From: Simon Jeons <simon.jeons@gmail.com>
To: Michel Lespinasse <walken@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Rik van Riel <riel@redhat.com>,
Hugh Dickins <hughd@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: protect against concurrent vma expansion
Date: Thu, 03 Jan 2013 19:18:31 -0600 [thread overview]
Message-ID: <1357262311.5105.6.camel@kernel.cn.ibm.com> (raw)
In-Reply-To: <CANN689HQjbXEpWhv5KuaOt2NBEokiOguCXnsum2Bd994zkw6tA@mail.gmail.com>
On Thu, 2013-01-03 at 16:50 -0800, Michel Lespinasse wrote:
> On Thu, Jan 3, 2013 at 4:40 PM, Simon Jeons <simon.jeons@gmail.com> wrote:
> > On Wed, 2012-12-19 at 19:01 -0800, Michel Lespinasse wrote:
> >> Hi Simon,
> >>
> >> On Wed, Dec 19, 2012 at 5:56 PM, Simon Jeons <simon.jeons@gmail.com> wrote:
> >> > One question.
> >> >
> >> > I found that mainly callsite of expand_stack() is #PF, but it holds
> >> > mmap_sem each time before call expand_stack(), how can hold a *shared*
> >> > mmap_sem happen?
> >>
> >> the #PF handler calls down_read(&mm->mmap_sem) before calling expand_stack.
> >>
> >> I think I'm just confusing you with my terminology; shared lock ==
> >> read lock == several readers might hold it at once (I'd say they share
> >> it)
> >
> > Sorry for my late response.
> >
> > Since expand_stack() will modify vma, then why hold a read lock here?
>
> Well, it'd be much nicer if we had a write lock, I think. But, we
> didn't know when taking the lock that we'd end up having to expand
> stacks.
>
> What happens is that page faults don't generally modify vmas, so they
> get a read lock (just to know what vma the fault is happening in) and
> then fault in the page.
>
Thanks for your quick explanation.
> expand_stack() is the one exception to that - after getting the read
> lock as usual, we notice that the fault is not in any vma right now,
> but it's close enough to an expandable vma.
If this senario only occur for userspace stack?
>
--
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:[~2013-01-04 1:18 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-01 6:56 [PATCH] mm: protect against concurrent vma expansion Michel Lespinasse
2012-12-03 23:01 ` Andrew Morton
2012-12-04 0:35 ` Michel Lespinasse
2012-12-04 0:43 ` Andrew Morton
2012-12-04 14:48 ` Michel Lespinasse
2012-12-20 1:56 ` Simon Jeons
2012-12-20 3:01 ` Michel Lespinasse
2013-01-04 0:40 ` Simon Jeons
2013-01-04 0:50 ` Michel Lespinasse
2013-01-04 1:18 ` Simon Jeons [this message]
2013-01-04 2:49 ` Al Viro
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=1357262311.5105.6.camel@kernel.cn.ibm.com \
--to=simon.jeons@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=hughd@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=riel@redhat.com \
--cc=walken@google.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 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).