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.
Suggested-by: Peter Zijlstra <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> --- 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 0bd432a4d7bd..81c75934ca5b 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; @@ -76,7 +77,7 @@ 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 7441bd93b732..7984a872073e 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -450,10 +450,10 @@ 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); @@ -463,13 +463,13 @@ 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; @@ -486,7 +486,7 @@ 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; } @@ -794,7 +794,7 @@ 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) { -- 2.17.0
