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| Filename | Latest commit message | Latest commit date |
|---|---|---|
ec6ad9d99e
[ Upstream commit 1acfe2c1225899eab5ab724c91b7e1eb2881b9ab ]
In current packed virtqueue implementation, the avail_wrap_counter won't
flip, in the case when the driver supplies a descriptor chain with a
length equals to the queue size; total_sg == vq->packed.vring.num.
Let’s assume the following situation:
vq->packed.vring.num=4
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0
Then the driver adds a descriptor chain containing 4 descriptors.
We expect the following result with avail_wrap_counter flipped:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 1
But, the current implementation gives the following result:
vq->packed.next_avail_idx: 1
vq->packed.avail_wrap_counter: 0
To reproduce the bug, you can set a packed queue size as small as
possible, so that the driver is more likely to provide a descriptor
chain with a length equal to the packed queue size. For example, in
qemu run following commands:
sudo qemu-system-x86_64 \
-enable-kvm \
-nographic \
-kernel "path/to/kernel_image" \
-m 1G \
-drive file="path/to/rootfs",if=none,id=disk \
-device virtio-blk,drive=disk \
-drive file="path/to/disk_image",if=none,id=rwdisk \
-device virtio-blk,drive=rwdisk,packed=on,queue-size=4,\
indirect_desc=off \
-append "console=ttyS0 root=/dev/vda rw init=/bin/bash"
Inside the VM, create a directory and mount the rwdisk device on it. The
rwdisk will hang and mount operation will not complete.
This commit fixes the wrap counter error by flipping the
packed.avail_wrap_counter, when start of descriptor chain equals to the
end of descriptor chain (head == i).
Fixes:
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| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.