Nouveau - Jul 2019 - [PATCH 5/6] nouveau: return -EBUSY when hmm_range_wait_until_valid fails

Hi Jérôme, Ben and Jason,

below is a series against the hmm tree which fixes up the mmap_sem
locking in nouveau and while at it also removes leftover legacy HMM APIs
only used by nouveau.

The first 4 patches are a bug fix for nouveau, which I suspect should
go into this merge window even if the code is marked as staging, just
to avoid people copying the breakage.

Changes since v1:
 - don't return the valid state from hmm_range_unregister
 - additional nouveau cleanups

We should not have two different error codes for the same condition.  In
addition this really complicates the code due to the special handling of
EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
in the core vm.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
---
 Documentation/vm/hmm.rst |  2 +-
 mm/hmm.c                 | 10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 7d90964abbb0..710ce1c701bf 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -237,7 +237,7 @@ The usage pattern is::
       ret = hmm_range_snapshot(&range);
       if (ret) {
           up_read(&mm->mmap_sem);
-          if (ret == -EAGAIN) {
+          if (ret == -EBUSY) {
             /*
              * No need to check hmm_range_wait_until_valid() return value
              * on retry we will get proper error with hmm_range_snapshot()
diff --git a/mm/hmm.c b/mm/hmm.c
index e1eedef129cf..16b6731a34db 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -946,7 +946,7 @@ EXPORT_SYMBOL(hmm_range_unregister);
  * @range: range
  * Return: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
  *          permission (for instance asking for write and range is read only),
- *          -EAGAIN if you need to retry, -EFAULT invalid (ie either no valid
+ *          -EBUSY if you need to retry, -EFAULT invalid (ie either no valid
  *          vma or it is illegal to access that range), number of valid pages
  *          in range->pfns[] (from range start address).
  *
@@ -967,7 +967,7 @@ long hmm_range_snapshot(struct hmm_range *range)
 	do {
 		/* If range is no longer valid force retry. */
 		if (!range->valid)
-			return -EAGAIN;
+			return -EBUSY;
 
 		vma = find_vma(hmm->mm, start);
 		if (vma == NULL || (vma->vm_flags & device_vma))
@@ -1062,10 +1062,8 @@ long hmm_range_fault(struct hmm_range *range, bool block)
 
 	do {
 		/* If range is no longer valid force retry. */
-		if (!range->valid) {
-			up_read(&hmm->mm->mmap_sem);
-			return -EAGAIN;
-		}
+		if (!range->valid)
+			return -EBUSY;
 
 		vma = find_vma(hmm->mm, start);
 		if (vma == NULL || (vma->vm_flags & device_vma))
-- 
2.20.1

These two functions are marked as a legacy APIs to get rid of, but seem
to suit the current nouveau flow.  Move it to the only user in
preparation for fixing a locking bug involving caller and callee.
All comments referring to the old API have been removed as this now
is a driver private helper.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 45 +++++++++++++++++++++-
 include/linux/hmm.h                   | 54 ---------------------------
 2 files changed, 43 insertions(+), 56 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 8c92374afcf2..cde09003c06b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -475,6 +475,47 @@ nouveau_svm_fault_cache(struct nouveau_svm *svm,
 		fault->inst, fault->addr, fault->access);
 }
 
+static inline bool nouveau_range_done(struct hmm_range *range)
+{
+	bool ret = hmm_range_valid(range);
+
+	hmm_range_unregister(range);
+	return ret;
+}
+
+static int
+nouveau_range_fault(struct hmm_mirror *mirror, struct hmm_range *range,
+		    bool block)
+{
+	long ret;
+
+	range->default_flags = 0;
+	range->pfn_flags_mask = -1UL;
+
+	ret = hmm_range_register(range, mirror,
+				 range->start, range->end,
+				 PAGE_SHIFT);
+	if (ret)
+		return (int)ret;
+
+	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
+		up_read(&range->vma->vm_mm->mmap_sem);
+		return -EAGAIN;
+	}
+
+	ret = hmm_range_fault(range, block);
+	if (ret <= 0) {
+		if (ret == -EBUSY || !ret) {
+			up_read(&range->vma->vm_mm->mmap_sem);
+			ret = -EBUSY;
+		} else if (ret == -EAGAIN)
+			ret = -EBUSY;
+		hmm_range_unregister(range);
+		return ret;
+	}
+	return 0;
+}
+
 static int
 nouveau_svm_fault(struct nvif_notify *notify)
 {
@@ -649,10 +690,10 @@ nouveau_svm_fault(struct nvif_notify *notify)
 		range.values = nouveau_svm_pfn_values;
 		range.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT;
 again:
-		ret = hmm_vma_fault(&svmm->mirror, &range, true);
+		ret = nouveau_range_fault(&svmm->mirror, &range, true);
 		if (ret == 0) {
 			mutex_lock(&svmm->mutex);
-			if (!hmm_vma_range_done(&range)) {
+			if (!nouveau_range_done(&range)) {
 				mutex_unlock(&svmm->mutex);
 				goto again;
 			}
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index b8a08b2a10ca..7ef56dc18050 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -484,60 +484,6 @@ long hmm_range_dma_unmap(struct hmm_range *range,
  */
 #define HMM_RANGE_DEFAULT_TIMEOUT 1000
 
-/* This is a temporary helper to avoid merge conflict between trees. */
-static inline bool hmm_vma_range_done(struct hmm_range *range)
-{
-	bool ret = hmm_range_valid(range);
-
-	hmm_range_unregister(range);
-	return ret;
-}
-
-/* This is a temporary helper to avoid merge conflict between trees. */
-static inline int hmm_vma_fault(struct hmm_mirror *mirror,
-				struct hmm_range *range, bool block)
-{
-	long ret;
-
-	/*
-	 * With the old API the driver must set each individual entries with
-	 * the requested flags (valid, write, ...). So here we set the mask to
-	 * keep intact the entries provided by the driver and zero out the
-	 * default_flags.
-	 */
-	range->default_flags = 0;
-	range->pfn_flags_mask = -1UL;
-
-	ret = hmm_range_register(range, mirror,
-				 range->start, range->end,
-				 PAGE_SHIFT);
-	if (ret)
-		return (int)ret;
-
-	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
-		/*
-		 * The mmap_sem was taken by driver we release it here and
-		 * returns -EAGAIN which correspond to mmap_sem have been
-		 * drop in the old API.
-		 */
-		up_read(&range->vma->vm_mm->mmap_sem);
-		return -EAGAIN;
-	}
-
-	ret = hmm_range_fault(range, block);
-	if (ret <= 0) {
-		if (ret == -EBUSY || !ret) {
-			/* Same as above, drop mmap_sem to match old API. */
-			up_read(&range->vma->vm_mm->mmap_sem);
-			ret = -EBUSY;
-		} else if (ret == -EAGAIN)
-			ret = -EBUSY;
-		hmm_range_unregister(range);
-		return ret;
-	}
-	return 0;
-}
-
 /* Below are for HMM internal use only! Not to be used by device driver! */
 static inline void hmm_mm_init(struct mm_struct *mm)
 {
-- 
2.20.1

The parameter is always false, so remove it as well as the -EAGAIN
handling that can only happen for the non-blocking case.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index cde09003c06b..5dd83a46578f 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -484,8 +484,7 @@ static inline bool nouveau_range_done(struct hmm_range
*range)
 }
 
 static int
-nouveau_range_fault(struct hmm_mirror *mirror, struct hmm_range *range,
-		    bool block)
+nouveau_range_fault(struct hmm_mirror *mirror, struct hmm_range *range)
 {
 	long ret;
 
@@ -503,7 +502,7 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range,
 		return -EAGAIN;
 	}
 
-	ret = hmm_range_fault(range, block);
+	ret = hmm_range_fault(range, true);
 	if (ret <= 0) {
 		if (ret == -EBUSY || !ret) {
 			up_read(&range->vma->vm_mm->mmap_sem);
@@ -690,7 +689,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
 		range.values = nouveau_svm_pfn_values;
 		range.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT;
 again:
-		ret = nouveau_range_fault(&svmm->mirror, &range, true);
+		ret = nouveau_range_fault(&svmm->mirror, &range);
 		if (ret == 0) {
 			mutex_lock(&svmm->mutex);
 			if (!nouveau_range_done(&range)) {
-- 
2.20.1

Currently nouveau_svm_fault expects nouveau_range_fault to never unlock
mmap_sem, but the latter unlocks it for a random selection of error
codes. Fix this up by always unlocking mmap_sem for non-zero return
values in nouveau_range_fault, and only unlocking it in the caller
for successful returns.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 5dd83a46578f..5de2d54b9782 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -494,8 +494,10 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
 	ret = hmm_range_register(range, mirror,
 				 range->start, range->end,
 				 PAGE_SHIFT);
-	if (ret)
+	if (ret) {
+		up_read(&range->vma->vm_mm->mmap_sem);
 		return (int)ret;
+	}
 
 	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
 		up_read(&range->vma->vm_mm->mmap_sem);
@@ -504,11 +506,9 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
 
 	ret = hmm_range_fault(range, true);
 	if (ret <= 0) {
-		if (ret == -EBUSY || !ret) {
-			up_read(&range->vma->vm_mm->mmap_sem);
-			ret = -EBUSY;
-		} else if (ret == -EAGAIN)
+		if (ret == 0)
 			ret = -EBUSY;
+		up_read(&range->vma->vm_mm->mmap_sem);
 		hmm_range_unregister(range);
 		return ret;
 	}
@@ -706,8 +706,8 @@ nouveau_svm_fault(struct nvif_notify *notify)
 						NULL);
 			svmm->vmm->vmm.object.client->super = false;
 			mutex_unlock(&svmm->mutex);
+			up_read(&svmm->mm->mmap_sem);
 		}
-		up_read(&svmm->mm->mmap_sem);
 
 		/* Cancel any faults in the window whose pages didn't manage
 		 * to keep their valid bit, or stay writeable when required.
-- 
2.20.1

-EAGAIN has a magic meaning for non-blocking faults, so don't overload
it.  Given that the caller doesn't check for specific error codes this
change is purely cosmetic.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 5de2d54b9782..a9c5c58d425b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -501,7 +501,7 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
 
 	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
 		up_read(&range->vma->vm_mm->mmap_sem);
-		return -EAGAIN;
+		return -EBUSY;
 	}
 
 	ret = hmm_range_fault(range, true);
-- 
2.20.1

Switch the one remaining user in nouveau over to its replacement,
and remove all the wrappers.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>
---
 drivers/gpu/drm/nouveau/nouveau_dmem.c |  2 +-
 include/linux/hmm.h                    | 34 --------------------------
 2 files changed, 1 insertion(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 1333220787a1..345c63cb752a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -845,7 +845,7 @@ nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
 		struct page *page;
 		uint64_t addr;
 
-		page = hmm_pfn_to_page(range, range->pfns[i]);
+		page = hmm_device_entry_to_page(range, range->pfns[i]);
 		if (page == NULL)
 			continue;
 
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 7ef56dc18050..9f32586684c9 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -290,40 +290,6 @@ static inline uint64_t hmm_device_entry_from_pfn(const
struct hmm_range *range,
 		range->flags[HMM_PFN_VALID];
 }
 
-/*
- * Old API:
- * hmm_pfn_to_page()
- * hmm_pfn_to_pfn()
- * hmm_pfn_from_page()
- * hmm_pfn_from_pfn()
- *
- * This are the OLD API please use new API, it is here to avoid cross-tree
- * merge painfullness ie we convert things to new API in stages.
- */
-static inline struct page *hmm_pfn_to_page(const struct hmm_range *range,
-					   uint64_t pfn)
-{
-	return hmm_device_entry_to_page(range, pfn);
-}
-
-static inline unsigned long hmm_pfn_to_pfn(const struct hmm_range *range,
-					   uint64_t pfn)
-{
-	return hmm_device_entry_to_pfn(range, pfn);
-}
-
-static inline uint64_t hmm_pfn_from_page(const struct hmm_range *range,
-					 struct page *page)
-{
-	return hmm_device_entry_from_page(range, page);
-}
-
-static inline uint64_t hmm_pfn_from_pfn(const struct hmm_range *range,
-					unsigned long pfn)
-{
-	return hmm_device_entry_from_pfn(range, pfn);
-}
-
 /*
  * Mirroring: how to synchronize device page table with CPU page table.
  *
-- 
2.20.1

On Mon, Jul 22, 2019 at 3:14 PM Christoph Hellwig <hch at lst.de>
wrote:
>
> We should not have two different error codes for the same condition.  In
> addition this really complicates the code due to the special handling of
> EAGAIN that drops the mmap_sem due to the FAULT_FLAG_ALLOW_RETRY logic
> in the core vm.
>
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Ralph Campbell <rcampbell at nvidia.com>
> Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>
> ---
>  Documentation/vm/hmm.rst |  2 +-
>  mm/hmm.c                 | 10 ++++------
>  2 files changed, 5 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
> index 7d90964abbb0..710ce1c701bf 100644
> --- a/Documentation/vm/hmm.rst
> +++ b/Documentation/vm/hmm.rst
> @@ -237,7 +237,7 @@ The usage pattern is::
>        ret = hmm_range_snapshot(&range);
>        if (ret) {
>            up_read(&mm->mmap_sem);
> -          if (ret == -EAGAIN) {
> +          if (ret == -EBUSY) {
>              /*
>               * No need to check hmm_range_wait_until_valid() return value
>               * on retry we will get proper error with hmm_range_snapshot()
> diff --git a/mm/hmm.c b/mm/hmm.c
> index e1eedef129cf..16b6731a34db 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -946,7 +946,7 @@ EXPORT_SYMBOL(hmm_range_unregister);
>   * @range: range
>   * Return: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM
invalid
>   *          permission (for instance asking for write and range is read
only),
> - *          -EAGAIN if you need to retry, -EFAULT invalid (ie either no
valid
> + *          -EBUSY if you need to retry, -EFAULT invalid (ie either no
valid
>   *          vma or it is illegal to access that range), number of valid
pages
>   *          in range->pfns[] (from range start address).
>   *
> @@ -967,7 +967,7 @@ long hmm_range_snapshot(struct hmm_range *range)
>         do {
>                 /* If range is no longer valid force retry. */
>                 if (!range->valid)
> -                       return -EAGAIN;
> +                       return -EBUSY;
>
>                 vma = find_vma(hmm->mm, start);
>                 if (vma == NULL || (vma->vm_flags & device_vma))
> @@ -1062,10 +1062,8 @@ long hmm_range_fault(struct hmm_range *range, bool
block)
>
>         do {
>                 /* If range is no longer valid force retry. */
> -               if (!range->valid) {
> -                       up_read(&hmm->mm->mmap_sem);
> -                       return -EAGAIN;
> -               }
> +               if (!range->valid)
> +                       return -EBUSY;
Is it fine to remove  up_read(&hmm->mm->mmap_sem) ?
>
>                 vma = find_vma(hmm->mm, start);
>                 if (vma == NULL || (vma->vm_flags & device_vma))
> --
> 2.20.1
>

On 7/22/19 2:44 AM, Christoph Hellwig wrote:
> Hi Jérôme, Ben and Jason,
> 
> below is a series against the hmm tree which fixes up the mmap_sem
> locking in nouveau and while at it also removes leftover legacy HMM APIs
> only used by nouveau.
> 
> The first 4 patches are a bug fix for nouveau, which I suspect should
> go into this merge window even if the code is marked as staging, just
> to avoid people copying the breakage.
> 
> Changes since v1:
>   - don't return the valid state from hmm_range_unregister
>   - additional nouveau cleanups
> 
I ran some OpenCL tests from Jerome with nouveau and this series,
5.3.0-rc1, and my two HMM fixes:
("mm/hmm: fix ZONE_DEVICE anon page mapping reuse")
("mm/hmm: Fix bad subpage pointer in try_to_unmap_one")

You can add for the series:
Tested-by: Ralph Campbell <rcampbell at nvidia.com>

On Mon, Jul 22, 2019 at 11:44:22AM +0200, Christoph Hellwig
wrote:
> These two functions are marked as a legacy APIs to get rid of, but seem
> to suit the current nouveau flow.  Move it to the only user in
> preparation for fixing a locking bug involving caller and callee.
> All comments referring to the old API have been removed as this now
> is a driver private helper.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 45 +++++++++++++++++++++-
>  include/linux/hmm.h                   | 54 ---------------------------
>  2 files changed, 43 insertions(+), 56 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Jason

On Mon, Jul 22, 2019 at 11:44:23AM +0200, Christoph Hellwig
wrote:
> The parameter is always false, so remove it as well as the -EAGAIN
> handling that can only happen for the non-blocking case.
? Did the EAGAIN handling get removed in this patch?
> Signed-off-by: Christoph Hellwig <hch at lst.de>
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
Code seems fine

Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Jason

On Mon, Jul 22, 2019 at 11:44:24AM +0200, Christoph Hellwig
wrote:
> Currently nouveau_svm_fault expects nouveau_range_fault to never unlock
> mmap_sem, but the latter unlocks it for a random selection of error
> codes. Fix this up by always unlocking mmap_sem for non-zero return
> values in nouveau_range_fault, and only unlocking it in the caller
> for successful returns.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index 5dd83a46578f..5de2d54b9782 100644
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -494,8 +494,10 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
>  	ret = hmm_range_register(range, mirror,
>  				 range->start, range->end,
>  				 PAGE_SHIFT);
> -	if (ret)
> +	if (ret) {
> +		up_read(&range->vma->vm_mm->mmap_sem);
>  		return (int)ret;
> +	}
>  
>  	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
>  		up_read(&range->vma->vm_mm->mmap_sem);
> @@ -504,11 +506,9 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
>  
>  	ret = hmm_range_fault(range, true);
>  	if (ret <= 0) {
> -		if (ret == -EBUSY || !ret) {
> -			up_read(&range->vma->vm_mm->mmap_sem);
> -			ret = -EBUSY;
> -		} else if (ret == -EAGAIN)
> +		if (ret == 0)
>  			ret = -EBUSY;
> +		up_read(&range->vma->vm_mm->mmap_sem);
>  		hmm_range_unregister(range);
>  		return ret;
Hum..

The caller does this:

again:
		ret = nouveau_range_fault(&svmm->mirror, &range);
		if (ret == 0) {
			mutex_lock(&svmm->mutex);
			if (!nouveau_range_done(&range)) {
				mutex_unlock(&svmm->mutex);
				goto again;

And we can't call nouveau_range_fault() -> hmm_range_fault() without
holding the mmap_sem, so we can't allow nouveau_range_fault to unlock
it.

Maybe this instead? 

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index a9c5c58d425b3d..92cf760a9bcc5d 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -494,21 +494,16 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct
hmm_range *range)
 	ret = hmm_range_register(range, mirror,
 				 range->start, range->end,
 				 PAGE_SHIFT);
-	if (ret) {
-		up_read(&range->vma->vm_mm->mmap_sem);
+	if (ret)
 		return (int)ret;
-	}
 
-	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
-		up_read(&range->vma->vm_mm->mmap_sem);
+	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT))
 		return -EBUSY;
-	}
 
 	ret = hmm_range_fault(range, true);
 	if (ret <= 0) {
 		if (ret == 0)
 			ret = -EBUSY;
-		up_read(&range->vma->vm_mm->mmap_sem);
 		hmm_range_unregister(range);
 		return ret;
 	}
@@ -706,8 +701,8 @@ nouveau_svm_fault(struct nvif_notify *notify)
 						NULL);
 			svmm->vmm->vmm.object.client->super = false;
 			mutex_unlock(&svmm->mutex);
-			up_read(&svmm->mm->mmap_sem);
 		}
+		up_read(&svmm->mm->mmap_sem);
 
 		/* Cancel any faults in the window whose pages didn't manage
 		 * to keep their valid bit, or stay writeable when required.

On Mon, Jul 22, 2019 at 11:44:25AM +0200, Christoph Hellwig
wrote:
> -EAGAIN has a magic meaning for non-blocking faults, so don't overload
> it.  Given that the caller doesn't check for specific error codes this
> change is purely cosmetic.
> 
> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>  drivers/gpu/drm/nouveau/nouveau_svm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
Agree

Reviewed-by: Jason Gunthorpe <jgg at mellanox.com>

Jason

On Mon, Jul 22, 2019 at 06:11:04PM -0700, Ralph Campbell
wrote:
> 
> On 7/22/19 2:44 AM, Christoph Hellwig wrote:
> > Hi Jérôme, Ben and Jason,
> > 
> > below is a series against the hmm tree which fixes up the mmap_sem
> > locking in nouveau and while at it also removes leftover legacy HMM
APIs
> > only used by nouveau.
> > 
> > The first 4 patches are a bug fix for nouveau, which I suspect should
> > go into this merge window even if the code is marked as staging, just
> > to avoid people copying the breakage.
> > 
> > Changes since v1:
> >   - don't return the valid state from hmm_range_unregister
> >   - additional nouveau cleanups
> > 
> 
> I ran some OpenCL tests from Jerome with nouveau and this series,
> 5.3.0-rc1, and my two HMM fixes:
> ("mm/hmm: fix ZONE_DEVICE anon page mapping reuse")
> ("mm/hmm: Fix bad subpage pointer in try_to_unmap_one")
> 
> You can add for the series:
> Tested-by: Ralph Campbell <rcampbell at nvidia.com>
Thanks, would you also rebase and resend the patch deleting 
struct hmm_update ?

Jason

On Mon, Jul 22, 2019 at 11:44:20AM +0200, Christoph Hellwig
wrote:
> Hi Jérôme, Ben and Jason,
> 
> below is a series against the hmm tree which fixes up the mmap_sem
> locking in nouveau and while at it also removes leftover legacy HMM APIs
> only used by nouveau.
> 
> The first 4 patches are a bug fix for nouveau, which I suspect should
> go into this merge window even if the code is marked as staging, just
> to avoid people copying the breakage.
Ignoring the STAGING issue I've tried to use the same guideline as for
-stable for -rc .. 

So this is a real problem, we definitely hit the locking bugs if we
retry/etc under stress, so I would be OK to send it to Linus for
early-rc.

However, it doesn't look like the 1st patch is fixing a current bug
though, the only callers uses blocking = true, so just the middle
three are -rc?

Thanks,
Jason

On Tue, Jul 23, 2019 at 03:27:41PM +0000, Jason Gunthorpe
wrote:
> Ignoring the STAGING issue I've tried to use the same guideline as for
> -stable for -rc .. 
> 
> So this is a real problem, we definitely hit the locking bugs if we
> retry/etc under stress, so I would be OK to send it to Linus for
> early-rc.
> 
> However, it doesn't look like the 1st patch is fixing a current bug
> though, the only callers uses blocking = true, so just the middle
> three are -rc?
nonblocking isn't used anywher, but it is a major, major API bug.
Your call, but if it was my tree I'd probably send it to Linus.