BTW - I tested applying both patches and the second one did fix the issue reported in https://lore.kernel.org/all/12d7ea53-1202-4e21-a7ef-431c94758ce5@xxxxxxxxxxxxxxxx/T/ On Tue, Mar 4, 2025 at 7:48 AM Li Lingfeng <lilingfeng3@xxxxxxxxxx> wrote: > > As described in the link, commit 52cb7f8f1778 ("nfs: ignore SB_RDONLY when > mounting nfs") removed the check for the ro flag when determining whether > to share the superblock, which caused issues when mounting different > subdirectories under the same export directory via NFSv3. However, this > change did not affect NFSv4. > > For NFSv3: > 1) A single superblock is created for the initial mount. > 2) When mounted read-only, this superblock carries the SB_RDONLY flag. > 3) Before commit 52cb7f8f1778 ("nfs: ignore SB_RDONLY when mounting nfs"): > Subsequent rw mounts would not share the existing ro superblock due to > flag mismatch, creating a new superblock without SB_RDONLY. > After the commit: > The SB_RDONLY flag is ignored during superblock comparison, and this leads > to sharing the existing superblock even for rw mounts. > Ultimately results in write operations being rejected at the VFS layer. > > For NFSv4: > 1) Multiple superblocks are created and the last one will be kept. > 2) The actually used superblock for ro mounts doesn't carry SB_RDONLY flag. > Therefore, commit 52cb7f8f1778 doesn't affect NFSv4 mounts. > > Clear SB_RDONLY before getting superblock when NFS_MOUNT_UNSHARED is not > set to fix it. > > Fixes: 52cb7f8f1778 ("nfs: ignore SB_RDONLY when mounting nfs") > Closes: https://lore.kernel.org/all/12d7ea53-1202-4e21-a7ef-431c94758ce5@xxxxxxxxxxxxxxxx/T/ > Signed-off-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx> > --- > fs/nfs/super.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/fs/nfs/super.c b/fs/nfs/super.c > index aeb715b4a690..3e5528c2c822 100644 > --- a/fs/nfs/super.c > +++ b/fs/nfs/super.c > @@ -1304,8 +1304,17 @@ int nfs_get_tree_common(struct fs_context *fc) > if (IS_ERR(server)) > return PTR_ERR(server); > > + /* > + * When NFS_MOUNT_UNSHARED is not set, NFS forces the sharing of a > + * superblock among each filesystem that mounts sub-directories > + * belonging to a single exported root path. > + * To prevent interference between different filesystems, the > + * SB_RDONLY flag should be removed from the superblock. > + */ > if (server->flags & NFS_MOUNT_UNSHARED) > compare_super = NULL; > + else > + fc->sb_flags &= ~SB_RDONLY; > > /* -o noac implies -o sync */ > if (server->flags & NFS_MOUNT_NOAC) > -- > 2.31.1 >
