[PATCH 0/3] mmu_notifier fs fs_reclaim lockdep annotations

[PATCH 0/3] mmu_notifier fs fs_reclaim lockdep annotations

[Daniel Vetter]

Hi all,

I've finally gotten around to polish of my lockdep anntotation patches
from a while ago:

https://lore.kernel.org/dri-devel/20200610194101.1668038-1-daniel.vetter@ffwll.ch/

That patch has been in -mm for a few days already, but it immediately hit
some issues with xfs.

Changes since v2:
- Now hopefully the bug that bombed xfs fixed.
- With unit-tests (that's the part I really wanted and never got to)
- might_alloc() helper thrown in for good.

The unit test stuff was the major drag until I figured out how to make
this very easy with the locking selftests.

Comments, review, testing all very much welcome.

Cheers, Daniel

Daniel Vetter (3):
  mm: Track mmu notifiers in fs_reclaim_acquire/release
  mm: Extract might_alloc() debug check
  locking/selftests: Add testcases for fs_reclaim

 include/linux/sched/mm.h | 16 ++++++++++++++
 lib/locking-selftest.c   | 47 ++++++++++++++++++++++++++++++++++++++++
 mm/mmu_notifier.c        |  7 ------
 mm/page_alloc.c          | 31 ++++++++++++++++----------
 mm/slab.h                |  5 +----
 mm/slob.c                |  6 ++---
 6 files changed, 86 insertions(+), 26 deletions(-)

-- 
2.29.2

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[PATCH 1/3] 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>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
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 5654dd19addc..61ee40ed804e 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 23f5066bd4a5..ff0f9a84b8de 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>
@@ -4264,10 +4265,8 @@ 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;
@@ -4276,10 +4275,6 @@ 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;
 
@@ -4298,15 +4293,29 @@ 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
-- 
2.29.2

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Re: [PATCH 1/3] mm: Track mmu notifiers in fs_reclaim_acquire/release

[Jason Gunthorpe]

On Fri, Nov 20, 2020 at 10:54:42AM +0100, Daniel Vetter wrote:
> 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>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> 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(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason
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[PATCH 2/3] 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. Willy is working on a patch series
which might change this:

https://lore.kernel.org/linux-mm/20200625113122.7540-7-willy@infradead.org/

I think best would be if that updates gfpflags_allow_blocking(), since
there's a ton of callers all over the place for that already.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
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
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.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 d5ece7a9a403..f94405d43fd1 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -180,6 +180,22 @@ 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 6d7c6a5056ba..37b981247e5d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -500,10 +500,7 @@ 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);
-- 
2.29.2

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Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Randy Dunlap]

Hi,

On 11/20/20 1:54 AM, Daniel Vetter wrote:
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index d5ece7a9a403..f94405d43fd1 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -180,6 +180,22 @@ 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

                    Mark

> + * @gfp_mask: gfp_t flags that would be use to allocate

                                           used

> + *
> + * Similar to might_sleep() and other annotations this can be used in functions

                                         annotations,

> + * that might allocate, but often dont. Compiles to nothing without

                                     don't.

> + * CONFIG_LOCKDEP. Includes a conditional might_sleep() if @gfp allows blocking.

?                                            might_sleep_if() if

> + */
> +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));
> +}


-- 
~Randy

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Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Daniel Vetter]

On Fri, Nov 20, 2020 at 6:20 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> Hi,
>
> On 11/20/20 1:54 AM, Daniel Vetter wrote:
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index d5ece7a9a403..f94405d43fd1 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -180,6 +180,22 @@ 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
>
>                     Mark
>
> > + * @gfp_mask: gfp_t flags that would be use to allocate
>
>                                            used
>
> > + *
> > + * Similar to might_sleep() and other annotations this can be used in functions
>
>                                          annotations,
>
> > + * that might allocate, but often dont. Compiles to nothing without
>
>                                      don't.
>
> > + * CONFIG_LOCKDEP. Includes a conditional might_sleep() if @gfp allows blocking.
>
> ?                                            might_sleep_if() if

That's one if too many, I'll do the others for next round. Thanks for
taking a look.
-Daniel

>
> > + */
> > +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));
> > +}
>
>
> --
> ~Randy
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Jason Gunthorpe]

On Fri, Nov 20, 2020 at 10:54:43AM +0100, Daniel Vetter wrote:
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index d5ece7a9a403..f94405d43fd1 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -180,6 +180,22 @@ 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));
> +}

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Oh, I just had a another thread with Matt about xarray, this would be
perfect to add before xas_nomem():

diff --git a/lib/idr.c b/lib/idr.c
index f4ab4f4aa3c7f5..722d9ddff53221 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -391,6 +391,8 @@ int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
 	if ((int)max < 0)
 		max = INT_MAX;
 
+	might_alloc(gfp);
+
 retry:
 	xas_lock_irqsave(&xas, flags);
 next:
diff --git a/lib/xarray.c b/lib/xarray.c
index 5fa51614802ada..dd260ee7dcae9a 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1534,6 +1534,8 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return XA_ERROR(-EINVAL);
 	if (xa_track_free(xa) && !entry)
@@ -1600,6 +1602,8 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return XA_ERROR(-EINVAL);
 
@@ -1637,6 +1641,8 @@ int __xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
 	XA_STATE(xas, xa, index);
 	void *curr;
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return -EINVAL;
 	if (!entry)
@@ -1806,6 +1812,8 @@ int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
 {
 	XA_STATE(xas, xa, 0);
 
+	might_alloc(gfp);
+
 	if (WARN_ON_ONCE(xa_is_advanced(entry)))
 		return -EINVAL;
 	if (WARN_ON_ONCE(!xa_track_free(xa)))
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Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Daniel Vetter]

On Fri, Nov 20, 2020 at 02:07:19PM -0400, Jason Gunthorpe wrote:
> On Fri, Nov 20, 2020 at 10:54:43AM +0100, Daniel Vetter wrote:
> > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > index d5ece7a9a403..f94405d43fd1 100644
> > --- a/include/linux/sched/mm.h
> > +++ b/include/linux/sched/mm.h
> > @@ -180,6 +180,22 @@ 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));
> > +}
> 
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> 
> Oh, I just had a another thread with Matt about xarray, this would be
> perfect to add before xas_nomem():

Yeah I think there's plenty of places where this will be useful. Want to
slap a sob onto this diff so I can include it for the next round, or will
you or Matt send this out when my might_alloc has landed?
-Daniel

> 
> diff --git a/lib/idr.c b/lib/idr.c
> index f4ab4f4aa3c7f5..722d9ddff53221 100644
> --- a/lib/idr.c
> +++ b/lib/idr.c
> @@ -391,6 +391,8 @@ int ida_alloc_range(struct ida *ida, unsigned int min, unsigned int max,
>  	if ((int)max < 0)
>  		max = INT_MAX;
>  
> +	might_alloc(gfp);
> +
>  retry:
>  	xas_lock_irqsave(&xas, flags);
>  next:
> diff --git a/lib/xarray.c b/lib/xarray.c
> index 5fa51614802ada..dd260ee7dcae9a 100644
> --- a/lib/xarray.c
> +++ b/lib/xarray.c
> @@ -1534,6 +1534,8 @@ void *__xa_store(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
>  	XA_STATE(xas, xa, index);
>  	void *curr;
>  
> +	might_alloc(gfp);
> +
>  	if (WARN_ON_ONCE(xa_is_advanced(entry)))
>  		return XA_ERROR(-EINVAL);
>  	if (xa_track_free(xa) && !entry)
> @@ -1600,6 +1602,8 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
>  	XA_STATE(xas, xa, index);
>  	void *curr;
>  
> +	might_alloc(gfp);
> +
>  	if (WARN_ON_ONCE(xa_is_advanced(entry)))
>  		return XA_ERROR(-EINVAL);
>  
> @@ -1637,6 +1641,8 @@ int __xa_insert(struct xarray *xa, unsigned long index, void *entry, gfp_t gfp)
>  	XA_STATE(xas, xa, index);
>  	void *curr;
>  
> +	might_alloc(gfp);
> +
>  	if (WARN_ON_ONCE(xa_is_advanced(entry)))
>  		return -EINVAL;
>  	if (!entry)
> @@ -1806,6 +1812,8 @@ int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
>  {
>  	XA_STATE(xas, xa, 0);
>  
> +	might_alloc(gfp);
> +
>  	if (WARN_ON_ONCE(xa_is_advanced(entry)))
>  		return -EINVAL;
>  	if (WARN_ON_ONCE(!xa_track_free(xa)))

-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH 2/3] mm: Extract might_alloc() debug check

[Jason Gunthorpe]

On Tue, Nov 24, 2020 at 03:34:11PM +0100, Daniel Vetter wrote:
> On Fri, Nov 20, 2020 at 02:07:19PM -0400, Jason Gunthorpe wrote:
> > On Fri, Nov 20, 2020 at 10:54:43AM +0100, Daniel Vetter wrote:
> > > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> > > index d5ece7a9a403..f94405d43fd1 100644
> > > +++ b/include/linux/sched/mm.h
> > > @@ -180,6 +180,22 @@ 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));
> > > +}
> > 
> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> > 
> > Oh, I just had a another thread with Matt about xarray, this would be
> > perfect to add before xas_nomem():
> 
> Yeah I think there's plenty of places where this will be useful. Want to
> slap a sob onto this diff so I can include it for the next round, or will
> you or Matt send this out when my might_alloc has landed?

When this is merged I can do this - just wanted to point out the API
is good and useful

Jason
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[PATCH 3/3] locking/selftests: Add testcases for fs_reclaim

[Daniel Vetter]

Since I butchered this I figured better to make sure we have testcases
for this now. Since we only have a locking context for __GFP_FS that's
the only thing we're testing right now.

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>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
 lib/locking-selftest.c | 47 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index a899b3f0e2e5..ad47c3358e30 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -15,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/ww_mutex.h>
 #include <linux/sched.h>
+#include <linux/sched/mm.h>
 #include <linux/delay.h>
 #include <linux/lockdep.h>
 #include <linux/spinlock.h>
@@ -2357,6 +2358,50 @@ static void queued_read_lock_tests(void)
 	pr_cont("\n");
 }
 
+static void fs_reclaim_correct_nesting(void)
+{
+	fs_reclaim_acquire(GFP_KERNEL);
+	might_alloc(GFP_NOFS);
+	fs_reclaim_release(GFP_KERNEL);
+}
+
+static void fs_reclaim_wrong_nesting(void)
+{
+	fs_reclaim_acquire(GFP_KERNEL);
+	might_alloc(GFP_KERNEL);
+	fs_reclaim_release(GFP_KERNEL);
+}
+
+static void fs_reclaim_protected_nesting(void)
+{
+	unsigned int flags;
+
+	fs_reclaim_acquire(GFP_KERNEL);
+	flags = memalloc_nofs_save();
+	might_alloc(GFP_KERNEL);
+	memalloc_nofs_restore(flags);
+	fs_reclaim_release(GFP_KERNEL);
+}
+
+static void fs_reclaim_tests(void)
+{
+	printk("  --------------------\n");
+	printk("  | fs_reclaim tests |\n");
+	printk("  --------------------\n");
+
+	print_testname("correct nesting");
+	dotest(fs_reclaim_correct_nesting, SUCCESS, 0);
+	pr_cont("\n");
+
+	print_testname("wrong nesting");
+	dotest(fs_reclaim_wrong_nesting, FAILURE, 0);
+	pr_cont("\n");
+
+	print_testname("protected nesting");
+	dotest(fs_reclaim_protected_nesting, SUCCESS, 0);
+	pr_cont("\n");
+}
+
 void locking_selftest(void)
 {
 	/*
@@ -2478,6 +2523,8 @@ void locking_selftest(void)
 	if (IS_ENABLED(CONFIG_QUEUED_RWLOCKS))
 		queued_read_lock_tests();
 
+	fs_reclaim_tests();
+
 	if (unexpected_testcase_failures) {
 		printk("-----------------------------------------------------------------\n");
 		debug_locks = 0;
-- 
2.29.2

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Re: [PATCH 3/3] locking/selftests: Add testcases for fs_reclaim

[Peter Zijlstra]

On Fri, Nov 20, 2020 at 10:54:44AM +0100, Daniel Vetter wrote:
> Since I butchered this I figured better to make sure we have testcases
> for this now. Since we only have a locking context for __GFP_FS that's
> the only thing we're testing right now.
> 
> 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>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: linux-kernel@vger.kernel.org
> ---
>  lib/locking-selftest.c | 47 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)

I have a few changes pending for this file, I don't think the conflicts
will be bad, but..

In any case:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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[PATCH] drm/ttm: don't set page->mapping

[Daniel Vetter]

Random observation while trying to review Christian's patch series to
stop looking at struct page for dma-buf imports.

This was originally added in

commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
Author: Thomas Hellstrom <thellstrom@vmware.com>
Date:   Fri Jan 3 11:47:23 2014 +0100

    drm/ttm: Correctly set page mapping and -index members

    Needed for some vm operations; most notably unmap_mapping_range() with
    even_cows = 0.

    Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
    Reviewed-by: Brian Paul <brianp@vmware.com>

but we do not have a single caller of unmap_mapping_range with
even_cows == 0. And all the gem drivers don't do this, so another
small thing we could standardize between drm and ttm drivers.

Plus I don't really see a need for unamp_mapping_range where we don't
want to indiscriminately shoot down all ptes.

Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Brian Paul <brianp@vmware.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Christian Koenig <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
---
 drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index da9eeffe0c6d..5b2eb6d58bb7 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
 	return ret;
 }
 
-static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
-{
-	pgoff_t i;
-
-	if (ttm->page_flags & TTM_PAGE_FLAG_SG)
-		return;
-
-	for (i = 0; i < ttm->num_pages; ++i)
-		ttm->pages[i]->mapping = bdev->dev_mapping;
-}
-
 int ttm_tt_populate(struct ttm_bo_device *bdev,
 		    struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
 {
@@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
 	if (ret)
 		return ret;
 
-	ttm_tt_add_mapping(bdev, ttm);
 	ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
 	if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
 		ret = ttm_tt_swapin(ttm);
-- 
2.29.2

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Re: [PATCH] drm/ttm: don't set page->mapping

[Christian König]

Am 20.11.20 um 10:54 schrieb Daniel Vetter:
> Random observation while trying to review Christian's patch series to
> stop looking at struct page for dma-buf imports.
>
> This was originally added in
>
> commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
> Author: Thomas Hellstrom <thellstrom@vmware.com>
> Date:   Fri Jan 3 11:47:23 2014 +0100
>
>      drm/ttm: Correctly set page mapping and -index members
>
>      Needed for some vm operations; most notably unmap_mapping_range() with
>      even_cows = 0.
>
>      Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
>      Reviewed-by: Brian Paul <brianp@vmware.com>
>
> but we do not have a single caller of unmap_mapping_range with
> even_cows == 0. And all the gem drivers don't do this, so another
> small thing we could standardize between drm and ttm drivers.
>
> Plus I don't really see a need for unamp_mapping_range where we don't
> want to indiscriminately shoot down all ptes.
>
> Cc: Thomas Hellstrom <thellstrom@vmware.com>
> Cc: Brian Paul <brianp@vmware.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Christian Koenig <christian.koenig@amd.com>
> Cc: Huang Rui <ray.huang@amd.com>

This is still a NAK as long as we can't come up with a better way to 
track TTMs page allocations.

Additional to that page_mapping() is used quite extensively in the mm 
code and I'm not sure if that isn't needed for other stuff as well.

Regards,
Christian.

> ---
>   drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
>   1 file changed, 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index da9eeffe0c6d..5b2eb6d58bb7 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>   	return ret;
>   }
>   
> -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> -{
> -	pgoff_t i;
> -
> -	if (ttm->page_flags & TTM_PAGE_FLAG_SG)
> -		return;
> -
> -	for (i = 0; i < ttm->num_pages; ++i)
> -		ttm->pages[i]->mapping = bdev->dev_mapping;
> -}
> -
>   int ttm_tt_populate(struct ttm_bo_device *bdev,
>   		    struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
>   {
> @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
>   	if (ret)
>   		return ret;
>   
> -	ttm_tt_add_mapping(bdev, ttm);
>   	ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
>   	if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
>   		ret = ttm_tt_swapin(ttm);

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Re: [PATCH] drm/ttm: don't set page->mapping

[Daniel Vetter]

On Fri, Nov 20, 2020 at 11:04 AM Christian König
<christian.koenig@amd.com> wrote:
>
> Am 20.11.20 um 10:54 schrieb Daniel Vetter:
> > Random observation while trying to review Christian's patch series to
> > stop looking at struct page for dma-buf imports.
> >
> > This was originally added in
> >
> > commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
> > Author: Thomas Hellstrom <thellstrom@vmware.com>
> > Date:   Fri Jan 3 11:47:23 2014 +0100
> >
> >      drm/ttm: Correctly set page mapping and -index members
> >
> >      Needed for some vm operations; most notably unmap_mapping_range() with
> >      even_cows = 0.
> >
> >      Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> >      Reviewed-by: Brian Paul <brianp@vmware.com>
> >
> > but we do not have a single caller of unmap_mapping_range with
> > even_cows == 0. And all the gem drivers don't do this, so another
> > small thing we could standardize between drm and ttm drivers.
> >
> > Plus I don't really see a need for unamp_mapping_range where we don't
> > want to indiscriminately shoot down all ptes.
> >
> > Cc: Thomas Hellstrom <thellstrom@vmware.com>
> > Cc: Brian Paul <brianp@vmware.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Christian Koenig <christian.koenig@amd.com>
> > Cc: Huang Rui <ray.huang@amd.com>
>
> This is still a NAK as long as we can't come up with a better way to
> track TTMs page allocations.
>
> Additional to that page_mapping() is used quite extensively in the mm
> code and I'm not sure if that isn't needed for other stuff as well.

Apologies, I'm honestly not quite sure how this lone patch here ended
up in this submission. I didn't want to send it out.
-Daniel

>
> Regards,
> Christian.
>
> > ---
> >   drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
> >   1 file changed, 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> > index da9eeffe0c6d..5b2eb6d58bb7 100644
> > --- a/drivers/gpu/drm/ttm/ttm_tt.c
> > +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> > @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> >       return ret;
> >   }
> >
> > -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> > -{
> > -     pgoff_t i;
> > -
> > -     if (ttm->page_flags & TTM_PAGE_FLAG_SG)
> > -             return;
> > -
> > -     for (i = 0; i < ttm->num_pages; ++i)
> > -             ttm->pages[i]->mapping = bdev->dev_mapping;
> > -}
> > -
> >   int ttm_tt_populate(struct ttm_bo_device *bdev,
> >                   struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
> >   {
> > @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
> >       if (ret)
> >               return ret;
> >
> > -     ttm_tt_add_mapping(bdev, ttm);
> >       ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
> >       if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
> >               ret = ttm_tt_swapin(ttm);
>


-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/ttm: don't set page->mapping

[Christian König]

Am 20.11.20 um 11:05 schrieb Daniel Vetter:
> On Fri, Nov 20, 2020 at 11:04 AM Christian König
> <christian.koenig@amd.com> wrote:
>> Am 20.11.20 um 10:54 schrieb Daniel Vetter:
>>> Random observation while trying to review Christian's patch series to
>>> stop looking at struct page for dma-buf imports.
>>>
>>> This was originally added in
>>>
>>> commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
>>> Author: Thomas Hellstrom <thellstrom@vmware.com>
>>> Date:   Fri Jan 3 11:47:23 2014 +0100
>>>
>>>       drm/ttm: Correctly set page mapping and -index members
>>>
>>>       Needed for some vm operations; most notably unmap_mapping_range() with
>>>       even_cows = 0.
>>>
>>>       Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
>>>       Reviewed-by: Brian Paul <brianp@vmware.com>
>>>
>>> but we do not have a single caller of unmap_mapping_range with
>>> even_cows == 0. And all the gem drivers don't do this, so another
>>> small thing we could standardize between drm and ttm drivers.
>>>
>>> Plus I don't really see a need for unamp_mapping_range where we don't
>>> want to indiscriminately shoot down all ptes.
>>>
>>> Cc: Thomas Hellstrom <thellstrom@vmware.com>
>>> Cc: Brian Paul <brianp@vmware.com>
>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>> Cc: Christian Koenig <christian.koenig@amd.com>
>>> Cc: Huang Rui <ray.huang@amd.com>
>> This is still a NAK as long as we can't come up with a better way to
>> track TTMs page allocations.
>>
>> Additional to that page_mapping() is used quite extensively in the mm
>> code and I'm not sure if that isn't needed for other stuff as well.
> Apologies, I'm honestly not quite sure how this lone patch here ended
> up in this submission. I didn't want to send it out.

No problem.

But looking a bit deeper into the mm code that other drm drivers don't 
set this correctly and still use unmap_mapping_range() sounds like quite 
a bug to me.

Going to track down what exactly that is used for.

Christian.

> -Daniel
>
>> Regards,
>> Christian.
>>
>>> ---
>>>    drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
>>>    1 file changed, 12 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
>>> index da9eeffe0c6d..5b2eb6d58bb7 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_tt.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
>>> @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>>>        return ret;
>>>    }
>>>
>>> -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
>>> -{
>>> -     pgoff_t i;
>>> -
>>> -     if (ttm->page_flags & TTM_PAGE_FLAG_SG)
>>> -             return;
>>> -
>>> -     for (i = 0; i < ttm->num_pages; ++i)
>>> -             ttm->pages[i]->mapping = bdev->dev_mapping;
>>> -}
>>> -
>>>    int ttm_tt_populate(struct ttm_bo_device *bdev,
>>>                    struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
>>>    {
>>> @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
>>>        if (ret)
>>>                return ret;
>>>
>>> -     ttm_tt_add_mapping(bdev, ttm);
>>>        ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
>>>        if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
>>>                ret = ttm_tt_swapin(ttm);
>

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Re: [PATCH] drm/ttm: don't set page->mapping

[Daniel Vetter]

On Fri, Nov 20, 2020 at 11:08:31AM +0100, Christian König wrote:
> Am 20.11.20 um 11:05 schrieb Daniel Vetter:
> > On Fri, Nov 20, 2020 at 11:04 AM Christian König
> > <christian.koenig@amd.com> wrote:
> > > Am 20.11.20 um 10:54 schrieb Daniel Vetter:
> > > > Random observation while trying to review Christian's patch series to
> > > > stop looking at struct page for dma-buf imports.
> > > > 
> > > > This was originally added in
> > > > 
> > > > commit 58aa6622d32af7d2c08d45085f44c54554a16ed7
> > > > Author: Thomas Hellstrom <thellstrom@vmware.com>
> > > > Date:   Fri Jan 3 11:47:23 2014 +0100
> > > > 
> > > >       drm/ttm: Correctly set page mapping and -index members
> > > > 
> > > >       Needed for some vm operations; most notably unmap_mapping_range() with
> > > >       even_cows = 0.
> > > > 
> > > >       Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> > > >       Reviewed-by: Brian Paul <brianp@vmware.com>
> > > > 
> > > > but we do not have a single caller of unmap_mapping_range with
> > > > even_cows == 0. And all the gem drivers don't do this, so another
> > > > small thing we could standardize between drm and ttm drivers.
> > > > 
> > > > Plus I don't really see a need for unamp_mapping_range where we don't
> > > > want to indiscriminately shoot down all ptes.
> > > > 
> > > > Cc: Thomas Hellstrom <thellstrom@vmware.com>
> > > > Cc: Brian Paul <brianp@vmware.com>
> > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > > Cc: Christian Koenig <christian.koenig@amd.com>
> > > > Cc: Huang Rui <ray.huang@amd.com>
> > > This is still a NAK as long as we can't come up with a better way to
> > > track TTMs page allocations.
> > > 
> > > Additional to that page_mapping() is used quite extensively in the mm
> > > code and I'm not sure if that isn't needed for other stuff as well.
> > Apologies, I'm honestly not quite sure how this lone patch here ended
> > up in this submission. I didn't want to send it out.
> 
> No problem.
> 
> But looking a bit deeper into the mm code that other drm drivers don't set
> this correctly and still use unmap_mapping_range() sounds like quite a bug
> to me.
> 
> Going to track down what exactly that is used for.

Pagecache shootdown. unmap_mapping_range only shoots down from the virtual
side. Since that's all we care about, we don't need to set up the
address_space in the page.
-Daniel

> 
> Christian.
> 
> > -Daniel
> > 
> > > Regards,
> > > Christian.
> > > 
> > > > ---
> > > >    drivers/gpu/drm/ttm/ttm_tt.c | 12 ------------
> > > >    1 file changed, 12 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> > > > index da9eeffe0c6d..5b2eb6d58bb7 100644
> > > > --- a/drivers/gpu/drm/ttm/ttm_tt.c
> > > > +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> > > > @@ -284,17 +284,6 @@ int ttm_tt_swapout(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> > > >        return ret;
> > > >    }
> > > > 
> > > > -static void ttm_tt_add_mapping(struct ttm_bo_device *bdev, struct ttm_tt *ttm)
> > > > -{
> > > > -     pgoff_t i;
> > > > -
> > > > -     if (ttm->page_flags & TTM_PAGE_FLAG_SG)
> > > > -             return;
> > > > -
> > > > -     for (i = 0; i < ttm->num_pages; ++i)
> > > > -             ttm->pages[i]->mapping = bdev->dev_mapping;
> > > > -}
> > > > -
> > > >    int ttm_tt_populate(struct ttm_bo_device *bdev,
> > > >                    struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)
> > > >    {
> > > > @@ -313,7 +302,6 @@ int ttm_tt_populate(struct ttm_bo_device *bdev,
> > > >        if (ret)
> > > >                return ret;
> > > > 
> > > > -     ttm_tt_add_mapping(bdev, ttm);
> > > >        ttm->page_flags |= TTM_PAGE_FLAG_PRIV_POPULATED;
> > > >        if (unlikely(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
> > > >                ret = ttm_tt_swapin(ttm);
> > 
> 

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