linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Tejun Heo <tj@kernel.org>
To: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	gregkh@linuxfoundation.org, toshi.kani@hp.com
Subject: Re: [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks
Date: Wed, 23 Apr 2014 10:23:46 -0400	[thread overview]
Message-ID: <20140423142346.GB4781@htj.dyndns.org> (raw)
In-Reply-To: <5356EB6D.3010102@intel.com>

Hello, Rafael.

On Wed, Apr 23, 2014 at 12:21:33AM +0200, Rafael J. Wysocki wrote:
> Can you please elaborate a bit?

Because it can get involved in larger locking dependency issues by
joining dependency graphs of two otherwise largely disjoint
subsystems.  It has potential to create possible deadlocks which don't
need to exist.

> It is there to protect hotplug operations involving multiple devices
> (in different subsystems) from racing with each other.  Why exactly
> is it bad?

But why would different subsystems, say cpu and memory, use the same
lock?  Wouldn't those subsystems already have proper locking inside
their own subsystems?  Why add this additional global lock across
multiple subsystems?

Thanks.

-- 
tejun

  reply	other threads:[~2014-04-23 14:23 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-10  9:18 [RFC PATCH] Suppress a device hot remove related lockdep warning Li Zhong
2014-04-10 13:31 ` Tejun Heo
2014-04-11  4:10   ` [RFC PATCH v2] Use kernfs_break_active_protection() for device online store callbacks Li Zhong
2014-04-11 10:26     ` Tejun Heo
2014-04-14  7:47       ` [RFC PATCH v3] " Li Zhong
2014-04-14 20:13         ` Tejun Heo
2014-04-15  2:44           ` Li Zhong
2014-04-15 14:50             ` Tejun Heo
2014-04-16  1:41               ` Li Zhong
2014-04-16 15:17                 ` Tejun Heo
2014-04-17  3:05                   ` Li Zhong
2014-04-17 15:06                     ` Tejun Heo
2014-04-17  6:50                   ` [RFC PATCH v4] " Li Zhong
2014-04-17 15:17                     ` Tejun Heo
2014-04-18  8:33                       ` Li Zhong
2014-04-21  9:20                       ` [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Li Zhong
2014-04-21  9:23                         ` [RFC PATCH v5 2/2] Use kernfs_break_active_protection() for device online store callbacks Li Zhong
2014-04-21 22:46                           ` Tejun Heo
2014-04-22  3:34                             ` Li Zhong
2014-04-22 10:11                               ` Rafael J. Wysocki
2014-04-23  1:50                                 ` Li Zhong
2014-04-23 10:54                                   ` Rafael J. Wysocki
2014-04-24  1:13                                     ` Li Zhong
2014-04-22 20:44                               ` Tejun Heo
2014-04-22 22:21                                 ` Rafael J. Wysocki
2014-04-23 14:23                                   ` Tejun Heo [this message]
2014-04-23 16:12                                     ` Rafael J. Wysocki
2014-04-23 16:52                                       ` Tejun Heo
2014-04-24  8:59                                       ` Li Zhong
2014-04-24 10:02                                         ` Rafael J. Wysocki
2014-04-25  1:46                                           ` Li Zhong
2014-04-25 12:47                                             ` Rafael J. Wysocki
2014-04-28  1:49                                               ` Li Zhong
2014-04-23  5:03                                 ` Li Zhong
2014-04-23 10:58                                   ` Rafael J. Wysocki
2014-04-24  1:33                                     ` Li Zhong
2014-05-09  8:35                               ` Li Zhong
2014-05-09  8:40                                 ` [RFC PATCH v6 1/2 ] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Li Zhong
2014-05-09  8:40                                   ` [RFC PATCH v6 2/2] Implement lock_device_hotplug_sysfs() by breaking active protection Li Zhong
2014-04-21 22:38                         ` [RFC PATCH v5 1/2] Use lock_device_hotplug() in cpu_probe_store() and cpu_release_store() Tejun Heo
2014-04-22  2:29                           ` Li Zhong
2014-04-22 20:40                             ` Tejun Heo
2014-04-23  2:00                               ` Li Zhong
2014-04-23 14:39                                 ` Tejun Heo
2014-04-24  8:37                                   ` Li Zhong
2014-04-24 14:32                                     ` Tejun Heo
2014-04-25  1:56                                       ` Li Zhong
2014-04-25 12:28                                         ` Tejun Heo
2014-04-28  0:51                                           ` Li Zhong

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=20140423142346.GB4781@htj.dyndns.org \
    --to=tj@kernel.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=rafael.j.wysocki@intel.com \
    --cc=toshi.kani@hp.com \
    --cc=zhong@linux.vnet.ibm.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).