From: Laurent Vivier <lviv...@redhat.com>
[ Upstream commit 45ebc7e6c125ce93d2ddf82cd5bea20121bb0258 ]
The virtqueue_resize() function was not correctly propagating error codes
from its internal resize helper functions, specifically
virtqueue_resize_packet() and virtqueue_resize_split(). If these helpers
returned an error, but the subsequent call to virtqueue_enable_after_reset()
succeeded, the original error from the resize operation would be masked.
Consequently, virtqueue_resize() could incorrectly report success to its
caller despite an underlying resize failure.
This change restores the original code behavior:
if (vdev->config->enable_vq_after_reset(_vq))
return -EBUSY;
return err;
Fix: commit ad48d53b5b3f ("virtio_ring: separate the logic of reset/enable from
virtqueue_resize")
Cc: xuanz...@linux.alibaba.com
Signed-off-by: Laurent Vivier <lviv...@redhat.com>
Acked-by: Jason Wang <jasow...@redhat.com>
Link: https://patch.msgid.link/20250521092236.661410-2-lviv...@redhat.com
Tested-by: Lei Yang <leiy...@redhat.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Paolo Abeni <pab...@redhat.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
## Analysis Summary
**YES**, this commit should be backported to stable kernel trees.
Here's my extensive analysis:
### 1. **This is a clear bug fix for incorrect error reporting**
The commit fixes a critical error handling bug in `virtqueue_resize()`
where error codes from the resize operation (`virtqueue_resize_packed()`
or `virtqueue_resize_split()`) were being masked if
`virtqueue_enable_after_reset()` succeeded.
The specific bug pattern:
```c
// Before fix (buggy code):
err = virtqueue_resize_packed/_split(_vq, num); // May return error
return virtqueue_enable_after_reset(_vq); // Returns 0 on
success, masking 'err'
// After fix (correct code):
err = virtqueue_resize_packed/_split(_vq, num);
err_reset = virtqueue_enable_after_reset(_vq);
if (err_reset)
return err_reset;
return err; // Correctly returns the resize error
```
### 2. **The bug affects users and can cause silent failures**
According to the function documentation at lines 2787-2788, when
`-ENOMEM` is returned from resize, "vq can still work normally" with the
original ring size. However, with the bug, the caller would receive
success (0) instead of `-ENOMEM`, leading them to incorrectly believe
the resize succeeded when it actually failed. This could cause:
- Incorrect assumptions about queue capacity
- Performance issues if the application expected a different queue size
- Potential resource allocation mismatches
### 3. **The fix is small, contained, and low-risk**
The change is minimal - only 6 lines of code:
- Introduces a new local variable `err_reset`
- Properly preserves and returns the original error code
- No architectural changes or new features
- Only affects error propagation logic
### 4. **The bug exists in stable kernels**
- Bug introduced in v6.6-rc1 (commit ad48d53b5b3f)
- The feature (virtqueue_resize) exists since v6.0-rc1
- Therefore, stable kernels 6.6.x and later contain this bug
### 5. **Clear regression from refactoring**
The commit message explicitly states this "restores the original code
behavior" and includes a "Fix:" tag pointing to the commit that
introduced the regression. The original correct pattern was:
```c
if (vdev->config->enable_vq_after_reset(_vq))
return -EBUSY;
return err;
```
### 6. **Meets stable kernel criteria**
Per stable kernel rules, this fix:
- Fixes a real bug that affects users (incorrect error reporting)
- Is already in Linus' tree (merged by Paolo Abeni)
- Is small and easily reviewable
- Has been tested (Tested-by: Lei Yang)
- Has multiple maintainer acks (Jason Wang, Michael S. Tsirkin)
- Does not add new features or make risky changes
### 7. **Similar commits context**
While the similar commits shown are feature additions (introducing
virtqueue_resize functionality), this commit is fundamentally different
- it's a bug fix for error handling, not a feature addition.
The fix ensures that callers of `virtqueue_resize()` receive accurate
error information, which is critical for proper error handling and
recovery in virtio drivers that use queue resizing functionality.
drivers/virtio/virtio_ring.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c5f04234d9511..db4582687b958 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2739,7 +2739,7 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
void (*recycle)(struct virtqueue *vq, void *buf))
{
struct vring_virtqueue *vq = to_vvq(_vq);
- int err;
+ int err, err_reset;
if (num > vq->vq.num_max)
return -E2BIG;
@@ -2759,7 +2759,11 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num,
else
err = virtqueue_resize_split(_vq, num);
- return virtqueue_enable_after_reset(_vq);
+ err_reset = virtqueue_enable_after_reset(_vq);
+ if (err_reset)
+ return err_reset;
+
+ return err;
}
EXPORT_SYMBOL_GPL(virtqueue_resize);
--
2.39.5
