From: Michal Hocko <mhocko@kernel.org>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
Oleg Nesterov <oleg@redhat.com>,
David Rientjes <rientjes@google.com>,
Vladimir Davydov <vdavydov@parallels.com>
Subject: Re: [PATCH 09/10] vhost, mm: make sure that oom_reaper doesn't reap memory read by vhost
Date: Fri, 29 Jul 2016 15:35:29 +0200 [thread overview]
Message-ID: <20160729133529.GE8031@dhcp22.suse.cz> (raw)
In-Reply-To: <20160729161039-mutt-send-email-mst@kernel.org>
On Fri 29-07-16 16:14:10, Michael S. Tsirkin wrote:
> On Fri, Jul 29, 2016 at 08:04:22AM +0200, Michal Hocko wrote:
> > On Thu 28-07-16 23:41:53, Michael S. Tsirkin wrote:
> > > On Thu, Jul 28, 2016 at 09:42:33PM +0200, Michal Hocko wrote:
[...]
> > > > and the reader would hit a page fault
> > > > + * if it stumbled over a reaped memory.
> > >
> > > This last point I don't get. flag read could bypass data read
> > > if that happens data read could happen after unmap
> > > yes it might get a PF but you handle that, correct?
> >
> > The point I've tried to make is that if the reader really page faults
> > then get_user will imply the full barrier already. If get_user didn't
> > page fault then the state of the flag is not really important because
> > the reaper shouldn't have touched it. Does it make more sense now or
> > I've missed your question?
>
> Can task flag read happen before the get_user pagefault?
Do you mean?
get_user_mm()
temp = false <- test_bit(MMF_UNSTABLE, &mm->flags)
ret = __get_user(x, ptr)
#PF
if (!ret && temp) # misses the flag
The code is basically doing
if (!__get_user() && test_bit(MMF_UNSTABLE, &mm->flags))
so test_bit part of the conditional cannot be evaluated before
__get_user() part is done. Compiler cannot reorder two depending
subconditions AFAIK.
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-07-29 13:35 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-28 19:42 [RFC PATCH 0/10] fortify oom killer even more Michal Hocko
2016-07-28 19:42 ` [PATCH 01/10] mm,oom_reaper: Reduce find_lock_task_mm() usage Michal Hocko
2016-07-28 19:42 ` [PATCH 02/10] mm,oom_reaper: Do not attempt to reap a task twice Michal Hocko
2016-07-28 19:42 ` [PATCH 03/10] oom: keep mm of the killed task available Michal Hocko
2016-07-28 19:42 ` [PATCH 04/10] mm, oom: get rid of signal_struct::oom_victims Michal Hocko
2016-07-28 19:42 ` [PATCH 05/10] kernel, oom: fix potential pgd_lock deadlock from __mmdrop Michal Hocko
2016-07-28 19:42 ` [PATCH 06/10] oom, suspend: fix oom_killer_disable vs. pm suspend properly Michal Hocko
2016-07-28 19:42 ` [PATCH 07/10] mm, oom: enforce exit_oom_victim on current task Michal Hocko
2016-07-28 19:42 ` [PATCH 08/10] exit, oom: postpone exit_oom_victim to later Michal Hocko
2016-07-30 8:20 ` Tetsuo Handa
2016-07-31 9:35 ` Michal Hocko
2016-07-31 10:19 ` Michal Hocko
2016-08-01 10:46 ` Tetsuo Handa
2016-08-01 11:33 ` Michal Hocko
2016-08-02 10:32 ` Tetsuo Handa
2016-08-02 11:31 ` Michal Hocko
2016-07-28 19:42 ` [PATCH 09/10] vhost, mm: make sure that oom_reaper doesn't reap memory read by vhost Michal Hocko
2016-07-28 20:41 ` Michael S. Tsirkin
2016-07-29 6:04 ` Michal Hocko
2016-07-29 13:14 ` Michael S. Tsirkin
2016-07-29 13:35 ` Michal Hocko [this message]
2016-07-29 17:57 ` Michael S. Tsirkin
2016-07-31 9:44 ` Michal Hocko
2016-08-12 9:42 ` Michal Hocko
2016-08-12 13:21 ` Oleg Nesterov
2016-08-12 14:41 ` Michal Hocko
2016-08-12 16:05 ` Oleg Nesterov
2016-08-12 15:57 ` Paul E. McKenney
2016-08-12 16:09 ` Oleg Nesterov
2016-08-12 16:26 ` Paul E. McKenney
2016-08-12 16:23 ` Michal Hocko
2016-08-13 0:15 ` Michael S. Tsirkin
2016-08-14 8:41 ` Michal Hocko
2016-08-14 16:57 ` Michael S. Tsirkin
2016-08-14 23:06 ` Michael S. Tsirkin
2016-08-15 9:49 ` Michal Hocko
2016-08-17 16:58 ` Michal Hocko
2016-08-22 13:03 ` Michal Hocko
2016-08-22 21:01 ` Michael S. Tsirkin
2016-08-23 7:55 ` Michal Hocko
2016-08-23 9:06 ` Michal Hocko
2016-08-23 12:54 ` Michael S. Tsirkin
2016-08-24 16:42 ` Michal Hocko
2016-08-12 9:43 ` Michal Hocko
2016-07-29 17:07 ` Oleg Nesterov
2016-07-31 9:11 ` Michal Hocko
2016-07-28 19:42 ` [PATCH 10/10] oom, oom_reaper: allow to reap mm shared by the kthreads Michal Hocko
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=20160729133529.GE8031@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=linux-mm@kvack.org \
--cc=mst@redhat.com \
--cc=oleg@redhat.com \
--cc=penguin-kernel@I-love.SAKURA.ne.jp \
--cc=rientjes@google.com \
--cc=vdavydov@parallels.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.