| Message ID | 20240604112636.236517-3-lilingfeng@huaweicloud.com |
|---|---|
| State | New |
| Headers | show |
| Series | NFSv4: set sb_flags to second superblock | expand |
I think this may be a problem, but I'm unable to come up with a suitable solution. Would you mind providing some suggestions? 在 2024/6/4 19:26, Li Lingfeng 写道: > From: Li Lingfeng <lilingfeng3@huawei.com> > > During the process of mounting an NFSv4 client, two superblocks will be > created in sequence. The first superblock corresponds to the root > directory exported by the server, and the second superblock corresponds to > the directory that will be actually mounted. The first superblock will > eventually be destroyed. > The flag passed from user mode will only be passed to the first > superblock, resulting in the actual used superblock not carrying the flag > passed from user mode(fs_context_for_submount() will set sb_flags as 0). > > If the 'ro' parameter is used in two consecutive mount commands, only the > first execution will create a new vfsmount, and the kernel will return > EBUSY on the second execution. However, if a remount command with the 'ro' > parameter is executed between the two mount commands, both mount commands > will create new vfsmounts. > > The superblock generated after the first mount command does not have the > 'ro' flag, and the read-only status of the file system is implemented by > checking the read-only flag of the vfsmount. After executing the remount > command, the 'ro' flag will be added to the superblock. When the second > mount command is executed, the comparison result between the superblock > with the 'ro' flag and the fs_context without the flag in the > nfs_compare_mount_options() function will be different, resulting in the > creation of a new vfsmount. > > This problem can be reproduced by performing the following operations: > mount -t nfs -o ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb > mount -t nfs -o remount,ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb > mount -t nfs -o ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb > Two vfsmounts are generated: > [root@localhost ~]# mount | grep nfs > 192.168.240.250:/sdb on /mnt/sdb type nfs4 (ro,relatime,vers=4.0, > rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2, > sec=sys,clientaddr=192.168.240.251,local_lock=none,addr=192.168.240.250) > 192.168.240.250:/sdb on /mnt/sdb type nfs4 (ro,relatime,vers=4.0, > rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2, > sec=sys,clientaddr=192.168.240.251,local_lock=none,addr=192.168.240.250) > > Fix this by setting sb_flags to second superblock. > > Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com> > --- > fs/nfs/namespace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c > index 887aeacedebd..8b3d75af60d4 100644 > --- a/fs/nfs/namespace.c > +++ b/fs/nfs/namespace.c > @@ -158,7 +158,7 @@ struct vfsmount *nfs_d_automount(struct path *path, unsigned int sb_flags) > /* Open a new filesystem context, transferring parameters from the > * parent superblock, including the network namespace. > */ > - fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry, 0); > + fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry, sb_flags); > if (IS_ERR(fc)) > return ERR_CAST(fc); >
Friendly ping ... Thanks 在 2024/6/14 11:14, Li Lingfeng 写道: > I think this may be a problem, but I'm unable to come up with a > suitable solution. Would you mind providing some suggestions? > > 在 2024/6/4 19:26, Li Lingfeng 写道: >> From: Li Lingfeng <lilingfeng3@huawei.com> >> >> During the process of mounting an NFSv4 client, two superblocks will be >> created in sequence. The first superblock corresponds to the root >> directory exported by the server, and the second superblock >> corresponds to >> the directory that will be actually mounted. The first superblock will >> eventually be destroyed. >> The flag passed from user mode will only be passed to the first >> superblock, resulting in the actual used superblock not carrying the >> flag >> passed from user mode(fs_context_for_submount() will set sb_flags as 0). >> >> If the 'ro' parameter is used in two consecutive mount commands, only >> the >> first execution will create a new vfsmount, and the kernel will return >> EBUSY on the second execution. However, if a remount command with the >> 'ro' >> parameter is executed between the two mount commands, both mount >> commands >> will create new vfsmounts. >> >> The superblock generated after the first mount command does not have the >> 'ro' flag, and the read-only status of the file system is implemented by >> checking the read-only flag of the vfsmount. After executing the remount >> command, the 'ro' flag will be added to the superblock. When the second >> mount command is executed, the comparison result between the superblock >> with the 'ro' flag and the fs_context without the flag in the >> nfs_compare_mount_options() function will be different, resulting in the >> creation of a new vfsmount. >> >> This problem can be reproduced by performing the following operations: >> mount -t nfs -o ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb >> mount -t nfs -o remount,ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb >> mount -t nfs -o ro,vers=4.0 192.168.240.250:/sdb /mnt/sdb >> Two vfsmounts are generated: >> [root@localhost ~]# mount | grep nfs >> 192.168.240.250:/sdb on /mnt/sdb type nfs4 (ro,relatime,vers=4.0, >> rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2, >> >> sec=sys,clientaddr=192.168.240.251,local_lock=none,addr=192.168.240.250) >> 192.168.240.250:/sdb on /mnt/sdb type nfs4 (ro,relatime,vers=4.0, >> rsize=1048576,wsize=1048576,namlen=255,hard,proto=tcp,timeo=600,retrans=2, >> >> sec=sys,clientaddr=192.168.240.251,local_lock=none,addr=192.168.240.250) >> >> Fix this by setting sb_flags to second superblock. >> >> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com> >> --- >> fs/nfs/namespace.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c >> index 887aeacedebd..8b3d75af60d4 100644 >> --- a/fs/nfs/namespace.c >> +++ b/fs/nfs/namespace.c >> @@ -158,7 +158,7 @@ struct vfsmount *nfs_d_automount(struct path >> *path, unsigned int sb_flags) >> /* Open a new filesystem context, transferring parameters from the >> * parent superblock, including the network namespace. >> */ >> - fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, >> path->dentry, 0); >> + fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, >> path->dentry, sb_flags); >> if (IS_ERR(fc)) >> return ERR_CAST(fc);
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c index 887aeacedebd..8b3d75af60d4 100644 --- a/fs/nfs/namespace.c +++ b/fs/nfs/namespace.c @@ -158,7 +158,7 @@ struct vfsmount *nfs_d_automount(struct path *path, unsigned int sb_flags) /* Open a new filesystem context, transferring parameters from the * parent superblock, including the network namespace. */ - fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry, 0); + fc = fs_context_for_submount(path->mnt->mnt_sb->s_type, path->dentry, sb_flags); if (IS_ERR(fc)) return ERR_CAST(fc);