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

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Date:	Tue, 06 May 2008 21:46:38 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Ingo Oeser <netdev@...eo.de>
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.

Ingo Oeser wrote:
> 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?

I do not quite like doing so. Since this relies on fact that kfree bears
NULL pointers. But if we ever switch from kmalloc to kmem_cache_alloc,
this will result in an oops.

And as far as sharing the error paths are concerned, I make such thing
in the 4th patch in a more classical manner.

> 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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