LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andrea Arcangeli <andrea@qumranet.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <clameter@sgi.com>,
	Jack Steiner <steiner@sgi.com>, Nick Piggin <npiggin@suse.de>,
	akpm@linux-foundation.org, Robin Holt <holt@sgi.com>,
	Avi Kivity <avi@qumranet.com>,
	kvm-devel@lists.sourceforge.net, general@lists.openfabrics.org,
	Steve Wise <swise@opengridcomputing.com>,
	Roland Dreier <rdreier@cisco.com>,
	Kanoj Sarcar <kanojsarcar@yahoo.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	daniel.blueman@quadrics.com
Subject: Re: [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier methods to sleep (#v9 was 1/4)
Date: Fri, 7 Mar 2008 18:50:19 +0100	[thread overview]
Message-ID: <20080307175019.GK24114@v2.random> (raw)
In-Reply-To: <1204908762.8514.114.camel@twins>

On Fri, Mar 07, 2008 at 05:52:42PM +0100, Peter Zijlstra wrote:
> hlist_del_rcu(&mn->hlist)
> 
> > +			rcu_read_unlock();
> 
> kfree(mn);
> 
> >  			young |= mn->ops->clear_flush_young(mn, mm, address);
> 
> *BANG*

My objective was to allow mmu_notifier_register/unregister to be
called with the same mmu notifier object, I didn't mean the object
could have been freed until ->release is called. However you reminded
me that after unregistering ->release won't be called so unregister
isn't very useful and I doubt we can keep it ;).

In the meantime I've also been thinking that we could need the
write_seqlock in mmu_notifier_register, to know when to restart the
loop if somebody does a mmu_notifier_register;
synchronize_rcu(). Otherwise there's no way to be sure the mmu
notifier will start firing immediately after synchronize_rcu. I'm
unsure if it's acceptable that in-progress mmu notifier invocations,
don't need to notice the fact that somebody did mmu_notifier_register;
synchronize_rcu. If they don't need to notice, then we can just drop
unregister and all rcu_read_lock()s instead of adding write_seqlock to
the register operation.

Overall my effort is to try to avoid expand the list walk with
explicit memory barriers like in EMM while trying to be equally
efficient.

Another issue is that the _begin/_end logic doesn't provide any
guarantee that the _begin will start firing before _end, if a kernel
module is loaded while another cpu is already running inside some
munmap operation etc.. The KVM usage of mmu notifier has no problem
with that detail, but KVM doesn't use _begin at all, I wonder if
others would have problems. This is a kind of a separate problem, but
quite related to the question if the notifiers must be guaranteed to
start firing immediately after mmu_notifier_unregister;synchronize_rcu
or not, that's why I mentioned it here.

Once I get comments on the suggested direction for these details, I'll
quickly repost a replacement patch for 3/4.

Thanks Peter!

  reply	other threads:[~2008-03-07 17:50 UTC|newest]

Thread overview: 115+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-19  8:43 [patch] my mmu notifiers Nick Piggin
2008-02-19  8:44 ` [patch] my mmu notifier sample driver Nick Piggin
2008-02-19 11:59 ` [patch] my mmu notifiers Robin Holt
2008-02-19 13:58 ` Andrea Arcangeli
2008-02-19 14:27   ` Jack Steiner
2008-02-19 23:04     ` Nick Piggin
2008-02-20  0:52       ` Andrea Arcangeli
2008-02-20  2:46         ` Robin Holt
2008-02-27 22:50     ` Christoph Lameter
2008-02-19 22:59   ` Nick Piggin
2008-02-20  0:46     ` Andrea Arcangeli
2008-02-27 22:55     ` Christoph Lameter
2008-02-19 23:11   ` Nick Piggin
2008-02-19 23:40     ` Jack Steiner
2008-02-21  4:42       ` Nick Piggin
2008-02-22 16:31         ` Jack Steiner
2008-02-20  1:09     ` Andrea Arcangeli
2008-02-20 10:39       ` [PATCH] mmu notifiers #v6 Andrea Arcangeli
2008-02-20 10:45         ` [PATCH] KVM swapping (+ seqlock fix) with " Andrea Arcangeli
2008-02-27 22:06           ` [PATCH] KVM swapping with mmu notifiers #v7 Andrea Arcangeli
2008-02-28  8:42             ` izik eidus
2008-02-20 11:33         ` [PATCH] mmu notifiers #v6 Robin Holt
2008-02-20 12:03           ` Andrea Arcangeli
2008-02-20 12:24             ` Robin Holt
2008-02-20 12:32               ` Andrea Arcangeli
2008-02-20 13:15                 ` Robin Holt
2008-02-21  5:02             ` Nick Piggin
2008-02-20 14:41         ` Robin Holt
2008-02-20 15:34           ` Andrea Arcangeli
2008-02-20 21:03         ` Jack Steiner
2008-02-21  4:54         ` Nick Piggin
2008-02-21 14:40           ` Andrea Arcangeli
2008-02-21 16:10             ` Jack Steiner
2008-02-27 19:26               ` [PATCH] mmu notifiers #v7 Andrea Arcangeli
2008-02-27 20:04                 ` Peter Zijlstra
2008-02-27 23:06                 ` Christoph Lameter
2008-02-27 23:43                   ` [kvm-devel] " Andrea Arcangeli
2008-02-28  0:08                     ` Christoph Lameter
2008-02-28  0:21                       ` Andrea Arcangeli
2008-02-28  0:24                         ` Christoph Lameter
2008-02-28 19:48                 ` Christoph Lameter
2008-02-28 21:52                   ` Andrea Arcangeli
2008-02-28 22:00                     ` Christoph Lameter
2008-02-28 23:17                     ` Jack Steiner
2008-02-29  0:24                       ` Andrea Arcangeli
2008-02-29  1:13                         ` Christoph Lameter
2008-02-28 23:05                 ` Christoph Lameter
2008-02-29  0:40                   ` Andrea Arcangeli
2008-02-29  0:56                     ` Andrew Morton
2008-02-29  1:03                     ` Christoph Lameter
2008-02-29 13:09                       ` Andrea Arcangeli
2008-02-29 19:46                         ` Christoph Lameter
2008-03-02 15:54                 ` [PATCH] mmu notifiers #v8 Andrea Arcangeli
2008-03-02 16:03                   ` [PATCH] mmu notifiers #v8 + xpmem Andrea Arcangeli
2008-03-02 16:23                     ` Peter Zijlstra
2008-03-03  3:29                   ` [PATCH] mmu notifiers #v8 Nick Piggin
2008-03-03 12:51                     ` Andrea Arcangeli
2008-03-03 13:10                       ` Nick Piggin
2008-03-03 13:24                         ` Andrea Arcangeli
2008-03-03 15:18                         ` Jack Steiner
2008-03-03 16:59                           ` Nick Piggin
2008-03-03 18:06                             ` Jack Steiner
2008-03-03 18:09                               ` Avi Kivity
2008-03-03 18:23                                 ` Jack Steiner
2008-03-03 18:45                               ` Nick Piggin
2008-03-03 19:15                                 ` Jack Steiner
2008-03-04 10:35                                   ` Peter Zijlstra
2008-03-04 14:44                                     ` Jack Steiner
2008-03-03 19:02                             ` Christoph Lameter
2008-03-03 19:01                     ` Christoph Lameter
2008-03-03 21:15                       ` Andrea Arcangeli
2008-03-05  0:37                       ` Nick Piggin
2008-03-05 18:48                         ` Christoph Lameter
2008-03-06  2:59                           ` Nick Piggin
2008-03-03  3:33                   ` Nick Piggin
2008-03-03 19:03                     ` Christoph Lameter
2008-03-03  3:34                   ` Nick Piggin
2008-03-03 19:04                     ` Christoph Lameter
2008-03-03  3:39                   ` Nick Piggin
2008-03-03 21:37                   ` [PATCH] mmu notifiers #v9 Andrea Arcangeli
2008-03-03 22:05                     ` [PATCH] KVM swapping with " Andrea Arcangeli
2008-03-04  0:44                       ` izik eidus
2008-03-04  7:31                         ` [RFC] Notifier for Externally Mapped Memory (EMM) Christoph Lameter
2008-03-04  7:34                           ` [Early draft] Conversion of i_mmap_lock to semaphore Christoph Lameter
2008-03-04 13:30                           ` [RFC] Notifier for Externally Mapped Memory (EMM) Andrea Arcangeli
2008-03-04 19:00                             ` Christoph Lameter
2008-03-04 22:20                               ` Andrea Arcangeli
2008-03-04 22:35                                 ` Christoph Lameter
2008-03-04 22:42                                   ` Peter Zijlstra
2008-03-04 23:14                                     ` Christoph Lameter
2008-03-04 23:25                                       ` Peter Zijlstra
2008-03-04 23:30                                         ` Peter Zijlstra
2008-03-05  5:09                                     ` Avi Kivity
2008-03-05  9:47                                       ` Robin Holt
2008-03-05  9:53                                         ` Avi Kivity
2008-03-05 10:02                                         ` [kvm-devel] " Dor Laor
2008-03-07 15:17                                   ` [PATCH] 2/4 move all invalidate_page outside of PT lock (#v9 was 1/4) Andrea Arcangeli
2008-03-07 15:23                                     ` [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier methods to sleep " Andrea Arcangeli
2008-03-07 15:52                                       ` [PATCH] 4/4 i_mmap_lock spinlock2rwsem " Andrea Arcangeli
2008-03-07 20:03                                         ` Christoph Lameter
2008-03-19 21:27                                         ` Christoph Lameter
2008-03-07 16:52                                       ` [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier methods to sleep " Peter Zijlstra
2008-03-07 17:50                                         ` Andrea Arcangeli [this message]
2008-03-07 18:01                                           ` Peter Zijlstra
2008-03-07 18:45                                             ` Andrea Arcangeli
2008-03-07 19:47                                               ` Andrea Arcangeli
2008-03-07 20:15                                                 ` Christoph Lameter
2008-03-07 20:12                                               ` Christoph Lameter
2008-03-07 20:10                                           ` Christoph Lameter
2008-03-07 20:00                                       ` Christoph Lameter
2008-03-07 19:54                                     ` [PATCH] 2/4 move all invalidate_page outside of PT lock " Christoph Lameter
2008-03-04 13:21                         ` [PATCH] KVM swapping with mmu notifiers #v9 Andrea Arcangeli
2008-02-21  4:47       ` [patch] my mmu notifiers Nick Piggin
2008-02-20  2:49     ` Robin Holt
2008-02-27 22:56     ` Christoph Lameter

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20080307175019.GK24114@v2.random \
    --to=andrea@qumranet.com \
    --cc=a.p.zijlstra@chello.nl \
    --cc=akpm@linux-foundation.org \
    --cc=avi@qumranet.com \
    --cc=clameter@sgi.com \
    --cc=daniel.blueman@quadrics.com \
    --cc=general@lists.openfabrics.org \
    --cc=holt@sgi.com \
    --cc=kanojsarcar@yahoo.com \
    --cc=kvm-devel@lists.sourceforge.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=npiggin@suse.de \
    --cc=rdreier@cisco.com \
    --cc=steiner@sgi.com \
    --cc=swise@opengridcomputing.com \
    --subject='Re: [PATCH] 3/4 combine RCU with seqlock to allow mmu notifier methods to sleep (#v9 was 1/4)' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).