linux-kernel - [PATCH 2/5] mm: always return EBUSY for invalid ranges in hmm_range

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Date:   Wed,  3 Jul 2019 11:44:59 -0700
From:   Christoph Hellwig <hch@....de>
To:     Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Ben Skeggs <bskeggs@...hat.com>
Cc:     linux-mm@...ck.org, nouveau@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ralph Campbell <rcampbell@...dia.com>,
        Felix Kuehling <Felix.Kuehling@....com>
Subject: [PATCH 2/5] mm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

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@....de>
Reviewed-by: Ralph Campbell <rcampbell@...dia.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@....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 ac238d3f1f4e..3abc2e3c1e9f 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -951,7 +951,7 @@ 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).
  *
@@ -972,7 +972,7 @@ 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 		/* If range is no longer valid force retry.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))
@@ -1067,10 +1067,8 @@ 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