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

[Ian Whitfield]

On Wed, Apr 23, 2025 at 03:21:30PM -0700, Ian Whitfield 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
> 

Applied to jammy:linux-gke and noble:linux-gke master-next branches and
jammy:linux-gkeop and noble:linux-gkeop gkeop-next branches.