Re: [B.A.T.M.A.N.] [PATCH 2/2] batman-adv: Fix general protection fault in batadv_tt_global_del_orig()

[Antonio Quartulli <ordex@autistici.org>]

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On Sun, Mar 17, 2013 at 05:44:58AM +0100, Linus Lüssing wrote:
> On shutdown a race condition where we access a just freed global TT hash
> might occure. batadv_orig_node_free_rcu() callbacks might have been
> scheduled (especially during the shutdown procedure) and unfortunately
> batadv_tt_global_table_free() does not wait for them to finish first
> before freeing the global TT hash.
> 
> This potentially results in a general protection fault in
> batadv_tt_global_del_orig(), called via a batadv_orig_node_free_rcu()
> callback, which tries to access the just freed global TT hash.
> 
> This patch tries to fix this by waiting for any just scheduled
> batadv_orig_node_free_rcu() to finish via an extra rcu_barrier() call
> before freeing the global TT hash. And by moving the TT freeing call to
> the end of the batman cleanup routines.
> 
> Signed-off-by: Linus Lüssing <linus.luessing@web.de>

Acked-by: Antonio Quartulli <ordex@autistici.org>

@Marek: when you will merge this commit, can you please reword "tries to fix" in
"fixes" ? :)
Actually this patch is fixing the problem :)

However, as I discussed with Linus on IRC, this is only a temporary fix, which
aims to remove the problem, but still we will need a redesign of the TT clean up
routine in order to cleanly get rid of this race condition.

Cheers,



-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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