[PATCH 0/6] use irqsafe variant of refcount_dec_and_lock() / atomic_dec_and_lock()

[PATCH 0/6] use irqsafe variant of refcount_dec_and_lock() / atomic_dec_and_lock()

[Sebastian Andrzej Siewior]

The irqsave variant of refcount_dec_and_lock() and atomic_dec_and_lock()
made it into v4.18-rc2. This is just a repost of the users so that they
can be routed through the individual subsystems.
 
Sebastian
 
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org

[PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Sebastian Andrzej Siewior]

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

The irqsave variant of atomic_dec_and_lock handles irqsave/restore when
taking/releasing the spin lock. With this variant the call of
local_irq_save is no longer required.

Cc: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/md/raid5.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 2031506a0ecd..e933bff9459e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -409,16 +409,15 @@ void raid5_release_stripe(struct stripe_head *sh)
 		md_wakeup_thread(conf->mddev->thread);
 	return;
 slow_path:
-	local_irq_save(flags);
 	/* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
-	if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
+	if (atomic_dec_and_lock_irqsave(&sh->count, &conf->device_lock, flags)) {
 		INIT_LIST_HEAD(&list);
 		hash = sh->hash_lock_index;
 		do_release_stripe(conf, sh, &list);
 		spin_unlock(&conf->device_lock);
 		release_inactive_stripe_list(conf, &list, hash);
+		local_irq_restore(flags);
 	}
-	local_irq_restore(flags);
 }
 
 static inline void remove_hash(struct stripe_head *sh)
-- 
2.18.0

Re: [PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Sebastian Andrzej Siewior]

On 2018-07-03 22:01:36 [+0200], To linux-kernel@vger.kernel.org wrote:
> From: Anna-Maria Gleixner <anna-maria@linutronix.de>
> 
> The irqsave variant of atomic_dec_and_lock handles irqsave/restore when
> taking/releasing the spin lock. With this variant the call of
> local_irq_save is no longer required.

Shaohua, are you with this?

> Cc: Shaohua Li <shli@kernel.org>
> Cc: linux-raid@vger.kernel.org
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/md/raid5.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 2031506a0ecd..e933bff9459e 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -409,16 +409,15 @@ void raid5_release_stripe(struct stripe_head *sh)
>  		md_wakeup_thread(conf->mddev->thread);
>  	return;
>  slow_path:
> -	local_irq_save(flags);
>  	/* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
> -	if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
> +	if (atomic_dec_and_lock_irqsave(&sh->count, &conf->device_lock, flags)) {
>  		INIT_LIST_HEAD(&list);
>  		hash = sh->hash_lock_index;
>  		do_release_stripe(conf, sh, &list);
>  		spin_unlock(&conf->device_lock);
>  		release_inactive_stripe_list(conf, &list, hash);
> +		local_irq_restore(flags);
>  	}
> -	local_irq_restore(flags);
>  }
>  
>  static inline void remove_hash(struct stripe_head *sh)
> -- 
> 2.18.0
> 

Re: [PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Shaohua Li]

On Mon, Jul 16, 2018 at 02:27:40PM +0200, Sebastian Andrzej Siewior wrote:
> On 2018-07-03 22:01:36 [+0200], To linux-kernel@vger.kernel.org wrote:
> > From: Anna-Maria Gleixner <anna-maria@linutronix.de>
> > 
> > The irqsave variant of atomic_dec_and_lock handles irqsave/restore when
> > taking/releasing the spin lock. With this variant the call of
> > local_irq_save is no longer required.
> 
> Shaohua, are you with this?

Acked-by: Shaohua Li <shli@kernel.org> 
> > Cc: Shaohua Li <shli@kernel.org>
> > Cc: linux-raid@vger.kernel.org
> > Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  drivers/md/raid5.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index 2031506a0ecd..e933bff9459e 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -409,16 +409,15 @@ void raid5_release_stripe(struct stripe_head *sh)
> >  		md_wakeup_thread(conf->mddev->thread);
> >  	return;
> >  slow_path:
> > -	local_irq_save(flags);
> >  	/* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
> > -	if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
> > +	if (atomic_dec_and_lock_irqsave(&sh->count, &conf->device_lock, flags)) {
> >  		INIT_LIST_HEAD(&list);
> >  		hash = sh->hash_lock_index;
> >  		do_release_stripe(conf, sh, &list);
> >  		spin_unlock(&conf->device_lock);
> >  		release_inactive_stripe_list(conf, &list, hash);
> > +		local_irq_restore(flags);
> >  	}
> > -	local_irq_restore(flags);
> >  }
> >  
> >  static inline void remove_hash(struct stripe_head *sh)
> > -- 
> > 2.18.0
> > 

Re: [PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Sebastian Andrzej Siewior]

On 2018-07-16 17:37:27 [-0700], Shaohua Li wrote:
> On Mon, Jul 16, 2018 at 02:27:40PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2018-07-03 22:01:36 [+0200], To linux-kernel@vger.kernel.org wrote:
> > > From: Anna-Maria Gleixner <anna-maria@linutronix.de>
> > > 
> > > The irqsave variant of atomic_dec_and_lock handles irqsave/restore when
> > > taking/releasing the spin lock. With this variant the call of
> > > local_irq_save is no longer required.
> > 
> > Shaohua, are you with this?
> 
> Acked-by: Shaohua Li <shli@kernel.org> 

Thank you. 
Is there a reason why you did not apply it or are you too busy now and
do it later (and just signal the ack that you are fine with it)?

Sebastian

Re: [PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Shaohua Li]

On Wed, Jul 18, 2018 at 12:57:21PM +0200, Sebastian Andrzej Siewior wrote:
> On 2018-07-16 17:37:27 [-0700], Shaohua Li wrote:
> > On Mon, Jul 16, 2018 at 02:27:40PM +0200, Sebastian Andrzej Siewior wrote:
> > > On 2018-07-03 22:01:36 [+0200], To linux-kernel@vger.kernel.org wrote:
> > > > From: Anna-Maria Gleixner <anna-maria@linutronix.de>
> > > > 
> > > > The irqsave variant of atomic_dec_and_lock handles irqsave/restore when
> > > > taking/releasing the spin lock. With this variant the call of
> > > > local_irq_save is no longer required.
> > > 
> > > Shaohua, are you with this?
> > 
> > Acked-by: Shaohua Li <shli@kernel.org> 
> 
> Thank you. 
> Is there a reason why you did not apply it or are you too busy now and
> do it later (and just signal the ack that you are fine with it)?

Since you sent a series, I suppose you want someone else to take it. But I can
take it for sure, will do soon.

Thanks,
Shaohua

Re: [PATCH 1/6] drivers/md/raid5: Use irqsave variant of atomic_dec_and_lock()

[Sebastian Andrzej Siewior]

On 2018-07-18 19:44:05 [-0700], Shaohua Li wrote:
> Since you sent a series, I suppose you want someone else to take it. But I can
> take it for sure, will do soon.

I'm sorry for the miss understanding. I tried to explain this in the
cover letter. The prerequisites are already merged so then the actual
changes can be merged via the individual maintainer.
Thank you Shaohua.

> Thanks,
> Shaohua

Sebastian

[PATCH 2/6] drivers/md/raid5: Do not disable irq on release_inactive_stripe_list() call

[Sebastian Andrzej Siewior]

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

There is no need to invoke release_inactive_stripe_list() with interrupts
disabled. All call sites, except raid5_release_stripe(), unlock
->device_lock and enable interrupts before invoking the function.

Make it consistent.

Cc: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/md/raid5.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index e933bff9459e..ca1dd0cb04c5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -414,9 +414,8 @@ void raid5_release_stripe(struct stripe_head *sh)
 		INIT_LIST_HEAD(&list);
 		hash = sh->hash_lock_index;
 		do_release_stripe(conf, sh, &list);
-		spin_unlock(&conf->device_lock);
+		spin_unlock_irqrestore(&conf->device_lock, flags);
 		release_inactive_stripe_list(conf, &list, hash);
-		local_irq_restore(flags);
 	}
 }
 
-- 
2.18.0

Re: [PATCH 2/6] drivers/md/raid5: Do not disable irq on release_inactive_stripe_list() call

[Sebastian Andrzej Siewior]

On 2018-07-03 22:01:37 [+0200], To linux-kernel@vger.kernel.org wrote:
> From: Anna-Maria Gleixner <anna-maria@linutronix.de>
> 
> There is no need to invoke release_inactive_stripe_list() with interrupts
> disabled. All call sites, except raid5_release_stripe(), unlock
> ->device_lock and enable interrupts before invoking the function.
> 
> Make it consistent.

Shaohua, I've seen that you already applied 1/6. Could you also please
apply this one? This is the only remaining raid5 patch :)

> Cc: Shaohua Li <shli@kernel.org>
> Cc: linux-raid@vger.kernel.org
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/md/raid5.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index e933bff9459e..ca1dd0cb04c5 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -414,9 +414,8 @@ void raid5_release_stripe(struct stripe_head *sh)
>  		INIT_LIST_HEAD(&list);
>  		hash = sh->hash_lock_index;
>  		do_release_stripe(conf, sh, &list);
> -		spin_unlock(&conf->device_lock);
> +		spin_unlock_irqrestore(&conf->device_lock, flags);
>  		release_inactive_stripe_list(conf, &list, hash);
> -		local_irq_restore(flags);
>  	}
>  }
>  

Sebastian

[PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t

[Sebastian Andrzej Siewior]

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.

Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 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 24251762c20c..9a6bc0951cfa 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;
@@ -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
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 2e5d3df0853d..55a233d75f39 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -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) {
-- 
2.18.0

Re: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t

[Sebastian Andrzej Siewior]

On 2018-07-03 22:01:38 [+0200], To linux-kernel@vger.kernel.org wrote:
> 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.

Andrew, is it okay for you to collect this one (and 4/6 of this series,
both bdi)? The prerequisites are already in Linus' tree.

> Cc: linux-mm@kvack.org
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  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 24251762c20c..9a6bc0951cfa 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;
> @@ -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
> 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 2e5d3df0853d..55a233d75f39 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -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) {
> -- 
> 2.18.0

Sebastian

Re: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t

[Andrew Morton]

On Tue,  3 Jul 2018 22:01:38 +0200 Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> 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.
> 
> ...
>
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -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;
>
> ...
>

I'm not sure that the restructuring of wb_congested_get_create() was
desirable and it does make the patch harder to review.  But it looks
OK to me.

Re: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t

[Sebastian Andrzej Siewior]

On 2018-07-16 15:57:16 [-0700], Andrew Morton wrote:
> > --- a/mm/backing-dev.c
> > +++ b/mm/backing-dev.c
> > @@ -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;
> >
> > ...
> >
> 
> I'm not sure that the restructuring of wb_congested_get_create() was
> desirable and it does make the patch harder to review.  But it looks
> OK to me.

By `restructuring' you mean the addition of return statement instead
using the goto label in the first hunk? If so, then you would have

	refcount_set(&new_congested->refcnt, 0);
	refcount_inc(&congested->refcnt);

which is a 0 -> 1 transition and is forbidden by refcount_t. So I had to
avoid this one.

Thank you applying the patches!

You applied the bdi and userns switch from atomic_t to refcount_t.
There were also the patches
  [PATCH 4/6] bdi: Use irqsave variant of refcount_dec_and_lock()
  [PATCH 6/6] userns: Use irqsave variant of refcount_dec_and_lock()

in the series which make use the irqsave version of
refcount_dec_and_lock(). Did you miss them by chance or skipped them on
purpose?

Sebastian

[PATCH 4/6] bdi: Use irqsave variant of refcount_dec_and_lock()

[Sebastian Andrzej Siewior]

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

The irqsave variant of refcount_dec_and_lock handles irqsave/restore when
taking/releasing the spin lock. With this variant the call of
local_irq_save/restore is no longer required.

Cc: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
[bigeasy: s@atomic_dec_and_lock@refcount_dec_and_lock@g ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/backing-dev.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 55a233d75f39..f5981e9d6ae2 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -473,11 +473,8 @@ void wb_congested_put(struct bdi_writeback_congested *congested)
 {
 	unsigned long flags;
 
-	local_irq_save(flags);
-	if (!refcount_dec_and_lock(&congested->refcnt, &cgwb_lock)) {
-		local_irq_restore(flags);
+	if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags))
 		return;
-	}
 
 	/* bdi might already have been destroyed leaving @congested unlinked */
 	if (congested->__bdi) {
-- 
2.18.0

[PATCH 5/6] userns: Use refcount_t for reference counting instead atomic_t

[Sebastian Andrzej Siewior]

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.

Cc: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/sched/user.h | 5 +++--
 kernel/user.c              | 8 ++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 96fe289c4c6e..39ad98c09c58 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -4,6 +4,7 @@
 
 #include <linux/uidgid.h>
 #include <linux/atomic.h>
+#include <linux/refcount.h>
 #include <linux/ratelimit.h>
 
 struct key;
@@ -12,7 +13,7 @@ struct key;
  * Some day this will be a full-fledged user tracking system..
  */
 struct user_struct {
-	atomic_t __count;	/* reference count */
+	refcount_t __count;	/* reference count */
 	atomic_t processes;	/* How many processes does this user have? */
 	atomic_t sigpending;	/* How many pending signals does this user have? */
 #ifdef CONFIG_FANOTIFY
@@ -59,7 +60,7 @@ extern struct user_struct root_user;
 extern struct user_struct * alloc_uid(kuid_t);
 static inline struct user_struct *get_uid(struct user_struct *u)
 {
-	atomic_inc(&u->__count);
+	refcount_inc(&u->__count);
 	return u;
 }
 extern void free_uid(struct user_struct *);
diff --git a/kernel/user.c b/kernel/user.c
index 36288d840675..5f65ef195259 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -96,7 +96,7 @@ static DEFINE_SPINLOCK(uidhash_lock);
 
 /* root_user.__count is 1, for init task cred */
 struct user_struct root_user = {
-	.__count	= ATOMIC_INIT(1),
+	.__count	= REFCOUNT_INIT(1),
 	.processes	= ATOMIC_INIT(1),
 	.sigpending	= ATOMIC_INIT(0),
 	.locked_shm     = 0,
@@ -123,7 +123,7 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 
 	hlist_for_each_entry(user, hashent, uidhash_node) {
 		if (uid_eq(user->uid, uid)) {
-			atomic_inc(&user->__count);
+			refcount_inc(&user->__count);
 			return user;
 		}
 	}
@@ -170,7 +170,7 @@ void free_uid(struct user_struct *up)
 		return;
 
 	local_irq_save(flags);
-	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
+	if (refcount_dec_and_lock(&up->__count, &uidhash_lock))
 		free_user(up, flags);
 	else
 		local_irq_restore(flags);
@@ -191,7 +191,7 @@ struct user_struct *alloc_uid(kuid_t uid)
 			goto out_unlock;
 
 		new->uid = uid;
-		atomic_set(&new->__count, 1);
+		refcount_set(&new->__count, 1);
 		ratelimit_state_init(&new->ratelimit, HZ, 100);
 		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
 
-- 
2.18.0

Re: [PATCH 5/6] userns: Use refcount_t for reference counting instead atomic_t

[Sebastian Andrzej Siewior]

On 2018-07-03 22:01:40 [+0200], To linux-kernel@vger.kernel.org wrote:
> 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.

Ingo, Andrew: who of you two feels most comfortable to apply this one
(and 6/6 of this series, both `userns')? If none, who would you suggest?

> Cc: Andrew Morton <akpm@linux-foundation.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  include/linux/sched/user.h | 5 +++--
>  kernel/user.c              | 8 ++++----
>  2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
> index 96fe289c4c6e..39ad98c09c58 100644
> --- a/include/linux/sched/user.h
> +++ b/include/linux/sched/user.h
> @@ -4,6 +4,7 @@
>  
>  #include <linux/uidgid.h>
>  #include <linux/atomic.h>
> +#include <linux/refcount.h>
>  #include <linux/ratelimit.h>
>  
>  struct key;
> @@ -12,7 +13,7 @@ struct key;
>   * Some day this will be a full-fledged user tracking system..
>   */
>  struct user_struct {
> -	atomic_t __count;	/* reference count */
> +	refcount_t __count;	/* reference count */
>  	atomic_t processes;	/* How many processes does this user have? */
>  	atomic_t sigpending;	/* How many pending signals does this user have? */
>  #ifdef CONFIG_FANOTIFY
> @@ -59,7 +60,7 @@ extern struct user_struct root_user;
>  extern struct user_struct * alloc_uid(kuid_t);
>  static inline struct user_struct *get_uid(struct user_struct *u)
>  {
> -	atomic_inc(&u->__count);
> +	refcount_inc(&u->__count);
>  	return u;
>  }
>  extern void free_uid(struct user_struct *);
> diff --git a/kernel/user.c b/kernel/user.c
> index 36288d840675..5f65ef195259 100644
> --- a/kernel/user.c
> +++ b/kernel/user.c
> @@ -96,7 +96,7 @@ static DEFINE_SPINLOCK(uidhash_lock);
>  
>  /* root_user.__count is 1, for init task cred */
>  struct user_struct root_user = {
> -	.__count	= ATOMIC_INIT(1),
> +	.__count	= REFCOUNT_INIT(1),
>  	.processes	= ATOMIC_INIT(1),
>  	.sigpending	= ATOMIC_INIT(0),
>  	.locked_shm     = 0,
> @@ -123,7 +123,7 @@ static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
>  
>  	hlist_for_each_entry(user, hashent, uidhash_node) {
>  		if (uid_eq(user->uid, uid)) {
> -			atomic_inc(&user->__count);
> +			refcount_inc(&user->__count);
>  			return user;
>  		}
>  	}
> @@ -170,7 +170,7 @@ void free_uid(struct user_struct *up)
>  		return;
>  
>  	local_irq_save(flags);
> -	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
> +	if (refcount_dec_and_lock(&up->__count, &uidhash_lock))
>  		free_user(up, flags);
>  	else
>  		local_irq_restore(flags);
> @@ -191,7 +191,7 @@ struct user_struct *alloc_uid(kuid_t uid)
>  			goto out_unlock;
>  
>  		new->uid = uid;
> -		atomic_set(&new->__count, 1);
> +		refcount_set(&new->__count, 1);
>  		ratelimit_state_init(&new->ratelimit, HZ, 100);
>  		ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
>  
> -- 
> 2.18.0

Sebastian

[PATCH 6/6] userns: Use irqsave variant of refcount_dec_and_lock()

[Sebastian Andrzej Siewior]

From: Anna-Maria Gleixner <anna-maria@linutronix.de>

The irqsave variant of refcount_dec_and_lock handles irqsave/restore when
taking/releasing the spin lock. With this variant the call of
local_irq_save/restore is no longer required.

Cc: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
[bigeasy: s@atomic_dec_and_lock@refcount_dec_and_lock@g ]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/user.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/user.c b/kernel/user.c
index 5f65ef195259..0df9b1640b2a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -169,11 +169,8 @@ void free_uid(struct user_struct *up)
 	if (!up)
 		return;
 
-	local_irq_save(flags);
-	if (refcount_dec_and_lock(&up->__count, &uidhash_lock))
+	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
 		free_user(up, flags);
-	else
-		local_irq_restore(flags);
 }
 
 struct user_struct *alloc_uid(kuid_t uid)
-- 
2.18.0