From: Oliver Neukum <oneukum@suse.de>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
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: Mon, 12 Mar 2007 09:54:21 +0100 [thread overview]
Message-ID: <200703120954.22038.oneukum@suse.de> (raw)
In-Reply-To: <Pine.LNX.4.44L0.0703101405330.7545-100000@patience.localdomain>
Am Samstag, 10. März 2007 20:19 schrieb Alan Stern:
> On Fri, 9 Mar 2007, Oliver Neukum wrote:
>
> > Am Freitag, 9. März 2007 21:08 schrieb Alan Stern:
> > > After some more thought, I basically agree with what Oliver wrote
> > > originally. sysfs_dirent is indeed the logical place to store the kref
> > > pointer. However it needs to be used during open and release, not during
> >
> > OK.
> >
> > > read, write, and poll. Another point, which Oliver didn't think of, is
> > > that the kref pointer needs to be passed to the driver as an argument in
> > > the show() and store() method calls.
> >
> > Why? What's wrong with simply calling kref_get/put?
>
> It's the same old problem: the race between unbind and sysfs I/O. What
> good does holding a reference to the private data structure do if the
> show/store method gets called after the driver has been unbound from the
> device? dev_get_drvdata() will no longer provide a valid pointer to the
> private data, so the method will have no way to access it. Hence the
> method needs another argument.
It does half the job. You can make sure the driver is not asked to access
freed memory.
It is true that a driver will have to mark that device "disconnected"
and return errors if that device's attributes are referenced, but this can
be done internally.
Yes, this is a bit more complicated.
{rant mode}
Who came up with the idea of making life simpler by adding a code path?
All these problems were already solved for device nodes. Ioctl is ugly, but
at least a known code path.
{rant off}
> (BTW, the sysfs core would actually need more than a kref. It would also
> need a pointer to a release routine -- the kref contains only the atomic
Yes, this is implied.
Regards
Oliver
next prev parent reply other threads:[~2007-03-12 8:54 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
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 [this message]
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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