ACK: [SRU][J:linux-gke/J:linux-gkeop/N:linux-gke/N:linux-gkeop][PATCH 0/1] nfs: clear SB_RDONLY before getting superblock

[Benjamin Wheeler]

On Wed, Apr 23, 2025 at 6:22 PM Ian Whitfield <ian.whitfield at canonical.com>
wrote:

> BugLink: https://bugs.launchpad.net/bugs/2108862
>
> [Impact]
> Google: "We discovered an issue with upstream patch
> 52cb7f8f177878b4f22397b9c4d2c8f743766be3 that caused RW nfs mounts to be
> mounted
> as RO when there was an existing nfs RO mount on the same node."
>
> The break commit was found on jammy:gke/gkeop and noble:gke/gkeop.
>
> [Fix]
> Apply the fix proposed on lkml at
>
> https://lore.kernel.org/lkml/20250304130533.549840-1-lilingfeng3@huawei.com/T/
>
> The commit titled "nfs: clear SB_RDONLY before getting superblock" should
> address the issue. Because it has not been applied to any trees, it will be
> initially applied as an UBUNTU: SAUCE: patch.
>
> [Test]
> A reproducer was included with the initial bug report at
> https://www.spinics.net/lists/linux-nfs/msg109544.html
>
> # Reproducer
> mkdir -p /export/{stuff,things}/dir{1,2,3,4}
> echo '/export/stuff *(rw)' >> /etc/exports
> echo '/export/things *(rw)' >> /etc/exports
> systemctl restart nfs-server
>
> mount -t nfs -o ro,vers=3 localhost:/export/stuff /mnt/stuff
> mount -t nfs -o rw,vers=3 localhost:/export/things /mnt/things
> grep -w nfs /proc/mounts
> # note that both mountpoints are ro, despite the explicit ro/rw options
> # reversing the order of mounts gives a different result
>
> I've confirmed that the bug is reproduced on noble:linux-gke and
> jammy:linux-gke
> and that the patched versions of the kernel do not reproduce the issue.
> After
> the fix, the read only mount is properly tagged as read only, and the
> read/write
> mount is properly tagged as read/write.
>
> [Where problems could occur]
> This is a fairly small patch which directly addresses a reproducible issue,
> so its scope of influence should be pretty limited. We do take some risk by
> applying this patch before it has been approved by upstream maintainers,
> so this
> won't be going into generic kernels until then.
>
> Li Lingfeng (1):
>   UBUNTU: SAUCE: nfs: clear SB_RDONLY before getting superblock
>
>  fs/nfs/super.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> --
> 2.43.0
>
>
> --
> kernel-team mailing list
> kernel-team at lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
>

Acked-by: Benjamin Wheeler <benjamin.wheeler at canonical.com>
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