[PATCH] convert sighand_cache to use SLAB_DESTROY_BY_RCU

This patch borrows a clever Hugh's 'struct anon_vma' trick.

Without tasklist_lock held we can't trust task->sighand until we locked it
and re-checked that it is still the same.

But this means we don't need to defer 'kmem_cache_free(sighand)'.  We can
return the memory to slab immediately, all we need is to be sure that
sighand->siglock can't dissapear inside rcu protected section.

To do so we need to initialize ->siglock inside ctor function,
SLAB_DESTROY_BY_RCU does the rest.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 0 insertions, 8 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ddc0df7f8bf5..bbcfc873bd98 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -355,16 +355,8 @@ struct sighand_struct {
 	atomic_t		count;
 	struct k_sigaction	action[_NSIG];
 	spinlock_t		siglock;
-	struct rcu_head		rcu;
 };
 
-extern void sighand_free_cb(struct rcu_head *rhp);
-
-static inline void sighand_free(struct sighand_struct *sp)
-{
-	call_rcu(&sp->rcu, sighand_free_cb);
-}
-
 /*
  * NOTE! "signal_struct" does not have it's own
  * locking, because a shared signal_struct always