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    SubjectRe: [RFC 16/26] union-mount: Introduce union_mount structure
    On Mon, Jul 30, 2007 at 06:13:39PM +0200, Jan Blunck wrote:
    > +
    > +int append_to_union(struct vfsmount *mnt, struct dentry *dentry,
    > + struct vfsmount *dest_mnt, struct dentry *dest_dentry)
    > +{
    > + struct union_mount *this, *um;
    > +
    > + BUG_ON(!IS_MNT_UNION(mnt));
    > +
    > + this = union_alloc(dentry, mnt, dest_dentry, dest_mnt);
    > + if (!this)
    > + return -ENOMEM;
    > +
    > + spin_lock(&union_lock);
    > + um = union_lookup(dentry, mnt);
    > + if (um) {
    > + BUG_ON((um->u_next.dentry != dest_dentry) ||
    > + (um->u_next.mnt != dest_mnt));
    > + spin_unlock(&union_lock);
    > + union_put(this);
    > + return 0;
    > + }
    > + __union_hash(this);
    > + spin_unlock(&union_lock);
    > + return 0;
    > +}

    This breaks if we append to union stack from outside of the union.
    A particular case I hit is with a 3 layer union with a subdir union
    between topmost and bottom layer. Now if you create the same-named
    directory in the middle layer from outside of this union, you hit the
    above BUG_ON. The below patch fixes this and it applies on top of all of
    your patches.

    From: Bharata B Rao <bharata@linux.vnet.ibm.com>

    Direct additions to union stack from outside of the union is resulting in
    BUG_ON. But this is a valid case and hence needs to be supported. Modify
    append_to_union() to correctly handle this case.

    Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
    ---
    fs/namei.c | 8 +++++---
    fs/union.c | 32 ++++++++++++++++++++++++--------
    include/linux/union.h | 4 ++--
    3 files changed, 31 insertions(+), 13 deletions(-)

    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -512,7 +512,7 @@ static int __cache_lookup_union(struct n
    }

    /* now we know we found something "real" */
    - append_to_union(last.mnt, last.dentry, nd->mnt, dentry);
    + append_to_union(last.mnt, last.dentry, nd->mnt, dentry, 1);

    if (last.dentry != path->dentry)
    pathput(&last);
    @@ -789,7 +789,8 @@ static int __real_lookup_union(struct na
    }

    /* now we know we found something "real" */
    - append_to_union(last.mnt, last.dentry, next.mnt, next.dentry);
    + append_to_union(last.mnt, last.dentry,
    + next.mnt, next.dentry, 1);

    if (last.dentry != path->dentry)
    pathput(&last);
    @@ -1775,7 +1776,8 @@ static int __hash_lookup_union(struct na
    }

    /* now we know we found something "real" */
    - append_to_union(last.mnt, last.dentry, next.mnt, next.dentry);
    + append_to_union(last.mnt, last.dentry,
    + next.mnt, next.dentry, 1);

    if (last.dentry != path->dentry)
    pathput(&last);
    --- a/fs/union.c
    +++ b/fs/union.c
    @@ -248,7 +248,8 @@ int is_unionized(struct dentry *dentry,
    }

    int append_to_union(struct vfsmount *mnt, struct dentry *dentry,
    - struct vfsmount *dest_mnt, struct dentry *dest_dentry)
    + struct vfsmount *dest_mnt, struct dentry *dest_dentry,
    + int from_lookup)
    {
    struct union_mount *this, *um;

    @@ -264,11 +265,26 @@ int append_to_union(struct vfsmount *mnt
    spin_lock(&union_lock);
    um = union_lookup(dentry, mnt);
    if (um) {
    - BUG_ON((um->u_next.dentry != dest_dentry) ||
    - (um->u_next.mnt != dest_mnt));
    - spin_unlock(&union_lock);
    - union_put(this);
    - return 0;
    + if (um->u_next.dentry == dest_dentry &&
    + um->u_next.mnt == dest_mnt) {
    + spin_unlock(&union_lock);
    + union_put(this);
    + return 0;
    + }
    + if (from_lookup) {
    + __union_unhash(um);
    + list_del(&um->u_list);
    + list_del(&um->u_unions);
    + um->u_next.dentry->d_unionized--;
    + spin_unlock(&union_lock);
    + union_put(um);
    + spin_lock(&union_lock);
    + } else {
    + BUG();
    + spin_unlock(&union_lock);
    + union_put(this);
    + return 0;
    + }
    }
    list_add(&this->u_list, &mnt->mnt_unions);
    list_add(&this->u_unions, &dentry->d_unions);
    @@ -451,7 +467,7 @@ int attach_mnt_union(struct vfsmount *mn
    if (!IS_MNT_UNION(mnt))
    return 0;

    - return append_to_union(mnt, mnt->mnt_root, dest_mnt, dest_dentry);
    + return append_to_union(mnt, mnt->mnt_root, dest_mnt, dest_dentry, 0);
    }

    void detach_mnt_union(struct vfsmount *mnt)
    @@ -941,7 +957,7 @@ struct dentry *union_create_topmost(stru
    UM_DEBUG_DENTRY(dentry);

    res = append_to_union(nd->mnt, dentry, path->mnt,
    - path->dentry);
    + path->dentry, 0);
    if (res) {
    dput(dentry);
    dentry = ERR_PTR(res);
    --- a/include/linux/union.h
    +++ b/include/linux/union.h
    @@ -44,7 +44,7 @@ struct union_mount {

    extern int is_unionized(struct dentry *, struct vfsmount *);
    extern int append_to_union(struct vfsmount *, struct dentry *,
    - struct vfsmount *, struct dentry *);
    + struct vfsmount *, struct dentry *, int);
    extern int follow_union_down(struct vfsmount **, struct dentry **);
    extern int follow_union_mount(struct vfsmount **, struct dentry **);
    extern void __d_drop_unions(struct dentry *);
    @@ -65,7 +65,7 @@ extern int union_copyup(struct nameidata
    #define IS_UNION(x) (0)
    #define IS_MNT_UNION(x) (0)
    #define is_unionized(x, y) (0)
    -#define append_to_union(x1, y1, x2, y2) ({ BUG(); (0); })
    +#define append_to_union(x1, y1, x2, y2, z) ({ BUG(); (0); })
    #define follow_union_down(x, y) ({ (0); })
    #define follow_union_mount(x, y) ({ (0); })
    #define __d_drop_unions(x) do { } while (0)
    -
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      Last update: 2007-08-06 08:03    [W:0.028 / U:65.704 seconds]
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