From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: linuxppc-dev@ozlabs.org, Nick Piggin <npiggin@kernel.dk>
Subject: Re: in_atomic() check in page_cache_get_speculative()
Date: Fri, 08 Oct 2010 12:31:04 +1100 [thread overview]
Message-ID: <1286501464.2463.400.camel@pasglop> (raw)
In-Reply-To: <20101004153753.2cda1abf@udp111988uds.am.freescale.net>
On Mon, 2010-10-04 at 15:37 -0500, Scott Wood wrote:
> [Updated with Nick's current address; previous one bounced]
>
> On Mon, 4 Oct 2010 15:22:59 -0500
> Scott Wood <scottwood@freescale.com> wrote:
>
> > I'm seeing the in_atomic() check in page_cache_get_speculative()
> > (linux/pagemap.h:138) fail when running e500 KVM with .
>
> Sorry, that should finish as "with CONFIG_DEBUG_VM."
>
> > It's coming
> > from get_user_pages_fast(), from KVM's hva_to_pfn(). This is on kvm.git
> > plus a few local patches that should be completely unrelated, but it
> > looks like this code hasn't changed much in a couple years.
> >
> > Interrupts are disabled by get_user_pages_fast(), but apparently
> > preemption was not separately disabled. The comment in
> > page_cache_get_speculative() says that preemption disabling is done by
> > rcu_read_lock(), and that "this function must be called inside the same
> > rcu_read_lock() section as has been used to lookup the page in the
> > pagecache radix-tree (or page table)".
> >
> > Where is this RCU lock supposed to be acquired? I don't see any RCU in
> > arch/powerpc/mm/gup.c. Is it buried in some macro or function call?
> >
Well, we shouldn't need the rcu lock if interrupts are off, at least
that's my understanding...
Cheers,
Ben.
prev parent reply other threads:[~2010-10-08 1:31 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-04 20:22 in_atomic() check in page_cache_get_speculative() Scott Wood
2010-10-04 20:37 ` Scott Wood
2010-10-08 1:31 ` Benjamin Herrenschmidt [this message]
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