From: "Dmitry Torokhov" <dmitry.torokhov@gmail.com>
To: "Oliver Neukum" <oneukum@suse.de>
Cc: "Alan Stern" <stern@rowland.harvard.edu>,
"Maneesh Soni" <maneesh@in.ibm.com>,
gregkh@suse.de, linux-kernel@vger.kernel.org
Subject: Re: refcounting drivers' data structures used in sysfs buffers
Date: Fri, 9 Mar 2007 12:02:14 -0500 [thread overview]
Message-ID: <d120d5000703090902v6ae88c75ibe18ff0de3e5276d@mail.gmail.com> (raw)
In-Reply-To: <200703091745.00169.oneukum@suse.de>
On 3/9/07, Oliver Neukum <oneukum@suse.de> wrote:
> Am Freitag, 9. März 2007 17:32 schrieb Alan Stern:
> > On Fri, 9 Mar 2007, Oliver Neukum wrote:
> >
> > > Am Donnerstag, 8. März 2007 17:02 schrieb Alan Stern:
> > > > On Thu, 8 Mar 2007, Oliver Neukum wrote:
> > > >
> > > > > Hi,
> > > > >
> > > > > after a lightning bolt from high above I've been looking into refcounting
> > > > > the data structures drivers use to provide the data used to refill sysfs
> > > > > buffers. I've come to the following conclusion.
> > > > >
> > > > > 1. struct sysfs_buffer must have a struct kref * and probably a destructor
> > > > > pointer
> > > > > 2. drivers must be able to pass these pointers through an extended
> > > > > device_create_file()
> > > > > 3. Drivers must use refcounting if they want to use attributes
> > > > > 4. read/write/poll must do refcounting
> > > > >
> > > > > I am not sure where to store the pointers. struct sysfs_dirent() looks
> > > > > like the obvious choice. Comments?
> > > >
> > > > Can you explain the reasoning that led to these conclusions? And what
> > > > exactly was your lightning bolt?
> > >
> > > The old race between disconnect and IO to attribute via sysfs again.
> > > If I cannot disassociate the drivers from the buffers in the buffers, drivers
> > > must not deallocate the data necessary to answer sysfs callbacks while
> > > a buffer exists.
> >
> > Why wouldn't you be able to dissociate a driver from a buffer? That was
> > the whole point of adding .orphan to sysfs_buffer and creating
> > sysfs_buffer_collection -- it was supposed to solve exactly this race.
>
> It did solve the race but deadlocked when unbinding devices through sysfs.
> Linux therefore asked for the patch to be reverted and wants the isue solved
> with refcounting.
>
I think we already have all refcounting that is needed. What is
missing is subsystem-provided ->release() hooks for drivers to release
driver-specific resources when a device finally goes away.
--
Dmitry
next prev parent reply other threads:[~2007-03-09 17:02 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-08 13:05 refcounting drivers' data structures used in sysfs buffers Oliver Neukum
2007-03-08 16:02 ` Alan Stern
2007-03-09 0:45 ` Oliver Neukum
2007-03-09 16:32 ` Alan Stern
2007-03-09 16:44 ` Oliver Neukum
2007-03-09 17:02 ` Dmitry Torokhov [this message]
2007-03-09 17:18 ` Oliver Neukum
2007-03-09 17:34 ` Dmitry Torokhov
2007-03-09 19:32 ` Alan Stern
2007-03-09 20:05 ` Oliver Neukum
2007-03-09 20:27 ` Alan Stern
2007-03-09 20:39 ` Oliver Neukum
2007-03-09 20:08 ` Alan Stern
2007-03-09 20:48 ` Oliver Neukum
2007-03-10 19:19 ` Alan Stern
2007-03-12 8:54 ` Oliver Neukum
2007-03-12 14:57 ` Alan Stern
2007-03-12 15:23 ` Oliver Neukum
2007-03-12 15:42 ` Dmitry Torokhov
2007-03-12 15:59 ` Oliver Neukum
2007-03-12 16:21 ` Alan Stern
2007-03-12 18:25 ` Oliver Neukum
2007-03-12 19:31 ` Alan Stern
2007-03-12 19:49 ` Oliver Neukum
2007-03-12 20:03 ` Alan Stern
2007-03-12 20:15 ` Oliver Neukum
2007-03-12 20:31 ` Dmitry Torokhov
2007-03-12 20:45 ` Alan Stern
2007-03-12 21:31 ` Richard Purdie
2007-03-13 15:00 ` 2.6.21-rc suspend regression: sysfs deadlock Alan Stern
2007-03-13 18:42 ` Cornelia Huck
2007-03-13 21:20 ` Linus Torvalds
2007-03-14 16:12 ` Alan Stern
2007-03-14 18:43 ` Cornelia Huck
2007-03-14 19:23 ` Alan Stern
2007-03-15 10:27 ` Cornelia Huck
2007-03-15 12:31 ` Hugh Dickins
2007-03-15 13:02 ` Oliver Neukum
2007-03-15 13:22 ` Dmitry Torokhov
2007-03-15 13:59 ` Hugh Dickins
2007-03-15 14:27 ` Alan Stern
2007-03-15 15:32 ` Cornelia Huck
2007-03-15 16:29 ` Hugh Dickins
2007-03-15 16:51 ` Linus Torvalds
2007-03-15 19:50 ` [PATCH] sysfs and driver core: add callback helper, used by SCSI and S390 Alan Stern
2007-03-15 19:51 ` [PATCH] sysfs: reinstate exclusion between method calls and attribute unregistration Alan Stern
2007-03-13 19:00 ` 2.6.21-rc suspend regression: sysfs deadlock Hugh Dickins
2007-03-13 20:09 ` Alan Stern
2007-03-13 20:55 ` Hugh Dickins
2007-03-13 21:08 ` Dmitry Torokhov
2007-03-13 21:20 ` Alan Stern
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