linux-kernel - Re: [PATCH 3/5] staging: vme: add functions for bridge module refcounting

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Message-ID: <4E4E1F89.4070702@ge.com>
Date:	Fri, 19 Aug 2011 09:32:09 +0100
From:	Martyn Welch <martyn.welch@...com>
To:	"Emilio G. Cota" <cota@...ap.org>
CC:	Manohar Vanga <manohar.vanga@...n.ch>, devel@...verdev.osuosl.org,
	gregkh@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] staging: vme: add functions for bridge module	refcounting

On 13/08/11 09:54, Emilio G. Cota wrote:
> On Fri, Aug 12, 2011 at 12:30:49 +0200, Manohar Vanga wrote:
>> This patch adds functions that allow for reference counting
>> bridge modules. The patch introduces the functions
>> 'vme_bridge_get()' and 'vme_bridge_put()'.
> (snip)
>> +int vme_bridge_get(unsigned int bus_id)
> (snip)
>> +void vme_bridge_put(struct vme_bridge *bridge)
> 
> Note the input parameter imbalance; in fact this is serious
> (see my email on patch 5) because _get() needs to acquire
> vme_buses_lock, whereas _put() doesn't. Since a caller with
> bridge has bridge->num, but the opposite doesn't hold (num
> doesn't give you the bridge without acquiring vme_buses_lock),
> it seems reasonable to me to take the bus_id as the input for
> both functions, because the requirements on the caller are lower.
> 

Patch 4 makes changes the struct vme_bridge to struct vme_dev. Looking at the
callers we are then effectively doing:

vme_bridge_get(vme_dev.id)

Then in vme_bridge_get(), looping through all the buses to find the one with
the correct id...

We could just pass in the struct vme_dev to both functions.

Martyn

> But the locking needs to be handled with care, see my reply
> to patch 5.
> 
> 		Emilio
> 
> _______________________________________________
> devel mailing list
> devel@...uxdriverproject.org
> http://driverdev.linuxdriverproject.org/mailman/listinfo/devel

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