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.
include/linux/sched.h | 8 --------
kernel/fork.c | 21 +++++++++++----------
kernel/signal.c | 2 +-
fs/exec.c | 3 +--
4 files changed, 13 insertions(+), 21 deletions(-)
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.16-rc3/include/linux/sched.h~1_DBR 2006-02-16 22:04:46.000000000 +0300
+++ 2.6.16-rc3/include/linux/sched.h 2006-02-18 00:05:20.000000000 +0300
@@ -353,16 +353,8 @@ 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
--- 2.6.16-rc3/kernel/fork.c~1_DBR 2006-02-16 23:15:23.000000000 +0300
+++ 2.6.16-rc3/kernel/fork.c 2006-02-18 01:11:59.000000000 +0300
@@ -784,14 +784,6 @@ int unshare_files(void)
EXPORT_SYMBOL(unshare_files);
-void sighand_free_cb(struct rcu_head *rhp)
-{
- struct sighand_struct *sp;
-
- sp = container_of(rhp, struct sighand_struct, rcu);
- kmem_cache_free(sighand_cachep, sp);
-}
-
static inline int copy_sighand(unsigned long clone_flags, struct task_struct * tsk)
{
struct sighand_struct *sig;
@@ -804,7 +796,6 @@ static inline int copy_sighand(unsigned
rcu_assign_pointer(tsk->sighand, sig);
if (!sig)
return -ENOMEM;
- spin_lock_init(&sig->siglock);
atomic_set(&sig->count, 1);
memcpy(sig->action, current->sighand->action, sizeof(sig->action));
return 0;
@@ -1345,11 +1336,21 @@ long do_fork(unsigned long clone_flags,
#define ARCH_MIN_MMSTRUCT_ALIGN 0
#endif
+static void sighand_ctor(void *data, kmem_cache_t *cachep, unsigned long flags)
+{
+ struct sighand_struct *sighand = data;
+
+ if ((flags & (SLAB_CTOR_VERIFY | SLAB_CTOR_CONSTRUCTOR)) ==
+ SLAB_CTOR_CONSTRUCTOR)
+ spin_lock_init(&sighand->siglock);
+}
+
void __init proc_caches_init(void)
{
sighand_cachep = kmem_cache_create("sighand_cache",
sizeof(struct sighand_struct), 0,
- SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
+ SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_DESTROY_BY_RCU,
+ sighand_ctor, NULL);
signal_cachep = kmem_cache_create("signal_cache",
sizeof(struct signal_struct), 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
--- 2.6.16-rc3/kernel/signal.c~1_DBR 2006-02-13 21:47:19.000000000 +0300
+++ 2.6.16-rc3/kernel/signal.c 2006-02-18 00:07:37.000000000 +0300
@@ -330,7 +330,7 @@ void __exit_sighand(struct task_struct *
/* Ok, we're done with the signal handlers */
tsk->sighand = NULL;
if (atomic_dec_and_test(&sighand->count))
- sighand_free(sighand);
+ kmem_cache_free(sighand_cachep, sighand);
}
void exit_sighand(struct task_struct *tsk)
--- 2.6.16-rc3/fs/exec.c~1_DBR 2006-02-16 22:34:59.000000000 +0300
+++ 2.6.16-rc3/fs/exec.c 2006-02-18 01:12:36.000000000 +0300
@@ -751,7 +751,6 @@ 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));
@@ -768,7 +767,7 @@ 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));
-
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