[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, 1 insertions, 2 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 9046ad2b0614..950ebd43cdc3 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -768,7 +768,6 @@ no_thread_group:
                 /*
                  * Move our state over to newsighand and switch it in.
                  */
-                spin_lock_init(&newsighand->siglock);
                 atomic_set(&newsighand->count, 1);
                 memcpy(newsighand->action, oldsighand->action,
                        sizeof(newsighand->action));
@@ -785,7 +784,7 @@ no_thread_group:
                 write_unlock_irq(&tasklist_lock);
 
                 if (atomic_dec_and_test(&oldsighand->count))
-                        sighand_free(oldsighand);
+                        kmem_cache_free(sighand_cachep, oldsighand);
         }
 
         BUG_ON(!thread_group_leader(current));