On Fri, Feb 17, 2006 at 11:01:26PM +0300, Oleg Nesterov wrote:
> 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.
Looks good to me by inspection, firing off some steamroller tests on it.
Thanx, Paul
> 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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