linux-kernel - Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories.

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Date:	Thu, 28 May 2009 13:51:39 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Hannes Reinecke <hare@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	<linux-fsdevel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs  directories.

On Thu, 28 May 2009, Eric W. Biederman wrote:

> Alan Stern <stern@...land.harvard.edu> writes:
> 
> > There's another point to consider.  If you do accept my argument that 
> > empty targets can be removed from visibility regardless of the host's 
> > state, then this removal races with addition of a new child.  Since 
> > removal involves calling device_del(), it can't be protected by the 
> > host lock.  Instead we'd have to use a mutex to protect both target 
> > addition and target removal.
> 
> Careful.  Holding a lock over device_del is an easy and hidden way
> to trigger a rare deadlocks.

Your point is well taken.  In addition, I don't really like the idea of 
forcing device removal to wait for some other device to be added.

I'll work around the problem somehow...  A short polling loop shoud do 
the job.

Alan Stern

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