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SubjectRe: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t
On 2018-07-03 22:01:38 [+0200], To linux-kernel@vger.kernel.org wrote:
> refcount_t type and corresponding API should be used instead of atomic_t when
> the variable is used as a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free situations.

Andrew, is it okay for you to collect this one (and 4/6 of this series,
both bdi)? The prerequisites are already in Linus' tree.

> Cc: linux-mm@kvack.org
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> include/linux/backing-dev-defs.h | 3 ++-
> include/linux/backing-dev.h | 4 ++--
> mm/backing-dev.c | 12 ++++++------
> 3 files changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
> index 24251762c20c..9a6bc0951cfa 100644
> --- a/include/linux/backing-dev-defs.h
> +++ b/include/linux/backing-dev-defs.h
> @@ -12,6 +12,7 @@
> #include <linux/timer.h>
> #include <linux/workqueue.h>
> #include <linux/kref.h>
> +#include <linux/refcount.h>
>
> struct page;
> struct device;
> @@ -75,7 +76,7 @@ enum wb_reason {
> */
> struct bdi_writeback_congested {
> unsigned long state; /* WB_[a]sync_congested flags */
> - atomic_t refcnt; /* nr of attached wb's and blkg */
> + refcount_t refcnt; /* nr of attached wb's and blkg */
>
> #ifdef CONFIG_CGROUP_WRITEBACK
> struct backing_dev_info *__bdi; /* the associated bdi, set to NULL
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 72ca0f3d39f3..c28a47cbe355 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -404,13 +404,13 @@ static inline bool inode_cgwb_enabled(struct inode *inode)
> static inline struct bdi_writeback_congested *
> wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
> {
> - atomic_inc(&bdi->wb_congested->refcnt);
> + refcount_inc(&bdi->wb_congested->refcnt);
> return bdi->wb_congested;
> }
>
> static inline void wb_congested_put(struct bdi_writeback_congested *congested)
> {
> - if (atomic_dec_and_test(&congested->refcnt))
> + if (refcount_dec_and_test(&congested->refcnt))
> kfree(congested);
> }
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 2e5d3df0853d..55a233d75f39 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -438,10 +438,10 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
> if (new_congested) {
> /* !found and storage for new one already allocated, insert */
> congested = new_congested;
> - new_congested = NULL;
> rb_link_node(&congested->rb_node, parent, node);
> rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree);
> - goto found;
> + spin_unlock_irqrestore(&cgwb_lock, flags);
> + return congested;
> }
>
> spin_unlock_irqrestore(&cgwb_lock, flags);
> @@ -451,13 +451,13 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp)
> if (!new_congested)
> return NULL;
>
> - atomic_set(&new_congested->refcnt, 0);
> + refcount_set(&new_congested->refcnt, 1);
> new_congested->__bdi = bdi;
> new_congested->blkcg_id = blkcg_id;
> goto retry;
>
> found:
> - atomic_inc(&congested->refcnt);
> + refcount_inc(&congested->refcnt);
> spin_unlock_irqrestore(&cgwb_lock, flags);
> kfree(new_congested);
> return congested;
> @@ -474,7 +474,7 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
> unsigned long flags;
>
> local_irq_save(flags);
> - if (!atomic_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
> + if (!refcount_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
> local_irq_restore(flags);
> return;
> }
> @@ -804,7 +804,7 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi)
> if (!bdi->wb_congested)
> return -ENOMEM;
>
> - atomic_set(&bdi->wb_congested->refcnt, 1);
> + refcount_set(&bdi->wb_congested->refcnt, 1);
>
> err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL);
> if (err) {
> --
> 2.18.0

Sebastian

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