Message-ID: <20100318200317.GG2423@linux.vnet.ibm.com>
Date:	Thu, 18 Mar 2010 13:03:17 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, dvhltc@...ibm.com, niv@...ibm.com,
	tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, Alexey Dobriyan <adobriyan@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH tip/core/urgent 2/2] rcu: remove INIT_RCU_HEAD,
 RCU_HEAD_INIT, RCU_HEAD

On Thu, Mar 18, 2010 at 03:35:20PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck@...ux.vnet.ibm.com) wrote:
> > From: Alexey Dobriyan <adobriyan@...il.com>
> > 
> > call_rcu() will unconditionally reinitialize RCU head anyway.  New users
> > of these macros constantly appear, so remove them.
> 
> Hrm. So do we have something that checks for double-use of a RCU head at
> the moment ? (using call_rcu() twice on the same head without being
> certain that the first callback have finished its execution).
> 
> I think that hiding rcu head initialization into call_rcu() is one more
> step towards misuses that will silently corrupt rcu head lists. So I
> think we should first add the double-use debugging option before we
> remove the RCU head initializations.

So your thought is to have rcu_do_batch() do something like the
following?

	...

	next = list->next;
	prefetch(next);
	list->next = RCU_HEAD_INIT_PTR;
	func = list->func;
	list->func = RCU_HEAD_INIT_PTR;
	func(list);
	... /* touching anything referenced by "list" is use-after-free. */

Then have __call_rcu() do something like the following before initializing
the ->func and ->next pointers:

	WARN_ON_ONCE(head->next != RCU_HEAD_INIT_PTR ||
		     head->func != RCU_HEAD_INIT_PTR);

And then require that all users of call_rcu() and friends use one of the
RCU_INIT() macros?

Or did you have something else in mind?

							Thanx, Paul

> Thanks,
> 
> Mathieu
> 
> > 
> > Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Acked-by: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> >  Documentation/DocBook/kernel-locking.tmpl   |    8 --------
> >  arch/powerpc/mm/pgtable.c                   |    1 -
> >  block/cfq-iosched.c                         |    1 -
> >  block/genhd.c                               |    1 -
> >  drivers/staging/batman-adv/hard-interface.c |    1 -
> >  fs/file.c                                   |    3 ---
> >  fs/fs-writeback.c                           |    1 -
> >  fs/partitions/check.c                       |    1 -
> >  include/linux/init_task.h                   |    1 -
> >  include/linux/rcupdate.h                    |    6 ------
> >  mm/backing-dev.c                            |    1 -
> >  mm/slob.c                                   |    1 -
> >  security/selinux/avc.c                      |    1 -
> >  security/selinux/netnode.c                  |    2 --
> >  14 files changed, 0 insertions(+), 29 deletions(-)
> > 
> > diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl
> > index 084f6ad..e6cc574 100644
> > --- a/Documentation/DocBook/kernel-locking.tmpl
> > +++ b/Documentation/DocBook/kernel-locking.tmpl
> > @@ -1725,14 +1725,6 @@ the amount of locking which needs to be done.
> >           if (++cache_num > MAX_CACHE_SIZE) {
> >                   struct object *i, *outcast = NULL;
> >                   list_for_each_entry(i, &amp;cache, list) {
> > -@@ -85,6 +94,7 @@
> > -         obj-&gt;popularity = 0;
> > -         atomic_set(&amp;obj-&gt;refcnt, 1); /* The cache holds a reference */
> > -         spin_lock_init(&amp;obj-&gt;lock);
> > -+        INIT_RCU_HEAD(&amp;obj-&gt;rcu);
> > -
> > -         spin_lock_irqsave(&amp;cache_lock, flags);
> > -         __cache_add(obj);
> >  @@ -104,12 +114,11 @@
> >   struct object *cache_find(int id)
> >   {
> > diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> > index 99df697..82e38d1 100644
> > --- a/arch/powerpc/mm/pgtable.c
> > +++ b/arch/powerpc/mm/pgtable.c
> > @@ -91,7 +91,6 @@ static void pte_free_rcu_callback(struct rcu_head *head)
> >  
> >  static void pte_free_submit(struct pte_freelist_batch *batch)
> >  {
> > -	INIT_RCU_HEAD(&batch->rcu);
> >  	call_rcu(&batch->rcu, pte_free_rcu_callback);
> >  }
> >  
> > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> > index dee9d93..caa2100 100644
> > --- a/block/cfq-iosched.c
> > +++ b/block/cfq-iosched.c
> > @@ -3719,7 +3719,6 @@ static void *cfq_init_queue(struct request_queue *q)
> >  	 * second, in order to have larger depth for async operations.
> >  	 */
> >  	cfqd->last_delayed_sync = jiffies - HZ;
> > -	INIT_RCU_HEAD(&cfqd->rcu);
> >  	return cfqd;
> >  }
> >  
> > diff --git a/block/genhd.c b/block/genhd.c
> > index d13ba76..27e85a2 100644
> > --- a/block/genhd.c
> > +++ b/block/genhd.c
> > @@ -987,7 +987,6 @@ int disk_expand_part_tbl(struct gendisk *disk, int partno)
> >  	if (!new_ptbl)
> >  		return -ENOMEM;
> >  
> > -	INIT_RCU_HEAD(&new_ptbl->rcu_head);
> >  	new_ptbl->len = target;
> >  
> >  	for (i = 0; i < len; i++)
> > diff --git a/drivers/staging/batman-adv/hard-interface.c b/drivers/staging/batman-adv/hard-interface.c
> > index befd488..96ea0e5 100644
> > --- a/drivers/staging/batman-adv/hard-interface.c
> > +++ b/drivers/staging/batman-adv/hard-interface.c
> > @@ -301,7 +301,6 @@ int hardif_add_interface(char *dev, int if_num)
> >  	batman_if->if_num = if_num;
> >  	batman_if->dev = dev;
> >  	batman_if->if_active = IF_INACTIVE;
> > -	INIT_RCU_HEAD(&batman_if->rcu);
> >  
> >  	printk(KERN_INFO "batman-adv:Adding interface: %s\n", dev);
> >  	avail_ifs++;
> > diff --git a/fs/file.c b/fs/file.c
> > index 34bb7f7..cccaead 100644
> > --- a/fs/file.c
> > +++ b/fs/file.c
> > @@ -178,7 +178,6 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
> >  	fdt->open_fds = (fd_set *)data;
> >  	data += nr / BITS_PER_BYTE;
> >  	fdt->close_on_exec = (fd_set *)data;
> > -	INIT_RCU_HEAD(&fdt->rcu);
> >  	fdt->next = NULL;
> >  
> >  	return fdt;
> > @@ -312,7 +311,6 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
> >  	new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
> >  	new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
> >  	new_fdt->fd = &newf->fd_array[0];
> > -	INIT_RCU_HEAD(&new_fdt->rcu);
> >  	new_fdt->next = NULL;
> >  
> >  	spin_lock(&oldf->file_lock);
> > @@ -430,7 +428,6 @@ struct files_struct init_files = {
> >  		.fd		= &init_files.fd_array[0],
> >  		.close_on_exec	= (fd_set *)&init_files.close_on_exec_init,
> >  		.open_fds	= (fd_set *)&init_files.open_fds_init,
> > -		.rcu		= RCU_HEAD_INIT,
> >  	},
> >  	.file_lock	= __SPIN_LOCK_UNLOCKED(init_task.file_lock),
> >  };
> > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > index 76fc4d5..a79d6c3 100644
> > --- a/fs/fs-writeback.c
> > +++ b/fs/fs-writeback.c
> > @@ -77,7 +77,6 @@ static inline bool bdi_work_on_stack(struct bdi_work *work)
> >  static inline void bdi_work_init(struct bdi_work *work,
> >  				 struct wb_writeback_args *args)
> >  {
> > -	INIT_RCU_HEAD(&work->rcu_head);
> >  	work->args = *args;
> >  	work->state = WS_USED;
> >  }
> > diff --git a/fs/partitions/check.c b/fs/partitions/check.c
> > index e8865c1..03608a4 100644
> > --- a/fs/partitions/check.c
> > +++ b/fs/partitions/check.c
> > @@ -455,7 +455,6 @@ struct hd_struct *add_partition(struct gendisk *disk, int partno,
> >  	}
> >  
> >  	/* everything is up and running, commence */
> > -	INIT_RCU_HEAD(&p->rcu_head);
> >  	rcu_assign_pointer(ptbl->part[partno], p);
> >  
> >  	/* suppress uevent if the disk supresses it */
> > diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> > index b1ed1cd..7996fc2 100644
> > --- a/include/linux/init_task.h
> > +++ b/include/linux/init_task.h
> > @@ -49,7 +49,6 @@ extern struct group_info init_groups;
> >  		{ .first = &init_task.pids[PIDTYPE_PGID].node },	\
> >  		{ .first = &init_task.pids[PIDTYPE_SID].node },		\
> >  	},								\
> > -	.rcu		= RCU_HEAD_INIT,				\
> >  	.level		= 0,						\
> >  	.numbers	= { {						\
> >  		.nr		= 0,					\
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 872a98e..7dd951e 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -77,12 +77,6 @@ extern void rcu_scheduler_starting(void);
> >  #error "Unknown RCU implementation specified to kernel configuration"
> >  #endif
> >  
> > -#define RCU_HEAD_INIT	{ .next = NULL, .func = NULL }
> > -#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
> > -#define INIT_RCU_HEAD(ptr) do { \
> > -       (ptr)->next = NULL; (ptr)->func = NULL; \
> > -} while (0)
> > -
> >  #ifdef CONFIG_DEBUG_LOCK_ALLOC
> >  
> >  extern struct lockdep_map rcu_lock_map;
> > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > index 0e8ca03..4745647 100644
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -653,7 +653,6 @@ int bdi_init(struct backing_dev_info *bdi)
> >  	bdi->max_ratio = 100;
> >  	bdi->max_prop_frac = PROP_FRAC_BASE;
> >  	spin_lock_init(&bdi->wb_lock);
> > -	INIT_RCU_HEAD(&bdi->rcu_head);
> >  	INIT_LIST_HEAD(&bdi->bdi_list);
> >  	INIT_LIST_HEAD(&bdi->wb_list);
> >  	INIT_LIST_HEAD(&bdi->work_list);
> > diff --git a/mm/slob.c b/mm/slob.c
> > index 837ebd6..6de238d 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -647,7 +647,6 @@ void kmem_cache_free(struct kmem_cache *c, void *b)
> >  	if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
> >  		struct slob_rcu *slob_rcu;
> >  		slob_rcu = b + (c->size - sizeof(struct slob_rcu));
> > -		INIT_RCU_HEAD(&slob_rcu->head);
> >  		slob_rcu->size = c->size;
> >  		call_rcu(&slob_rcu->head, kmem_rcu_free);
> >  	} else {
> > diff --git a/security/selinux/avc.c b/security/selinux/avc.c
> > index 989fef8..bf4e3bc 100644
> > --- a/security/selinux/avc.c
> > +++ b/security/selinux/avc.c
> > @@ -288,7 +288,6 @@ static struct avc_node *avc_alloc_node(void)
> >  	if (!node)
> >  		goto out;
> >  
> > -	INIT_RCU_HEAD(&node->rhead);
> >  	INIT_HLIST_NODE(&node->list);
> >  	avc_cache_stats_incr(allocations);
> >  
> > diff --git a/security/selinux/netnode.c b/security/selinux/netnode.c
> > index 7100072..3dae9ef 100644
> > --- a/security/selinux/netnode.c
> > +++ b/security/selinux/netnode.c
> > @@ -182,8 +182,6 @@ static void sel_netnode_insert(struct sel_netnode *node)
> >  		BUG();
> >  	}
> >  
> > -	INIT_RCU_HEAD(&node->rcu);
> > -
> >  	/* we need to impose a limit on the growth of the hash table so check
> >  	 * this bucket to make sure it is within the specified bounds */
> >  	list_add_rcu(&node->list, &sel_netnode_hash[idx].list);
> > -- 
> > 1.7.0
> > 
> 
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
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