Re: [PATCH RFC] [PATCH] drivers/scsi/ch.c: Remove BKL in ch_open

[Arjan van de Ven]

On Sun, 11 Oct 2009 15:37:09 +0100
Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:

> On Sun, 11 Oct 2009 15:45:16 +0200 (CEST)
> John Kacur <jkacur@xxxxxxxxxx> wrote:
> 
> [linux-scsi cc'd]
> 
> > Locking in ch_open is covered by the spin_lock, it serializes the
> > calls to idr_find and scsi_device_get. The BKL appears redundant to
> > me here.
> 
> I'm not so sure. In fact there are some quite umm interesting
> questions about this code, and some of them are shared with other
> modules too.
> 
> Consider the following sequence
> 
> 		CPU1				CPU2
> 	register_chrdev
> 		ok
> 						open device
> 						takes lock


but open does not take the BKL, so the BKL is not protecting you at
all against this..



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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