[PATCH 03/65] mm: Track mmu notifiers in fs_reclaim_acquire/release

[PATCH 03/65] mm: Track mmu notifiers in fs_reclaim_acquire/release

[Daniel Vetter]

fs_reclaim_acquire/release nicely catch recursion issues when
allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend
to use to keep the excessive caches in check). For mmu notifier
recursions we do have lockdep annotations since 23b68395c7c7
("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end").

But these only fire if a path actually results in some pte
invalidation - for most small allocations that's very rarely the case.
The other trouble is that pte invalidation can happen any time when
__GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe
choice, GFP_NOIO isn't good enough to avoid potential mmu notifier
recursion.

I was pondering whether we should just do the general annotation, but
there's always the risk for false positives. Plus I'm assuming that
the core fs and io code is a lot better reviewed and tested than
random mmu notifier code in drivers. Hence why I decide to only
annotate for that specific case.

Furthermore even if we'd create a lockdep map for direct reclaim, we'd
still need to explicit pull in the mmu notifier map - there's a lot
more places that do pte invalidation than just direct reclaim, these
two contexts arent the same.

Note that the mmu notifiers needing their own independent lockdep map
is also the reason we can't hold them from fs_reclaim_acquire to
fs_reclaim_release - it would nest with the acquistion in the pte
invalidation code, causing a lockdep splat. And we can't remove the
annotations from pte invalidation and all the other places since
they're called from many other places than page reclaim. Hence we can
only do the equivalent of might_lock, but on the raw lockdep map.

With this we can also remove the lockdep priming added in 66204f1d2d1b
("mm/mmu_notifiers: prime lockdep") since the new annotations are
strictly more powerful.

v2: Review from Thomas Hellstrom:
- unbotch the fs_reclaim context check, I accidentally inverted it,
  but it didn't blow up because I inverted it immediately
- fix compiling for !CONFIG_MMU_NOTIFIER

v3: Unbreak the PF_MEMALLOC_ context flags. Thanks to Qian for the
report and Dave for explaining what I failed to see.

Cc: linux-fsdevel@vger.kernel.org
Cc: Dave Chinner <david@fromorbit.com>
Cc: Qian Cai <cai@lca.pw>
Cc: linux-xfs@vger.kernel.org
Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: linux-mm@kvack.org
Cc: linux-rdma@vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 mm/mmu_notifier.c |  7 -------
 mm/page_alloc.c   | 31 ++++++++++++++++++++-----------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 4fc918163dd3..6bf798373eb0 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription,
 	mmap_assert_write_locked(mm);
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
 
-	if (IS_ENABLED(CONFIG_LOCKDEP)) {
-		fs_reclaim_acquire(GFP_KERNEL);
-		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
-		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
-		fs_reclaim_release(GFP_KERNEL);
-	}
-
 	if (!mm->notifier_subscriptions) {
 		/*
 		 * kmalloc cannot be called under mm_take_all_locks(), but we
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 780c8f023b28..2edd3fd447fa 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -57,6 +57,7 @@
 #include <trace/events/oom.h>
 #include <linux/prefetch.h>
 #include <linux/mm_inline.h>
+#include <linux/mmu_notifier.h>
 #include <linux/migrate.h>
 #include <linux/hugetlb.h>
 #include <linux/sched/rt.h>
@@ -4207,10 +4208,8 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla
 static struct lockdep_map __fs_reclaim_map =
 	STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map);
 
-static bool __need_fs_reclaim(gfp_t gfp_mask)
+static bool __need_reclaim(gfp_t gfp_mask)
 {
-	gfp_mask = current_gfp_context(gfp_mask);
-
 	/* no reclaim without waiting on it */
 	if (!(gfp_mask & __GFP_DIRECT_RECLAIM))
 		return false;
@@ -4219,10 +4218,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask)
 	if (current->flags & PF_MEMALLOC)
 		return false;
 
-	/* We're only interested __GFP_FS allocations for now */
-	if (!(gfp_mask & __GFP_FS))
-		return false;
-
 	if (gfp_mask & __GFP_NOLOCKDEP)
 		return false;
 
@@ -4241,15 +4236,29 @@ void __fs_reclaim_release(void)
 
 void fs_reclaim_acquire(gfp_t gfp_mask)
 {
-	if (__need_fs_reclaim(gfp_mask))
-		__fs_reclaim_acquire();
+	gfp_mask = current_gfp_context(gfp_mask);
+
+	if (__need_reclaim(gfp_mask)) {
+		if (gfp_mask & __GFP_FS)
+			__fs_reclaim_acquire();
+
+#ifdef CONFIG_MMU_NOTIFIER
+		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
+		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
+#endif
+
+	}
 }
 EXPORT_SYMBOL_GPL(fs_reclaim_acquire);
 
 void fs_reclaim_release(gfp_t gfp_mask)
 {
-	if (__need_fs_reclaim(gfp_mask))
-		__fs_reclaim_release();
+	gfp_mask = current_gfp_context(gfp_mask);
+
+	if (__need_reclaim(gfp_mask)) {
+		if (gfp_mask & __GFP_FS)
+			__fs_reclaim_release();
+	}
 }
 EXPORT_SYMBOL_GPL(fs_reclaim_release);
 #endif
-- 
2.28.0

Re: [PATCH 03/65] mm: Track mmu notifiers in fs_reclaim_acquire/release

[Christoph Hellwig]

Is there a list that has the cover letter and the whole series?
I've only found fragments (and mostly the same fragments) while
wading through my backlog in various list folders..

Re: [PATCH 03/65] mm: Track mmu notifiers in fs_reclaim_acquire/release

[Daniel Vetter]

On Tue, Oct 27, 2020 at 7:51 PM Christoph Hellwig <hch@infradead.org> wrote:
> Is there a list that has the cover letter and the whole series?
> I've only found fragments (and mostly the same fragments) while
> wading through my backlog in various list folders..

Typoed git send-email command that I only caught half-way through. I
tried to reply with apologies in a few spots, I guess I didn't cover
all the lists this spams :-/

The patch itself is still somewhere on my todo to respin, I want to
pep it up with some testcases since previous version was kinda badly
broken. Just didn't get around to that yet.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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

[Daniel Vetter]

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 <paulmck@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Waiman Long <longman@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-mm@kvack.org
Cc: linux-fsdevel@vger.kernel.org
Cc: Dave Chinner <david@fromorbit.com>
Cc: Qian Cai <cai@lca.pw>
Cc: linux-xfs@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 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

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

[Vlastimil Babka]

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 <paulmck@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: linux-mm@kvack.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: linux-xfs@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Looks useful.
Acked-by: Vlastimil Babka <vbabka@suse.cz>

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

[Matthew Wilcox]

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/20200625113122.7540-7-willy@infradead.org/

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

[Daniel Vetter]

On Fri, Oct 23, 2020 at 4:16 PM Matthew Wilcox <willy@infradead.org> 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/20200625113122.7540-7-willy@infradead.org/



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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

[Daniel Vetter]

On Fri, Oct 23, 2020 at 4:37 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> On Fri, Oct 23, 2020 at 4:16 PM Matthew Wilcox <willy@infradead.org> 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/20200625113122.7540-7-willy@infradead.org/
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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

[Paul E. McKenney]

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 <paulmck@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Cc: linux-mm@kvack.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Qian Cai <cai@lca.pw>
> Cc: linux-xfs@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Nice!!!

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  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
>