All of lore.kernel.org
 help / color / mirror / Atom feed
From: Peter Hurley <peter@hurleysoftware.com>
To: Tejun Heo <tj@kernel.org>
Cc: laijs@cn.fujitsu.com, linux-kernel@vger.kernel.org,
	Stefan Richter <stefanr@s5r6.in-berlin.de>,
	linux1394-devel@lists.sourceforge.net,
	Chris Boot <bootc@bootc.net>,
	linux-scsi@vger.kernel.org, target-devel@vger.kernel.org
Subject: Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK
Date: Sat, 22 Feb 2014 09:48:55 -0500	[thread overview]
Message-ID: <5308B8D7.3040309@hurleysoftware.com> (raw)
In-Reply-To: <20140222143859.GD12830@htj.dyndns.org>

On 02/22/2014 09:38 AM, Tejun Heo wrote:
> Hey,
>
> On Fri, Feb 21, 2014 at 06:46:24PM -0500, Peter Hurley wrote:
>> It's a long story but the short version is that
>> Documentation/memory-barriers.txt recently was overhauled to reflect
>> what cpus actually do and what the different archs actually
>> deliver.
>>
>> Turns out that unlock + lock is not guaranteed by all archs to be
>> a full barrier. Thus the smb_mb__after_unlock_lock().
>>
>> This is now all spelled out in memory-barriers.txt under the
>> sub-heading "IMPLICIT KERNEL MEMORY BARRIERS".
>
> So, that one is for unlock/lock sequence, not smp_mb__after_unlock().
> Urgh... kinda dislike adding smp_rmb() there as it's one of the
> barriers which translate to something weighty on most, if not all,
> archs.

The ticket lock, which is used on x86 to implement spinlocks, has no
fence at all for the fast path (only the compiler barrier), so even on
x86 there has to be a real barrier.

IOW, there really isn't an arch that can get away without doing this
barrier because it follows an unlock.

Regards,
Peter Hurley


  reply	other threads:[~2014-02-22 14:49 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-20 20:44 [PATCHSET wq/for-3.15] workqueue: remove PREPARE_[DELAYED_]WORK() Tejun Heo
2014-02-20 20:44 ` [PATCH 1/9] wireless/rt2x00: don't use PREPARE_WORK in rt2800usb.c Tejun Heo
2014-03-07 15:26   ` Tejun Heo
2014-02-20 20:44 ` [PATCH 2/9] ps3-vuart: don't use PREPARE_WORK Tejun Heo
2014-02-20 20:44   ` Tejun Heo
2014-02-21 23:19   ` Geoff Levand
2014-02-21 23:19     ` Geoff Levand
2014-02-20 20:44 ` [PATCH 3/9] floppy: don't use PREPARE_[DELAYED_]WORK Tejun Heo
2014-02-21  9:37   ` Jiri Kosina
2014-02-20 20:44 ` [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK Tejun Heo
2014-02-20 20:44   ` Tejun Heo
2014-02-21  1:44   ` Peter Hurley
2014-02-21  1:59     ` Tejun Heo
2014-02-21  2:07       ` Peter Hurley
2014-02-21  2:07         ` Peter Hurley
2014-02-21  2:13         ` Tejun Heo
2014-02-21  5:13           ` Peter Hurley
2014-02-21 10:03             ` Tejun Heo
2014-02-21 12:51               ` Peter Hurley
2014-02-21 12:51                 ` Peter Hurley
2014-02-21 13:06                 ` Tejun Heo
2014-02-21 16:53                   ` Peter Hurley
2014-02-21 16:57                     ` Tejun Heo
2014-02-21 23:01                       ` Peter Hurley
2014-02-21 23:18                         ` Tejun Heo
2014-02-21 23:46                           ` Peter Hurley
2014-02-22 14:38                             ` Tejun Heo
2014-02-22 14:38                               ` Tejun Heo
2014-02-22 14:48                               ` Peter Hurley [this message]
2014-02-22 18:43                         ` James Bottomley
2014-02-22 18:48                           ` Peter Hurley
2014-02-22 18:48                             ` Peter Hurley
2014-02-22 18:52                             ` James Bottomley
2014-02-22 19:03                               ` Peter Hurley
2014-02-22 19:03                                 ` Peter Hurley
2014-02-23  1:23                                 ` memory-barriers.txt again (was Re: [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK) Stefan Richter
2014-02-23 16:37                                   ` Paul E. McKenney
2014-02-23 16:37                                     ` Paul E. McKenney
2014-02-23 20:35                                     ` Peter Hurley
2014-02-23 23:50                                       ` Paul E. McKenney
2014-02-24  0:09                                         ` Peter Hurley
2014-02-24 16:26                                           ` Paul E. McKenney
2014-02-24 16:26                                             ` Paul E. McKenney
2014-02-24  0:32                                         ` Stefan Richter
2014-02-24 16:27                                           ` Paul E. McKenney
2014-02-23 20:05                                 ` [PATCH 4/9] firewire: don't use PREPARE_DELAYED_WORK James Bottomley
2014-02-23 22:32                                   ` Peter Hurley
2014-02-21 20:45   ` Stefan Richter
2014-02-21 20:45     ` Stefan Richter
2014-03-05 21:34     ` Stefan Richter
2014-03-07 15:18       ` Tejun Heo
2014-03-07 15:26   ` [PATCH UPDATED " Tejun Heo
2014-03-07 15:26     ` Tejun Heo
2014-02-20 20:44 ` [PATCH 5/9] usb: " Tejun Heo
2014-02-20 20:59   ` Greg Kroah-Hartman
2014-02-21 15:06     ` Alan Stern
2014-02-21 15:07       ` Tejun Heo
2014-02-22 14:59   ` [PATCH v2 " Tejun Heo
2014-02-22 15:14     ` Alan Stern
2014-02-22 15:20       ` Peter Hurley
2014-02-22 15:37       ` Tejun Heo
2014-02-22 23:03         ` Alan Stern
2014-02-23  4:29           ` Tejun Heo
2014-02-20 20:44 ` [PATCH 6/9] nvme: don't use PREPARE_WORK Tejun Heo
2014-02-20 20:44   ` Tejun Heo
2014-03-07 15:26   ` Tejun Heo
2014-03-07 15:26     ` Tejun Heo
2014-02-20 20:44 ` [PATCH 7/9] afs: " Tejun Heo
2014-03-07 15:27   ` Tejun Heo
2014-02-20 20:44 ` [PATCH 8/9] staging/fwserial: " Tejun Heo
2014-02-21 15:13   ` Peter Hurley
2014-02-20 20:44 ` [PATCH 9/9] workqueue: remove PREPARE_[DELAYED_]WORK() Tejun Heo
2014-03-07 15:27   ` Tejun Heo
2014-02-20 22:00 ` [PATCH 7/9] afs: don't use PREPARE_WORK David Howells
2014-02-20 22:46   ` Tejun Heo

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=5308B8D7.3040309@hurleysoftware.com \
    --to=peter@hurleysoftware.com \
    --cc=bootc@bootc.net \
    --cc=laijs@cn.fujitsu.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-scsi@vger.kernel.org \
    --cc=linux1394-devel@lists.sourceforge.net \
    --cc=stefanr@s5r6.in-berlin.de \
    --cc=target-devel@vger.kernel.org \
    --cc=tj@kernel.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 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.