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[PATCH] convert sighand_cache to use SLAB_DESTROY_BY_RCU

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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>
This commit is contained in:
Oleg Nesterov 2006-03-28 16:11:12 -08:00 committed by Linus Torvalds
parent 1f09f9749c
commit aa1757f90b
4 changed files with 13 additions and 21 deletions
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3
fs/exec.c
View file

@ -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));

8
include/linux/sched.h
View file

@ -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

21
kernel/fork.c
View file

@ -786,14 +786,6 @@ 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;
@ -806,7 +798,6 @@ static inline int copy_sighand(unsigned long clone_flags, struct task_struct * t
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;
@ -1356,11 +1347,21 @@ 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
kernel/signal.c
View file

@ -330,7 +330,7 @@ void __exit_sighand(struct task_struct *tsk)
/* 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)