block: prevent possible io_context->refcount overflow

Currently io_context has an atomic_t(32-bit) as refcount.  In the case of
cfq, for each device against whcih a task does I/O, a reference to the
io_context would be taken.  And when there are multiple process sharing
io_contexts(CLONE_IO) would also have a reference to the same io_context.

Theoretically the possible maximum number of processes sharing the same
io_context + the number of disks/cfq_data referring to the same io_context
can overflow the 32-bit counter on a very high-end machine.

Even though it is an improbable case, let us make it atomic_long_t.

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 012f065..d4ed600 100644 (file)
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -35,9 +35,9 @@ int put_io_context(struct io_context *ioc)
        if (ioc == NULL)
                return 1;
 
-       BUG_ON(atomic_read(&ioc->refcount) == 0);
+       BUG_ON(atomic_long_read(&ioc->refcount) == 0);
 
-       if (atomic_dec_and_test(&ioc->refcount)) {
+       if (atomic_long_dec_and_test(&ioc->refcount)) {
                rcu_read_lock();
                if (ioc->aic && ioc->aic->dtor)
                        ioc->aic->dtor(ioc->aic);
@@ -90,7 +90,7 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
 
        ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
        if (ret) {
-               atomic_set(&ret->refcount, 1);
+               atomic_long_set(&ret->refcount, 1);
                atomic_set(&ret->nr_tasks, 1);
                spin_lock_init(&ret->lock);
                ret->ioprio_changed = 0;
@@ -151,7 +151,7 @@ struct io_context *get_io_context(gfp_t gfp_flags, int node)
                ret = current_io_context(gfp_flags, node);
                if (unlikely(!ret))
                        break;
-       } while (!atomic_inc_not_zero(&ret->refcount));
+       } while (!atomic_long_inc_not_zero(&ret->refcount));
 
        return ret;
 }
@@ -163,8 +163,8 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc)
        struct io_context *dst = *pdst;
 
        if (src) {
-               BUG_ON(atomic_read(&src->refcount) == 0);
-               atomic_inc(&src->refcount);
+               BUG_ON(atomic_long_read(&src->refcount) == 0);
+               atomic_long_inc(&src->refcount);
                put_io_context(dst);
                *pdst = src;
        }

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 99ac430..ef2f72d 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1282,7 +1282,7 @@ static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
        if (!cfqd->active_cic) {
                struct cfq_io_context *cic = RQ_CIC(rq);
 
-               atomic_inc(&cic->ioc->refcount);
+               atomic_long_inc(&cic->ioc->refcount);
                cfqd->active_cic = cic;
        }
 }

diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 08b987b..dd05434 100644 (file)
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -64,7 +64,7 @@ struct cfq_io_context {
  * and kmalloc'ed. These could be shared between processes.
  */
 struct io_context {
-       atomic_t refcount;
+       atomic_long_t refcount;
        atomic_t nr_tasks;
 
        /* all the fields below are protected by this lock */
@@ -91,8 +91,8 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc)
         * if ref count is zero, don't allow sharing (ioc is going away, it's
         * a race).
         */
-       if (ioc && atomic_inc_not_zero(&ioc->refcount)) {
-               atomic_inc(&ioc->nr_tasks);
+       if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
+               atomic_long_inc(&ioc->refcount);
                return ioc;
        }