diff options
| author | Al Viro <viro@zeniv.linux.org.uk> | 2025-05-07 14:05:50 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2025-06-29 18:13:41 -0400 |
| commit | 49acacdc7cd3c1dcf5190a80ea9e6ca2ffa06cec (patch) | |
| tree | 26537c40831906ea8368f1addcafafd838e025f1 /fs/namespace.c | |
| parent | d08fa7f44ae7f5ad5c842e15f2412790736a6144 (diff) | |
clone_mnt(): simplify the propagation-related logics
The underlying rules are simple:
* MNT_SHARED should be set iff ->mnt_group_id of new mount ends up
non-zero.
* mounts should be on the same ->mnt_share cyclic list iff they have
the same non-zero ->mnt_group_id value.
* CL_PRIVATE is mutually exclusive with MNT_SHARED, MNT_SLAVE,
MNT_SHARED_TO_SLAVE and MNT_EXPIRE; the whole point of that thing is to
get a clone of old mount that would *not* be on any namespace-related
lists.
The above allows to make the logics more straightforward; what's more,
it makes the proof that invariants are maintained much simpler.
The variant in mainline is safe (aside of a very narrow race with
unsafe modification of mnt_flags right after we had the mount exposed
in superblock's ->s_mounts; theoretically it can race with ro remount
of the original, but it's not easy to hit), but proof of its correctness
is really unpleasant.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/namespace.c')
| -rw-r--r-- | fs/namespace.c | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index 791904128f1e..12cf69da4320 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1301,6 +1301,9 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, if (!mnt) return ERR_PTR(-ENOMEM); + mnt->mnt.mnt_flags = READ_ONCE(old->mnt.mnt_flags) & + ~MNT_INTERNAL_FLAGS; + if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE)) mnt->mnt_group_id = 0; /* not a peer of original */ else @@ -1312,8 +1315,8 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, goto out_free; } - mnt->mnt.mnt_flags = old->mnt.mnt_flags; - mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL|MNT_LOCKED); + if (mnt->mnt_group_id) + set_mnt_shared(mnt); atomic_inc(&sb->s_active); mnt->mnt.mnt_idmap = mnt_idmap_get(mnt_idmap(&old->mnt)); @@ -1326,22 +1329,20 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, list_add_tail(&mnt->mnt_instance, &sb->s_mounts); unlock_mount_hash(); + if (flag & CL_PRIVATE) // we are done with it + return mnt; + + if (peers(mnt, old)) + list_add(&mnt->mnt_share, &old->mnt_share); + if ((flag & CL_SLAVE) || ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) { list_add(&mnt->mnt_slave, &old->mnt_slave_list); mnt->mnt_master = old; - CLEAR_MNT_SHARED(mnt); - } else if (!(flag & CL_PRIVATE)) { - if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old)) - list_add(&mnt->mnt_share, &old->mnt_share); - if (IS_MNT_SLAVE(old)) - list_add(&mnt->mnt_slave, &old->mnt_slave); + } else if (IS_MNT_SLAVE(old)) { + list_add(&mnt->mnt_slave, &old->mnt_slave); mnt->mnt_master = old->mnt_master; - } else { - CLEAR_MNT_SHARED(mnt); } - if (flag & CL_MAKE_SHARED) - set_mnt_shared(mnt); /* stick the duplicate mount on the same expiry list * as the original if that was on one */ @@ -1349,7 +1350,6 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root, if (!list_empty(&old->mnt_expire)) list_add(&mnt->mnt_expire, &old->mnt_expire); } - return mnt; out_free: |