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bdi: use refcount_t for reference counting instead atomic_t

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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@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Sebastian Andrzej Siewior 2018-08-21 21:55:31 -07:00 committed by Linus Torvalds
parent cedc5b6aab
commit e58dd0de5e
3 changed files with 10 additions and 9 deletions
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3
include/linux/backing-dev-defs.h
View file

@ -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

4
include/linux/backing-dev.h
View file

@ -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);
}

12
mm/backing-dev.c
View file

@ -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) {