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Commit e58dd0de authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Linus Torvalds
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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@linutronix.de


Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: default avatarPeter 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cedc5b6a

include/linux/backing-dev-defs.h

+2 −1
Original line number Diff line number Diff line
@@ -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

include/linux/backing-dev.h

+2 −2
Original line number Diff line number Diff line
@@ -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);

}

mm/backing-dev.c

+6 −6
Original line number Diff line number Diff line
@@ -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) {