netdev - Re: [PATCH 1/4][MAC80211]: Fix GFP_KERNEL allocation under read lock.

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Date:	Tue, 6 May 2008 18:40:37 +0200
From:	Ingo Oeser <netdev@...eo.de>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Johannes Berg <johannes@...solutions.net>,
	"John W. Linville" <linville@...driver.com>,
	David Miller <davem@...emloft.net>,
	linux-wireless@...r.kernel.org,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/4][MAC80211]: Fix GFP_KERNEL allocation under read lock.

Hi Pavel,

regarding:

[PATCH 1/4][MAC80211]: Fix GFP_KERNEL allocation under read lock
[PATCH 2/4][MAC80211]: Fix not checked kmalloc() result

Pavel Emelyanov schrieb:
> The mesh_path_add() read-locks the pathtbl_resize_lock and calls
> kmalloc with GFP_KERNEL mask.
> 
> Fix it and move the endadd2 label lower. It should be _before_ the
> if() beyond, but it makes no sense for it being there, so I move it
> right after this if().

What about doing both allocations in succession to local variables,
share the failure path if an error occours an kfree them unconditionally 
like this?

new_node = kmalloc(sizeof(struct mpath_node), GFP_KERNEL);
new_mpath = kzalloc(sizeof(struct mesh_path), GFP_KERNEL);
if (!new_node || !new_mpath) {
	kfree(new_mpath);
	kfree(new_node);
	atomic_dec(&sdata->u.sta.mpaths);
	err = -ENOMEM;
	goto endadd2;
}
...
read_lock(...);
...

Rationale: Allocations are always likely to fail/succeed in close succession.


Best Regards

Ingo Oeser
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