From: Peter Zijlstra <peterz@infradead.org>
To: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>,
linux-kernel@vger.kernel.org, Mike Galbraith <efault@gmx.de>,
Arjan van de Ven <arjan@infradead.org>,
Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH 2/9] perf_counter: fix update_userpage()
Date: Thu, 02 Apr 2009 11:28:37 +0200 [thread overview]
Message-ID: <1238664517.8530.5705.camel@twins> (raw)
In-Reply-To: <18900.33695.919419.831813@cargo.ozlabs.ibm.com>
On Thu, 2009-04-02 at 20:21 +1100, Paul Mackerras wrote:
> Peter Zijlstra writes:
>
> > The below might work:
> >
> > u32 seq;
> > s64 count;
> >
> > again:
> > seq = pc->lock;
> >
> > if (unlikely(seq & 1)) {
>
> I don't believe we can ever see this condition, since pc->lock is
> updated in the kernel either at interrupt level on the cpu this task
> is running on, or in the kernel in the context of this task. So this
> userspace code can never run in the middle of the kernel updating
> things.
Colour me paranoid ;-)
next prev parent reply other threads:[~2009-04-02 9:28 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-28 19:43 [PATCH 0/9] perf_counter patches Peter Zijlstra
2009-03-28 19:44 ` [PATCH 1/9] perf_counter: unify and fix delayed counter wakeup Peter Zijlstra
2009-03-29 0:14 ` Paul Mackerras
2009-03-29 9:16 ` Peter Zijlstra
2009-03-29 9:25 ` Peter Zijlstra
2009-03-29 10:02 ` Paul Mackerras
2009-03-28 19:44 ` [PATCH 2/9] perf_counter: fix update_userpage() Peter Zijlstra
2009-03-29 0:24 ` Paul Mackerras
2009-04-02 8:50 ` Peter Zijlstra
2009-04-02 9:00 ` Peter Zijlstra
2009-04-02 9:21 ` Paul Mackerras
2009-04-02 9:28 ` Peter Zijlstra [this message]
2009-04-02 9:15 ` Paul Mackerras
2009-04-02 9:36 ` Peter Zijlstra
2009-04-02 9:58 ` Paul Mackerras
2009-04-02 10:36 ` Peter Zijlstra
2009-03-28 19:44 ` [PATCH 3/9] perf_counter: kerneltop: simplify data_head read Peter Zijlstra
2009-03-28 19:44 ` [PATCH 4/9] perf_counter: executable mmap() information Peter Zijlstra
2009-03-28 19:44 ` [PATCH 5/9] perf_counter: kerneltop: parse the mmap data stream Peter Zijlstra
2009-03-28 19:44 ` [PATCH 6/9] perf_counter: powerpc: only reserve PMU hardware when we need it Peter Zijlstra
2009-03-28 19:44 ` [PATCH 7/9] perf_counter: make it possible for hw_perf_counter_init to return error codes Peter Zijlstra
2009-03-30 4:13 ` Paul Mackerras
2009-03-28 19:44 ` [PATCH 8/9] perf_counter tools: optionally scale counter values in perfstat mode Peter Zijlstra
2009-03-28 19:44 ` [PATCH 9/9] RFC perf_counter: event overlow handling Peter Zijlstra
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=1238664517.8530.5705.camel@twins \
--to=peterz@infradead.org \
--cc=arjan@infradead.org \
--cc=efault@gmx.de \
--cc=fengguang.wu@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=paulus@samba.org \
/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