linux-kernel - Sysfs attributes racing with unregistration

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Date:	Wed, 4 Jan 2012 11:52:20 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <tj@...nel.org>
cc:	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Sysfs attributes racing with unregistration

Tejun:

Can you explain the current situation regarding access to sysfs
attributes and possible races with kobject removal?  I have two
questions in particular:

	What happens if one thread calls an attribute's show or
	store method concurrently with another thread unregistering
	the underlying kobject?

	What happens if a thread continues to hold an open fd 
	reference to a sysfs attribute file after the kobject is
	unregistered, and then tries to read or write that fd?

If there are any guarantees about what happens in these situations, I 
can't find them in the kernel source.

And of course, if you can think of any other matters related to this 
topic, please mention them.

Alan Stern

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