Re: [PATCH 2/2] mac80211: Fixing Races for skipping tailroom reservation

[Yogesh Ashok Powar <yogeshp@marvell.com>]

On Wed, Jun 22, 2011 at 05:49:25AM -0700, Johannes Berg wrote:
> On Wed, 2011-06-22 at 18:01 +0530, Yogesh Ashok Powar wrote:
> > > Will work on some other logic.
> > 
> > Following is the complete V2-patch
> > 
> > v2 changes: a) Moved counter++ before __ieee80211_key_replace in
> > 		key_link()
> > 	    b) Moved crypto_tx_tailroom_needed_cnt to sdata resolve
> > 	        issue with multiple sdata instances in hw reset.
> 
> Looks good. Now I'm just worried about memory and compiler barriers that
> may be needed so the counter update doesn't move after anything else...
> Hmm.

I some how feel that synchronize_net may be replaced with
synchronize_rcu and still the race wont happen.

So the new logic would be 
- counter++		<-- Here keys are not added or deleted
			    so rcu readers wont have problem
			    with extra space allocated.

- synchronize_rcu	<-- This will flush existing readers. Again
			    new readers will have no problem with extra
			    space allocated.

Let me know your opinion on this.

Thanks
Yogesh