From: Laurent Vivier lvivier@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: xuanzhuo@linux.alibaba.com Signed-off-by: Laurent Vivier lvivier@redhat.com Acked-by: Jason Wang jasowang@redhat.com Link: https://patch.msgid.link/20250521092236.661410-2-lvivier@redhat.com Tested-by: Lei Yang leiyang@redhat.com Acked-by: Michael S. Tsirkin mst@redhat.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@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 b784aab668670..4397392bfef00 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -2797,7 +2797,7 @@ int virtqueue_resize(struct virtqueue *_vq, u32 num, void (*recycle_done)(struct virtqueue *vq)) { struct vring_virtqueue *vq = to_vvq(_vq); - int err; + int err, err_reset;
if (num > vq->vq.num_max) return -E2BIG; @@ -2819,7 +2819,11 @@ 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);