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Subject[PATCH AUTOSEL 5.2 10/59] mm/hmm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}
Date
From: Christoph Hellwig <hch@lst.de>

[ Upstream commit 2bcbeaefde2f0384d6ad351c151b1a9fe7791a0a ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 7cdf7282e0229..65b6c1109cc81 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -231,7 +231,7 @@ respect in order to keep things properly synchronized. 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 4c405dfbd2b3d..27dd9a8816272 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -995,7 +995,7 @@ EXPORT_SYMBOL(hmm_range_unregister);
* @range: range
* Returns: -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).
*
@@ -1019,7 +1019,7 @@ 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/* If range is no longer valid force retry.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))
@@ -1117,10 +1117,8 @@ 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
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