Messages in this thread Patch in this message | | | Date | Fri, 17 Feb 2006 23:01:26 +0300 | From | Oleg Nesterov <> | Subject | [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.
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 <oleg@tv-sign.ru>
--- 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)); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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