Re: 2.6.21-rc suspend regression: sysfs deadlock

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Hugh Dickins <hugh@veritas.com>,
	Oliver Neukum <oliver@neukum.name>,
	Maneesh Soni <maneesh@in.ibm.com>,
	Greg Kroah-Hartman <gregkh@suse.de>, Adrian Bunk <bunk@stusta.de>,
	linux-kernel@vger.kernel.org
Subject: Re: 2.6.21-rc suspend regression: sysfs deadlock
Date: Wed, 7 Mar 2007 08:52:18 -0800 (PST)	[thread overview]
Message-ID: <Pine.LNX.4.64.0703070845500.5963@woody.linux-foundation.org> (raw)
In-Reply-To: <d120d5000703070756v4fe11a54u9009d3efd93faa9d@mail.gmail.com>

On Wed, 7 Mar 2007, Dmitry Torokhov wrote:
> 
> ... with the exception that it will again make data associated with
> sysfs attributes accessible past the point of returning from
> sysfs_remove_file. And that was the point so drivers would not have to
> care about handling access to extra data (such as static strings) past
> the driver unload.

Drivers are unloaded by stopping the whole machine (exactly because module 
unload is otherwise so hard to handle), so that never happens unless you 
actively block. In other words, if you do something as simple as

	if (inode->i_private_data)
		sysfs_flush_buffer(buffer);

then there is no race with unloading (unless the driver itself does 
something stupid, of course - but the whole point of having a kernel 
buffer is so that it does *not* have to make user accesses etc).

But the one thing you should *not* do is to depend on a sleeping lock, 
because that breaks the whole model!

			Linus