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    Subject[PATCH v3 093/110] namei: don't mangle nd->seq in lookup_fast()
    Date
    From: Al Viro <viro@zeniv.linux.org.uk>

    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    ---
    fs/namei.c | 38 +++++++++++++++++++++++---------------
    1 file changed, 23 insertions(+), 15 deletions(-)

    diff --git a/fs/namei.c b/fs/namei.c
    index 97315df..e321450 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -1134,7 +1134,7 @@ static inline int managed_dentry_rcu(struct dentry *dentry)
    * we meet a managed dentry that would need blocking.
    */
    static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
    - struct inode **inode)
    + struct inode **inode, unsigned *seqp)
    {
    for (;;) {
    struct mount *mounted;
    @@ -1161,7 +1161,7 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
    path->mnt = &mounted->mnt;
    path->dentry = mounted->mnt.mnt_root;
    nd->flags |= LOOKUP_JUMPED;
    - nd->seq = read_seqcount_begin(&path->dentry->d_seq);
    + *seqp = read_seqcount_begin(&path->dentry->d_seq);
    /*
    * Update the inode too. We don't need to re-check the
    * dentry sequence number here after this d_inode read,
    @@ -1397,7 +1397,8 @@ static struct dentry *__lookup_hash(struct qstr *name,
    * It _is_ time-critical.
    */
    static int lookup_fast(struct nameidata *nd,
    - struct path *path, struct inode **inode)
    + struct path *path, struct inode **inode,
    + unsigned *seqp)
    {
    struct vfsmount *mnt = nd->path.mnt;
    struct dentry *dentry, *parent = nd->path.dentry;
    @@ -1437,8 +1438,8 @@ static int lookup_fast(struct nameidata *nd,
    */
    if (__read_seqcount_retry(&parent->d_seq, nd->seq))
    return -ECHILD;
    - nd->seq = seq;

    + *seqp = seq;
    if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) {
    status = d_revalidate(dentry, nd->flags);
    if (unlikely(status <= 0)) {
    @@ -1449,10 +1450,10 @@ static int lookup_fast(struct nameidata *nd,
    }
    path->mnt = mnt;
    path->dentry = dentry;
    - if (likely(__follow_mount_rcu(nd, path, inode)))
    + if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
    return 0;
    unlazy:
    - if (unlazy_walk(nd, dentry, nd->seq))
    + if (unlazy_walk(nd, dentry, seq))
    return -ECHILD;
    } else {
    dentry = __d_lookup(parent, &nd->last);
    @@ -1543,7 +1544,7 @@ static void terminate_walk(struct nameidata *nd)
    put_link(nd);
    }

    -static int pick_link(struct nameidata *nd, struct path *link)
    +static int pick_link(struct nameidata *nd, struct path *link, unsigned seq)
    {
    int error;
    struct saved *last;
    @@ -1553,7 +1554,7 @@ static int pick_link(struct nameidata *nd, struct path *link)
    }
    if (nd->flags & LOOKUP_RCU) {
    if (unlikely(nd->path.mnt != link->mnt ||
    - unlazy_walk(nd, link->dentry, nd->seq))) {
    + unlazy_walk(nd, link->dentry, seq))) {
    return -ECHILD;
    }
    }
    @@ -1577,13 +1578,14 @@ static int pick_link(struct nameidata *nd, struct path *link)
    * so we keep a cache of "no, this doesn't need follow_link"
    * for the common case.
    */
    -static inline int should_follow_link(struct nameidata *nd, struct path *link, int follow)
    +static inline int should_follow_link(struct nameidata *nd, struct path *link,
    + int follow, unsigned seq)
    {
    if (likely(!d_is_symlink(link->dentry)))
    return 0;
    if (!follow)
    return 0;
    - return pick_link(nd, link);
    + return pick_link(nd, link, seq);
    }

    enum {WALK_GET = 1, WALK_PUT = 2};
    @@ -1592,6 +1594,7 @@ static int walk_component(struct nameidata *nd, int flags)
    {
    struct path path;
    struct inode *inode;
    + unsigned seq;
    int err;
    /*
    * "." and ".." are special - ".." especially so because it has
    @@ -1604,7 +1607,7 @@ static int walk_component(struct nameidata *nd, int flags)
    put_link(nd);
    return err;
    }
    - err = lookup_fast(nd, &path, &inode);
    + err = lookup_fast(nd, &path, &inode, &seq);
    if (unlikely(err)) {
    if (err < 0)
    return err;
    @@ -1614,6 +1617,7 @@ static int walk_component(struct nameidata *nd, int flags)
    return err;

    inode = path.dentry->d_inode;
    + seq = 0; /* we are already out of RCU mode */
    err = -ENOENT;
    if (d_is_negative(path.dentry))
    goto out_path_put;
    @@ -1621,11 +1625,12 @@ static int walk_component(struct nameidata *nd, int flags)

    if (flags & WALK_PUT)
    put_link(nd);
    - err = should_follow_link(nd, &path, flags & WALK_GET);
    + err = should_follow_link(nd, &path, flags & WALK_GET, seq);
    if (unlikely(err))
    return err;
    path_to_nameidata(&path, nd);
    nd->inode = inode;
    + nd->seq = seq;
    return 0;

    out_path_put:
    @@ -2342,7 +2347,7 @@ done:
    put_link(nd);
    path->dentry = dentry;
    path->mnt = nd->path.mnt;
    - error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW);
    + error = should_follow_link(nd, path, nd->flags & LOOKUP_FOLLOW, 0);
    if (unlikely(error))
    return error;
    mntget(path->mnt);
    @@ -2939,6 +2944,7 @@ static int do_last(struct nameidata *nd,
    bool will_truncate = (open_flag & O_TRUNC) != 0;
    bool got_write = false;
    int acc_mode = op->acc_mode;
    + unsigned seq;
    struct inode *inode;
    struct path save_parent = { .dentry = NULL, .mnt = NULL };
    struct path path;
    @@ -2959,7 +2965,7 @@ static int do_last(struct nameidata *nd,
    if (nd->last.name[nd->last.len])
    nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
    /* we _can_ be in RCU mode here */
    - error = lookup_fast(nd, &path, &inode);
    + error = lookup_fast(nd, &path, &inode, &seq);
    if (likely(!error))
    goto finish_lookup;

    @@ -3047,6 +3053,7 @@ retry_lookup:

    BUG_ON(nd->flags & LOOKUP_RCU);
    inode = path.dentry->d_inode;
    + seq = 0; /* out of RCU mode, so the value doesn't matter */
    if (unlikely(d_is_negative(path.dentry))) {
    path_to_nameidata(&path, nd);
    return -ENOENT;
    @@ -3054,7 +3061,7 @@ retry_lookup:
    finish_lookup:
    if (nd->depth)
    put_link(nd);
    - error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW);
    + error = should_follow_link(nd, &path, nd->flags & LOOKUP_FOLLOW, seq);
    if (unlikely(error))
    return error;

    @@ -3072,6 +3079,7 @@ finish_lookup:

    }
    nd->inode = inode;
    + nd->seq = seq;
    /* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */
    finish_open:
    error = complete_walk(nd);
    --
    2.1.4


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