[04/65] mm: Extract might_alloc() debug check

Commit Message

Daniel Vetter Oct. 23, 2020, 12:21 p.m. UTC

Extracted from slab.h, which seems to have the most complete version
including the correct might_sleep() check. Roll it out to slob.c.

Motivated by a discussion with Paul about possibly changing call_rcu
behaviour to allocate memory, but only roughly every 500th call.

There are a lot fewer places in the kernel that care about whether
allocating memory is allowed or not (due to deadlocks with reclaim
code) than places that care whether sleeping is allowed. But debugging
these also tends to be a lot harder, so nice descriptive checks could
come in handy. I might have some use eventually for annotations in
drivers/gpu.

Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
does not consult the PF_MEMALLOC flags. But there is no flag
equivalent for GFP_NOWAIT, hence this check can't go wrong due to
memalloc_no*_save/restore contexts.

Cc: Paul E. McKenney <[e-mail]>
Cc: Christoph Lameter <[e-mail]>
Cc: Pekka Enberg <[e-mail]>
Cc: David Rientjes <[e-mail]>
Cc: Joonsoo Kim <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: Michel Lespinasse <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Waiman Long <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Dave Chinner <[e-mail]>
Cc: Qian Cai <[e-mail]>
Cc: [e-mail]
Signed-off-by: Daniel Vetter <[e-mail]>
---
 include/linux/sched/mm.h | 16 ++++++++++++++++
 mm/slab.h                |  5 +----
 mm/slob.c                |  6 ++----
 3 files changed, 19 insertions(+), 8 deletions(-)

Comments

Vlastimil Babka Oct. 23, 2020, 2:14 p.m. UTC | #1

On 10/23/20 2:21 PM, Daniel Vetter wrote:
> Extracted from slab.h, which seems to have the most complete version
> including the correct might_sleep() check. Roll it out to slob.c.
> 
> Motivated by a discussion with Paul about possibly changing call_rcu
> behaviour to allocate memory, but only roughly every 500th call.
> 
> There are a lot fewer places in the kernel that care about whether
> allocating memory is allowed or not (due to deadlocks with reclaim
> code) than places that care whether sleeping is allowed. But debugging
> these also tends to be a lot harder, so nice descriptive checks could
> come in handy. I might have some use eventually for annotations in
> drivers/gpu.
> 
> Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> does not consult the PF_MEMALLOC flags. But there is no flag
> equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> memalloc_no*_save/restore contexts.
> 
> Cc: Paul E. McKenney <[e-mail]>
> Cc: Christoph Lameter <[e-mail]>
> Cc: Pekka Enberg <[e-mail]>
> Cc: David Rientjes <[e-mail]>
> Cc: Joonsoo Kim <[e-mail]>
> Cc: Andrew Morton <[e-mail]>
> Cc: Peter Zijlstra <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: Vlastimil Babka <[e-mail]>
> Cc: Mathieu Desnoyers <[e-mail]>
> Cc: Sebastian Andrzej Siewior <[e-mail]>
> Cc: Michel Lespinasse <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Cc: Waiman Long <[e-mail]>
> Cc: Thomas Gleixner <[e-mail]>
> Cc: Randy Dunlap <[e-mail]>
> Cc: [e-mail]
> Cc: [e-mail]
> Cc: Dave Chinner <[e-mail]>
> Cc: Qian Cai <[e-mail]>
> Cc: [e-mail]
> Signed-off-by: Daniel Vetter <[e-mail]>

Looks useful.
Acked-by: Vlastimil Babka <[e-mail]>

Matthew Wilcox Oct. 23, 2020, 2:16 p.m. UTC | #2

On Fri, Oct 23, 2020 at 02:21:15PM +0200, Daniel Vetter wrote:
> Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> does not consult the PF_MEMALLOC flags. But there is no flag
> equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> memalloc_no*_save/restore contexts.

I have a patch series that adds memalloc_nowait_save/restore.

https://lore.kernel.org/linux-mm/[e-mail]/

Daniel Vetter Oct. 23, 2020, 2:37 p.m. UTC | #3

On Fri, Oct 23, 2020 at 4:16 PM Matthew Wilcox <[e-mail]> wrote:
>
> On Fri, Oct 23, 2020 at 02:21:15PM +0200, Daniel Vetter wrote:
> > Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> > does not consult the PF_MEMALLOC flags. But there is no flag
> > equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> > memalloc_no*_save/restore contexts.
>
> I have a patch series that adds memalloc_nowait_save/restore.

tbh this was a typoed git send-email, but thanks for the heads-up,
I'll adjust the patch accordingly.

Cheers, Daniel

> https://lore.kernel.org/linux-mm/[e-mail]/

Daniel Vetter Oct. 23, 2020, 2:45 p.m. UTC | #4

On Fri, Oct 23, 2020 at 4:37 PM Daniel Vetter <[e-mail]> wrote:
>
> On Fri, Oct 23, 2020 at 4:16 PM Matthew Wilcox <[e-mail]> wrote:
> >
> > On Fri, Oct 23, 2020 at 02:21:15PM +0200, Daniel Vetter wrote:
> > > Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> > > does not consult the PF_MEMALLOC flags. But there is no flag
> > > equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> > > memalloc_no*_save/restore contexts.
> >
> > I have a patch series that adds memalloc_nowait_save/restore.
>
> tbh this was a typoed git send-email, but thanks for the heads-up,
> I'll adjust the patch accordingly.

On 2nd thought I think your patch should update
gfpflags_allow_blocking to take into account the new ->memalloc_nowait
flag you're adding. I'll comment over there in that thread.
-Daniel

>
> > https://lore.kernel.org/linux-mm/[e-mail]/
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

Paul E. McKenney Oct. 23, 2020, 8:53 p.m. UTC | #5

On Fri, Oct 23, 2020 at 02:21:15PM +0200, Daniel Vetter wrote:
> Extracted from slab.h, which seems to have the most complete version
> including the correct might_sleep() check. Roll it out to slob.c.
> 
> Motivated by a discussion with Paul about possibly changing call_rcu
> behaviour to allocate memory, but only roughly every 500th call.
> 
> There are a lot fewer places in the kernel that care about whether
> allocating memory is allowed or not (due to deadlocks with reclaim
> code) than places that care whether sleeping is allowed. But debugging
> these also tends to be a lot harder, so nice descriptive checks could
> come in handy. I might have some use eventually for annotations in
> drivers/gpu.
> 
> Note that unlike fs_reclaim_acquire/release gfpflags_allow_blocking
> does not consult the PF_MEMALLOC flags. But there is no flag
> equivalent for GFP_NOWAIT, hence this check can't go wrong due to
> memalloc_no*_save/restore contexts.
> 
> Cc: Paul E. McKenney <[e-mail]>
> Cc: Christoph Lameter <[e-mail]>
> Cc: Pekka Enberg <[e-mail]>
> Cc: David Rientjes <[e-mail]>
> Cc: Joonsoo Kim <[e-mail]>
> Cc: Andrew Morton <[e-mail]>
> Cc: Peter Zijlstra <[e-mail]>
> Cc: Ingo Molnar <[e-mail]>
> Cc: Vlastimil Babka <[e-mail]>
> Cc: Mathieu Desnoyers <[e-mail]>
> Cc: Sebastian Andrzej Siewior <[e-mail]>
> Cc: Michel Lespinasse <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Cc: Waiman Long <[e-mail]>
> Cc: Thomas Gleixner <[e-mail]>
> Cc: Randy Dunlap <[e-mail]>
> Cc: [e-mail]
> Cc: [e-mail]
> Cc: Dave Chinner <[e-mail]>
> Cc: Qian Cai <[e-mail]>
> Cc: [e-mail]
> Signed-off-by: Daniel Vetter <[e-mail]>

Nice!!!

Acked-by: Paul E. McKenney <[e-mail]>

> ---
>  include/linux/sched/mm.h | 16 ++++++++++++++++
>  mm/slab.h                |  5 +----
>  mm/slob.c                |  6 ++----
>  3 files changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index f889e332912f..2b0037abac0b 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -205,6 +205,22 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
>  static inline void fs_reclaim_release(gfp_t gfp_mask) { }
>  #endif
>  
> +/**
> + * might_alloc - Marks possible allocation sites
> + * @gfp_mask: gfp_t flags that would be use to allocate
> + *
> + * Similar to might_sleep() and other annotations this can be used in functions
> + * that might allocate, but often dont. Compiles to nothing without
> + * CONFIG_LOCKDEP. Includes a conditional might_sleep() if @gfp allows blocking.
> + */
> +static inline void might_alloc(gfp_t gfp_mask)
> +{
> +	fs_reclaim_acquire(gfp_mask);
> +	fs_reclaim_release(gfp_mask);
> +
> +	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
> +}
> +
>  /**
>   * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
>   *
> diff --git a/mm/slab.h b/mm/slab.h
> index 6cc323f1313a..fedd789b2270 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -492,10 +492,7 @@ static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
>  {
>  	flags &= gfp_allowed_mask;
>  
> -	fs_reclaim_acquire(flags);
> -	fs_reclaim_release(flags);
> -
> -	might_sleep_if(gfpflags_allow_blocking(flags));
> +	might_alloc(flags);
>  
>  	if (should_failslab(s, flags))
>  		return NULL;
> diff --git a/mm/slob.c b/mm/slob.c
> index 7cc9805c8091..8d4bfa46247f 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -474,8 +474,7 @@ __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
>  
>  	gfp &= gfp_allowed_mask;
>  
> -	fs_reclaim_acquire(gfp);
> -	fs_reclaim_release(gfp);
> +	might_alloc(gfp);
>  
>  	if (size < PAGE_SIZE - minalign) {
>  		int align = minalign;
> @@ -597,8 +596,7 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
>  
>  	flags &= gfp_allowed_mask;
>  
> -	fs_reclaim_acquire(flags);
> -	fs_reclaim_release(flags);
> +	might_alloc(flags);
>  
>  	if (c->size < PAGE_SIZE) {
>  		b = slob_alloc(c->size, flags, c->align, node, 0);
> -- 
> 2.28.0
>

Patch

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index f889e332912f..2b0037abac0b 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -205,6 +205,22 @@  static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }
 static inline void fs_reclaim_release(gfp_t gfp_mask) { }
 #endif
 
+/**
+ * might_alloc - Marks possible allocation sites
+ * @gfp_mask: gfp_t flags that would be use to allocate
+ *
+ * Similar to might_sleep() and other annotations this can be used in functions
+ * that might allocate, but often dont. Compiles to nothing without
+ * CONFIG_LOCKDEP. Includes a conditional might_sleep() if @gfp allows blocking.
+ */
+static inline void might_alloc(gfp_t gfp_mask)
+{
+	fs_reclaim_acquire(gfp_mask);
+	fs_reclaim_release(gfp_mask);
+
+	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
+}
+
 /**
  * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
  *
diff --git a/mm/slab.h b/mm/slab.h
index 6cc323f1313a..fedd789b2270 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -492,10 +492,7 @@  static inline struct kmem_cache *slab_pre_alloc_hook(struct kmem_cache *s,
 {
 	flags &= gfp_allowed_mask;
 
-	fs_reclaim_acquire(flags);
-	fs_reclaim_release(flags);
-
-	might_sleep_if(gfpflags_allow_blocking(flags));
+	might_alloc(flags);
 
 	if (should_failslab(s, flags))
 		return NULL;
diff --git a/mm/slob.c b/mm/slob.c
index 7cc9805c8091..8d4bfa46247f 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -474,8 +474,7 @@  __do_kmalloc_node(size_t size, gfp_t gfp, int node, unsigned long caller)
 
 	gfp &= gfp_allowed_mask;
 
-	fs_reclaim_acquire(gfp);
-	fs_reclaim_release(gfp);
+	might_alloc(gfp);
 
 	if (size < PAGE_SIZE - minalign) {
 		int align = minalign;
@@ -597,8 +596,7 @@  static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
 
 	flags &= gfp_allowed_mask;
 
-	fs_reclaim_acquire(flags);
-	fs_reclaim_release(flags);
+	might_alloc(flags);
 
 	if (c->size < PAGE_SIZE) {
 		b = slob_alloc(c->size, flags, c->align, node, 0);