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    SubjectRe: [PATCH tip/core/urgent 2/2] rcu: remove INIT_RCU_HEAD, RCU_HEAD_INIT, RCU_HEAD
    * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
    > From: Alexey Dobriyan <adobriyan@gmail.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.

    Thanks,

    Mathieu

    >
    > Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
    > Cc: Ingo Molnar <mingo@elte.hu>
    > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: Paul E. McKenney <paulmck@linux.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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