5.15-stable review patch. If anyone has any objections, please let me know.
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From: Li Lingfeng lilingfeng3@huawei.com
[ Upstream commit 52cb7f8f177878b4f22397b9c4d2c8f743766be3 ]
When exporting only one file system with fsid=0 on the server side, the client alternately uses the ro/rw mount options to perform the mount operation, and a new vfsmount is generated each time.
It can be reproduced as follows: [root@localhost ~]# mount /dev/sda /mnt2 [root@localhost ~]# echo "/mnt2 *(rw,no_root_squash,fsid=0)" >/etc/exports [root@localhost ~]# systemctl restart nfs-server [root@localhost ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/ /mnt/sdaa [root@localhost ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/ /mnt/sdaa [root@localhost ~]# mount -t nfs -o ro,vers=4 127.0.0.1:/ /mnt/sdaa [root@localhost ~]# mount -t nfs -o rw,vers=4 127.0.0.1:/ /mnt/sdaa [root@localhost ~]# mount | grep nfs4 127.0.0.1:/ on /mnt/sdaa type nfs4 (ro,relatime,vers=4.2,rsize=1048576,... 127.0.0.1:/ on /mnt/sdaa type nfs4 (rw,relatime,vers=4.2,rsize=1048576,... 127.0.0.1:/ on /mnt/sdaa type nfs4 (ro,relatime,vers=4.2,rsize=1048576,... 127.0.0.1:/ on /mnt/sdaa type nfs4 (rw,relatime,vers=4.2,rsize=1048576,... [root@localhost ~]#
We expected that after mounting with the ro option, using the rw option to mount again would return EBUSY, but the actual situation was not the case.
As shown above, when mounting for the first time, a superblock with the ro flag will be generated, and at the same time, in do_new_mount_fc --> do_add_mount, it detects that the superblock corresponding to the current target directory is inconsistent with the currently generated one (path->mnt->mnt_sb != newmnt->mnt.mnt_sb), and a new vfsmount will be generated.
When mounting with the rw option for the second time, since no matching superblock can be found in the fs_supers list, a new superblock with the rw flag will be generated again. The superblock in use (ro) is different from the newly generated superblock (rw), and a new vfsmount will be generated again.
When mounting with the ro option for the third time, the superblock (ro) is found in fs_supers, the superblock in use (rw) is different from the found superblock (ro), and a new vfsmount will be generated again.
We can switch between ro/rw through remount, and only one superblock needs to be generated, thus avoiding the problem of repeated generation of vfsmount caused by switching superblocks.
Furthermore, This can also resolve the issue described in the link.
Fixes: 275a5d24bf56 ("NFS: Error when mounting the same filesystem with different options") Link: https://lore.kernel.org/all/20240604112636.236517-3-lilingfeng@huaweicloud.c... Signed-off-by: Li Lingfeng lilingfeng3@huawei.com Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/nfs/internal.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/nfs/internal.h b/fs/nfs/internal.h index f82264fcbb07e..692018327b5ff 100644 --- a/fs/nfs/internal.h +++ b/fs/nfs/internal.h @@ -11,7 +11,7 @@ #include <linux/nfs_page.h> #include <linux/wait_bit.h>
-#define NFS_SB_MASK (SB_RDONLY|SB_NOSUID|SB_NODEV|SB_NOEXEC|SB_SYNCHRONOUS) +#define NFS_SB_MASK (SB_NOSUID|SB_NODEV|SB_NOEXEC|SB_SYNCHRONOUS)
extern const struct export_operations nfs_export_ops;