[PATCH 0/5] v3 block subsystem refcounter conversions

[PATCH 0/5] v3 block subsystem refcounter conversions

[Elena Reshetova]

Changes in v3:
No changes in patches apart from trivial rebases, but now by
default refcount_t = atomic_t and uses all atomic standard operations
unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
systems that are critical on performance and cannot accept even
slight delay on the refcounter operations.

Changes in v2:
Not needed WARNs are removed since refcount_t warns by itself.
BUG_ONs are left as it is, since refcount_t doesn't bug by default.

This series, for block subsystem, replaces atomic_t reference
counters with the new refcount_t type and API (see include/linux/refcount.h).
By doing this we prevent intentional or accidental
underflows or overflows that can lead to use-after-free vulnerabilities.

Elena Reshetova (5):
  block: convert bio.__bi_cnt from atomic_t to refcount_t
  block: convert blk_queue_tag.refcnt from atomic_t to refcount_t
  block: convert blkcg_gq.refcnt from atomic_t to refcount_t
  block: convert io_context.active_ref from atomic_t to refcount_t
  block: convert bsg_device.ref_count from atomic_t to refcount_t

 block/bfq-iosched.c        | 2 +-
 block/bio.c                | 6 +++---
 block/blk-cgroup.c         | 2 +-
 block/blk-ioc.c            | 4 ++--
 block/blk-tag.c            | 8 ++++----
 block/bsg.c                | 9 +++++----
 block/cfq-iosched.c        | 4 ++--
 fs/btrfs/volumes.c         | 2 +-
 include/linux/bio.h        | 4 ++--
 include/linux/blk-cgroup.h | 9 ++++-----
 include/linux/blk_types.h  | 3 ++-
 include/linux/blkdev.h     | 3 ++-
 include/linux/iocontext.h  | 6 +++---
 13 files changed, 32 insertions(+), 30 deletions(-)

-- 
2.7.4

[PATCH 1/5] block: convert bio.__bi_cnt from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 block/bio.c               | 6 +++---
 fs/btrfs/volumes.c        | 2 +-
 include/linux/bio.h       | 4 ++--
 include/linux/blk_types.h | 3 ++-
 4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 888e780..80032f3 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -276,7 +276,7 @@ void bio_init(struct bio *bio, struct bio_vec *table,
 {
 	memset(bio, 0, sizeof(*bio));
 	atomic_set(&bio->__bi_remaining, 1);
-	atomic_set(&bio->__bi_cnt, 1);
+	refcount_set(&bio->__bi_cnt, 1);
 
 	bio->bi_io_vec = table;
 	bio->bi_max_vecs = max_vecs;
@@ -551,12 +551,12 @@ void bio_put(struct bio *bio)
 	if (!bio_flagged(bio, BIO_REFFED))
 		bio_free(bio);
 	else {
-		BIO_BUG_ON(!atomic_read(&bio->__bi_cnt));
+		BIO_BUG_ON(!refcount_read(&bio->__bi_cnt));
 
 		/*
 		 * last put frees it
 		 */
-		if (atomic_dec_and_test(&bio->__bi_cnt))
+		if (refcount_dec_and_test(&bio->__bi_cnt))
 			bio_free(bio);
 	}
 }
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 017b67d..cd8a5d5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -446,7 +446,7 @@ static noinline void run_scheduled_bios(struct btrfs_device *device)
 		    waitqueue_active(&fs_info->async_submit_wait))
 			wake_up(&fs_info->async_submit_wait);
 
-		BUG_ON(atomic_read(&cur->__bi_cnt) == 0);
+		BUG_ON(refcount_read(&cur->__bi_cnt) == 0);
 
 		/*
 		 * if we're doing the sync list, record that our
diff --git a/include/linux/bio.h b/include/linux/bio.h
index d1b04b0..bfd0661 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -229,7 +229,7 @@ static inline void bio_get(struct bio *bio)
 {
 	bio->bi_flags |= (1 << BIO_REFFED);
 	smp_mb__before_atomic();
-	atomic_inc(&bio->__bi_cnt);
+	refcount_inc(&bio->__bi_cnt);
 }
 
 static inline void bio_cnt_set(struct bio *bio, unsigned int count)
@@ -238,7 +238,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count)
 		bio->bi_flags |= (1 << BIO_REFFED);
 		smp_mb__before_atomic();
 	}
-	atomic_set(&bio->__bi_cnt, count);
+	refcount_set(&bio->__bi_cnt, count);
 }
 
 static inline bool bio_flagged(struct bio *bio, unsigned int bit)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 61339bc..f6e5daa 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -7,6 +7,7 @@
 
 #include <linux/types.h>
 #include <linux/bvec.h>
+#include <linux/refcount.h>
 
 struct bio_set;
 struct bio;
@@ -81,7 +82,7 @@ struct bio {
 
 	unsigned short		bi_max_vecs;	/* max bvl_vecs we can hold */
 
-	atomic_t		__bi_cnt;	/* pin count */
+	refcount_t		__bi_cnt;	/* pin count */
 
 	struct bio_vec		*bi_io_vec;	/* the actual vec list */
 
-- 
2.7.4

[PATCH 2/5] block: convert blk_queue_tag.refcnt from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 block/blk-tag.c        | 8 ++++----
 include/linux/blkdev.h | 3 ++-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/block/blk-tag.c b/block/blk-tag.c
index 07cc329..d83555e 100644
--- a/block/blk-tag.c
+++ b/block/blk-tag.c
@@ -35,7 +35,7 @@ EXPORT_SYMBOL(blk_queue_find_tag);
  */
 void blk_free_tags(struct blk_queue_tag *bqt)
 {
-	if (atomic_dec_and_test(&bqt->refcnt)) {
+	if (refcount_dec_and_test(&bqt->refcnt)) {
 		BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
 							bqt->max_depth);
 
@@ -130,7 +130,7 @@ static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
 	if (init_tag_map(q, tags, depth))
 		goto fail;
 
-	atomic_set(&tags->refcnt, 1);
+	refcount_set(&tags->refcnt, 1);
 	tags->alloc_policy = alloc_policy;
 	tags->next_tag = 0;
 	return tags;
@@ -180,7 +180,7 @@ int blk_queue_init_tags(struct request_queue *q, int depth,
 		queue_flag_set(QUEUE_FLAG_QUEUED, q);
 		return 0;
 	} else
-		atomic_inc(&tags->refcnt);
+		refcount_inc(&tags->refcnt);
 
 	/*
 	 * assign it, all done
@@ -225,7 +225,7 @@ int blk_queue_resize_tags(struct request_queue *q, int new_depth)
 	 * Currently cannot replace a shared tag map with a new
 	 * one, so error out if this is the case
 	 */
-	if (atomic_read(&bqt->refcnt) != 1)
+	if (refcount_read(&bqt->refcnt) != 1)
 		return -EBUSY;
 
 	/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ddd36b..3efc8cf 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -26,6 +26,7 @@
 #include <linux/percpu-refcount.h>
 #include <linux/scatterlist.h>
 #include <linux/blkzoned.h>
+#include <linux/refcount.h>
 
 struct module;
 struct scsi_ioctl_command;
@@ -293,7 +294,7 @@ struct blk_queue_tag {
 	unsigned long *tag_map;		/* bit map of free/busy tags */
 	int max_depth;			/* what we will send to device */
 	int real_max_depth;		/* what the array can hold */
-	atomic_t refcnt;		/* map can be shared */
+	refcount_t refcnt;		/* map can be shared */
 	int alloc_policy;		/* tag allocation policy */
 	int next_tag;			/* next tag */
 };
-- 
2.7.4

[PATCH 3/5] block: convert blkcg_gq.refcnt from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 block/blk-cgroup.c         | 2 +-
 include/linux/blk-cgroup.h | 9 ++++-----
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 0480892..3762908 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -107,7 +107,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
 	blkg->q = q;
 	INIT_LIST_HEAD(&blkg->q_node);
 	blkg->blkcg = blkcg;
-	atomic_set(&blkg->refcnt, 1);
+	refcount_set(&blkg->refcnt, 1);
 
 	/* root blkg uses @q->root_rl, init rl only for !root blkgs */
 	if (blkcg != &blkcg_root) {
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 01b62e7..e54f048 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -19,6 +19,7 @@
 #include <linux/radix-tree.h>
 #include <linux/blkdev.h>
 #include <linux/atomic.h>
+#include <linux/refcount.h>
 
 /* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
 #define BLKG_STAT_CPU_BATCH	(INT_MAX / 2)
@@ -122,7 +123,7 @@ struct blkcg_gq {
 	struct request_list		rl;
 
 	/* reference count */
-	atomic_t			refcnt;
+	refcount_t			refcnt;
 
 	/* is this blkg online? protected by both blkcg and q locks */
 	bool				online;
@@ -354,8 +355,7 @@ static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
  */
 static inline void blkg_get(struct blkcg_gq *blkg)
 {
-	WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
-	atomic_inc(&blkg->refcnt);
+	refcount_inc(&blkg->refcnt);
 }
 
 void __blkg_release_rcu(struct rcu_head *rcu);
@@ -366,8 +366,7 @@ void __blkg_release_rcu(struct rcu_head *rcu);
  */
 static inline void blkg_put(struct blkcg_gq *blkg)
 {
-	WARN_ON_ONCE(atomic_read(&blkg->refcnt) <= 0);
-	if (atomic_dec_and_test(&blkg->refcnt))
+	if (refcount_dec_and_test(&blkg->refcnt))
 		call_rcu(&blkg->rcu_head, __blkg_release_rcu);
 }
 
-- 
2.7.4

[PATCH 4/5] block: convert io_context.active_ref from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 block/bfq-iosched.c       | 2 +-
 block/blk-ioc.c           | 4 ++--
 block/cfq-iosched.c       | 4 ++--
 include/linux/iocontext.h | 6 +++---
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index ed93da2..3a525ab 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -3988,7 +3988,7 @@ static void bfq_update_idle_window(struct bfq_data *bfqd,
 
 	enable_idle = bfq_bfqq_idle_window(bfqq);
 
-	if (atomic_read(&bic->icq.ioc->active_ref) == 0 ||
+	if (refcount_read(&bic->icq.ioc->active_ref) == 0 ||
 	    bfqd->bfq_slice_idle == 0 ||
 		(bfqd->hw_tag && BFQQ_SEEKY(bfqq) &&
 			bfqq->wr_coeff == 1))
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 63898d2..69704d2 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -176,7 +176,7 @@ void put_io_context_active(struct io_context *ioc)
 	unsigned long flags;
 	struct io_cq *icq;
 
-	if (!atomic_dec_and_test(&ioc->active_ref)) {
+	if (!refcount_dec_and_test(&ioc->active_ref)) {
 		put_io_context(ioc);
 		return;
 	}
@@ -275,7 +275,7 @@ int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)
 	/* initialize */
 	atomic_long_set(&ioc->refcount, 1);
 	atomic_set(&ioc->nr_tasks, 1);
-	atomic_set(&ioc->active_ref, 1);
+	refcount_set(&ioc->active_ref, 1);
 	spin_lock_init(&ioc->lock);
 	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
 	INIT_HLIST_HEAD(&ioc->icq_list);
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index b7e9c7f..07c416a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2973,7 +2973,7 @@ static void cfq_arm_slice_timer(struct cfq_data *cfqd)
 	 * task has exited, don't wait
 	 */
 	cic = cfqd->active_cic;
-	if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
+	if (!cic || !refcount_read(&cic->icq.ioc->active_ref))
 		return;
 
 	/*
@@ -3965,7 +3965,7 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 
 	if (cfqq->next_rq && req_noidle(cfqq->next_rq))
 		enable_idle = 0;
-	else if (!atomic_read(&cic->icq.ioc->active_ref) ||
+	else if (!refcount_read(&cic->icq.ioc->active_ref) ||
 		 !cfqd->cfq_slice_idle ||
 		 (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
 		enable_idle = 0;
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index df38db2..e47b907 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -3,6 +3,7 @@
 
 #include <linux/radix-tree.h>
 #include <linux/rcupdate.h>
+#include <linux/refcount.h>
 #include <linux/workqueue.h>
 
 enum {
@@ -96,7 +97,7 @@ struct io_cq {
  */
 struct io_context {
 	atomic_long_t refcount;
-	atomic_t active_ref;
+	refcount_t active_ref;
 	atomic_t nr_tasks;
 
 	/* all the fields below are protected by this lock */
@@ -128,9 +129,8 @@ struct io_context {
 static inline void get_io_context_active(struct io_context *ioc)
 {
 	WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
-	WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
 	atomic_long_inc(&ioc->refcount);
-	atomic_inc(&ioc->active_ref);
+	refcount_inc(&ioc->active_ref);
 }
 
 static inline void ioc_task_link(struct io_context *ioc)
-- 
2.7.4

[PATCH 5/5] block: convert bsg_device.ref_count from atomic_t to refcount_t

[Elena Reshetova]

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.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
 block/bsg.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/bsg.c b/block/bsg.c
index 6fd0854..f35e721 100644
--- a/block/bsg.c
+++ b/block/bsg.c
@@ -21,6 +21,7 @@
 #include <linux/idr.h>
 #include <linux/bsg.h>
 #include <linux/slab.h>
+#include <linux/refcount.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_ioctl.h>
@@ -38,7 +39,7 @@ struct bsg_device {
 	struct list_head busy_list;
 	struct list_head done_list;
 	struct hlist_node dev_list;
-	atomic_t ref_count;
+	refcount_t ref_count;
 	int queued_cmds;
 	int done_cmds;
 	wait_queue_head_t wq_done;
@@ -711,7 +712,7 @@ static int bsg_put_device(struct bsg_device *bd)
 
 	mutex_lock(&bsg_mutex);
 
-	do_free = atomic_dec_and_test(&bd->ref_count);
+	do_free = refcount_dec_and_test(&bd->ref_count);
 	if (!do_free) {
 		mutex_unlock(&bsg_mutex);
 		goto out;
@@ -763,7 +764,7 @@ static struct bsg_device *bsg_add_device(struct inode *inode,
 
 	bsg_set_block(bd, file);
 
-	atomic_set(&bd->ref_count, 1);
+	refcount_set(&bd->ref_count, 1);
 	mutex_lock(&bsg_mutex);
 	hlist_add_head(&bd->dev_list, bsg_dev_idx_hash(iminor(inode)));
 
@@ -783,7 +784,7 @@ static struct bsg_device *__bsg_get_device(int minor, struct request_queue *q)
 
 	hlist_for_each_entry(bd, bsg_dev_idx_hash(minor), dev_list) {
 		if (bd->queue == q) {
-			atomic_inc(&bd->ref_count);
+			refcount_inc(&bd->ref_count);
 			goto found;
 		}
 	}
-- 
2.7.4

Re: [PATCH 0/5] v3 block subsystem refcounter conversions

[Jens Axboe]

On 06/27/2017 05:39 AM, Elena Reshetova wrote:
> Changes in v3:
> No changes in patches apart from trivial rebases, but now by
> default refcount_t = atomic_t and uses all atomic standard operations
> unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
> systems that are critical on performance and cannot accept even
> slight delay on the refcounter operations.

Is that true in 4.12-rc, or is that true in a later release once
Linus has pulled those changes in? If the latter, please resend
this when those changes are in, thanks.

-- 
Jens Axboe

Re: [PATCH 0/5] v3 block subsystem refcounter conversions

[Kees Cook]

On Tue, Jun 27, 2017 at 6:26 AM, Jens Axboe <axboe@kernel.dk> wrote:
> On 06/27/2017 05:39 AM, Elena Reshetova wrote:
>> Changes in v3:
>> No changes in patches apart from trivial rebases, but now by
>> default refcount_t = atomic_t and uses all atomic standard operations
>> unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
>> systems that are critical on performance and cannot accept even
>> slight delay on the refcounter operations.
>
> Is that true in 4.12-rc, or is that true in a later release once
> Linus has pulled those changes in? If the latter, please resend
> this when those changes are in, thanks.

It's in -next currently ("locking/refcount: Create unchecked atomic_t
implementation")

-Kees

-- 
Kees Cook
Pixel Security

RE: [PATCH 0/5] v3 block subsystem refcounter conversions

[Reshetova, Elena]

> Subject: Re: [PATCH 0/5] v3 block subsystem refcounter conversions
> 
> On Tue, Jun 27, 2017 at 6:26 AM, Jens Axboe <axboe@kernel.dk> wrote:
> > On 06/27/2017 05:39 AM, Elena Reshetova wrote:
> >> Changes in v3:
> >> No changes in patches apart from trivial rebases, but now by
> >> default refcount_t = atomic_t and uses all atomic standard operations
> >> unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
> >> systems that are critical on performance and cannot accept even
> >> slight delay on the refcounter operations.
> >
> > Is that true in 4.12-rc, or is that true in a later release once
> > Linus has pulled those changes in? If the latter, please resend
> > this when those changes are in, thanks.
> 
> It's in -next currently ("locking/refcount: Create unchecked atomic_t
> implementation")

I would really like to start discussion on the these patches asap since it normally takes
 some adjustments etc. before they can be merged and we want many changes to go into
next release round and not to miss the merge window. 

Best Regards,
Elena.

> 
> -Kees
> 
> --
> Kees Cook
> Pixel Security

Re: [PATCH 0/5] v3 block subsystem refcounter conversions

[Jens Axboe]

On 06/28/2017 05:58 AM, Reshetova, Elena wrote:
> 
>> Subject: Re: [PATCH 0/5] v3 block subsystem refcounter conversions
>>
>> On Tue, Jun 27, 2017 at 6:26 AM, Jens Axboe <axboe@kernel.dk> wrote:
>>> On 06/27/2017 05:39 AM, Elena Reshetova wrote:
>>>> Changes in v3:
>>>> No changes in patches apart from trivial rebases, but now by
>>>> default refcount_t = atomic_t and uses all atomic standard operations
>>>> unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
>>>> systems that are critical on performance and cannot accept even
>>>> slight delay on the refcounter operations.
>>>
>>> Is that true in 4.12-rc, or is that true in a later release once
>>> Linus has pulled those changes in? If the latter, please resend
>>> this when those changes are in, thanks.
>>
>> It's in -next currently ("locking/refcount: Create unchecked atomic_t
>> implementation")
> 
> I would really like to start discussion on the these patches asap
> since it normally takes some adjustments etc. before they can be
> merged and we want many changes to go into next release round and not
> to miss the merge window. 

As far as I'm concerned, there's no need for a discussion on these. If
the other patches go in to make it as light weight as what we currently
have, then I'm fine with it. I can queue it up for post initial merge
submission.

-- 
Jens Axboe

RE: [PATCH 0/5] v3 block subsystem refcounter conversions

[Reshetova, Elena]

> On 06/28/2017 05:58 AM, Reshetova, Elena wrote:
> >
> >> Subject: Re: [PATCH 0/5] v3 block subsystem refcounter conversions
> >>
> >> On Tue, Jun 27, 2017 at 6:26 AM, Jens Axboe <axboe@kernel.dk> wrote:
> >>> On 06/27/2017 05:39 AM, Elena Reshetova wrote:
> >>>> Changes in v3:
> >>>> No changes in patches apart from trivial rebases, but now by
> >>>> default refcount_t = atomic_t and uses all atomic standard operations
> >>>> unless CONFIG_REFCOUNT_FULL is enabled. This is a compromize for the
> >>>> systems that are critical on performance and cannot accept even
> >>>> slight delay on the refcounter operations.
> >>>
> >>> Is that true in 4.12-rc, or is that true in a later release once
> >>> Linus has pulled those changes in? If the latter, please resend
> >>> this when those changes are in, thanks.
> >>
> >> It's in -next currently ("locking/refcount: Create unchecked atomic_t
> >> implementation")
> >
> > I would really like to start discussion on the these patches asap
> > since it normally takes some adjustments etc. before they can be
> > merged and we want many changes to go into next release round and not
> > to miss the merge window.
> 
> As far as I'm concerned, there's no need for a discussion on these. If
> the other patches go in to make it as light weight as what we currently
> have, then I'm fine with it. I can queue it up for post initial merge
> submission.

Ok, fair enough. Thank you very much!

Best Regards,
Elena.

> 
> --
> Jens Axboe