From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Subject: bdi: use refcount_t for reference counting instead atomic_t refcount_t type and corresponding API should be used instead of atomic_t when the variable is used as a reference counter. This permits avoiding accidental refcounter overflows that might lead to use-after-free situations. Link: http://lkml.kernel.org/r/20180703200141.28415-4-bigeasy@xxxxxxxxxxxxx Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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(-) --- a/include/linux/backing-dev-defs.h~bdi-use-refcount_t-for-reference-counting-instead-atomic_t +++ a/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 --- a/include/linux/backing-dev.h~bdi-use-refcount_t-for-reference-counting-instead-atomic_t +++ a/include/linux/backing-dev.h @@ -404,13 +404,13 @@ static inline bool inode_cgwb_enabled(st 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); } --- a/mm/backing-dev.c~bdi-use-refcount_t-for-reference-counting-instead-atomic_t +++ a/mm/backing-dev.c @@ -473,10 +473,10 @@ retry: 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); @@ -486,13 +486,13 @@ retry: 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; @@ -509,7 +509,7 @@ void wb_congested_put(struct bdi_writeba 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; } @@ -839,7 +839,7 @@ static int cgwb_bdi_init(struct backing_ 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) { _
