linux-kernel - [PATCH AUTOSEL 5.2 10/59] mm/hmm: always return EBUSY for invalid ranges in hmm_range

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Date:   Tue,  6 Aug 2019 17:32:30 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Christoph Hellwig <hch@....de>,
        Ralph Campbell <rcampbell@...dia.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Sasha Levin <sashal@...nel.org>, linux-mm@...ck.org,
        linux-doc@...r.kernel.org
Subject: [PATCH AUTOSEL 5.2 10/59] mm/hmm: always return EBUSY for invalid ranges in hmm_range_{fault,snapshot}

From: Christoph Hellwig <hch@....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@...dia.com>
Signed-off-by: Christoph Hellwig <hch@....de>
Reviewed-by: Ralph Campbell <rcampbell@...dia.com>
Reviewed-by: Jason Gunthorpe <jgg@...lanox.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@....com>
[jgg: elaborated commit message]
Signed-off-by: Jason Gunthorpe <jgg@...lanox.com>
Signed-off-by: Sasha Levin <sashal@...nel.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