mm/hmm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

We should not have two different error codes for the same
condition. EAGAIN must be reserved for the FAULT_FLAG_ALLOW_RETRY retry
case and signals to the caller that the mmap_sem has been unlocked.

Use EBUSY for the !valid case so that callers can get the locking right.

Link: https://lore.kernel.org/r/20190724065258.16603-2-hch@lst.de
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
[jgg: elaborated commit message]
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 7d90964..710ce1c 100644 (file)
--- 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 e1eedef..16b6731 100644 (file)
--- 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                /* If range is no longer valid force retry.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                /* If range is no longer valid force retry.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))