PM -0600, Matt Sealey wrote:
> > > Hello all,
> > >
> > > I wonder if anyone can shed some light on this linking problem I have
> > > right now. If I configure my kernel without SMP support (it is a very
> > > lean config for i.MX51 with device tree support only) I hit this error
> > > on linking:
> >
> > Yes, I looked at this, and I've decided that I will _not_ fix this export,
> > neither will I accept a patch to add an export.
> >
> > As far as I can see, this code is buggy in a SMP environment. There's
> > apparantly no guarantee that:
> >
> > 1. the mapping will be created on a particular CPU.
> > 2. the mapping will then be used only on this specific CPU.
> > 3. no guarantee that another CPU won't speculatively prefetch from this
> > region.
I thought the code had per_cpu for it - so that you wouldn't do that unless
you really went out the way to do it.
> > 4. when the mapping is torn down, no guarantee that it's the same CPU that
> > used the happing.
With per_cpu that actually would be the case.
> >
> > So, the use of the local TLB flush leaves all the other CPUs potentially
> > containing TLB entries for this mapping.
Right. That is the point of a local TLB flush.
> >
> > Finally, there is no TODO file for this driver, which I believe is a
> > requirement for anything to be in stable. So as far as I can see, it
> > should be deleted or a TODO file added. I'm not sure why Greg decided
> > to add it without a TODO file.
A TODO file can certainly be added and it is welcome.
>
> I don't know, I'm cursing the day I took the whole zsmalloc, zcache,
> zram mess that we have in the staging tree now. People are working to
> get them out of staging, which is good, but the churn involved is
> driving me crazy.
Oh oh.
next prev parent reply other threads:[~2013-01-19 4:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-18 20:24 Compilation problem with drivers/staging/zsmalloc when !SMP on ARM Matt Sealey
2013-01-18 21:08 ` Russell King - ARM Linux
2013-01-18 21:45 ` Greg Kroah-Hartman
2013-01-19 4:37 ` Konrad Rzeszutek Wilk [this message]
2013-01-21 15:24 ` Russell King - ARM Linux
2013-01-22 20:33 ` Konrad Rzeszutek Wilk
2013-01-19 1:11 ` Matt Sealey
2013-01-19 4:46 ` Konrad Rzeszutek Wilk
2013-01-21 5:55 ` Minchan Kim
2013-01-21 16:00 ` Matt Sealey
2013-01-22 15:48 ` Minchan Kim
2013-01-22 20:34 ` Konrad Rzeszutek Wilk
2013-01-21 16:20 ` Matt Sealey
2013-01-21 16:29 ` Russell King - ARM Linux
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