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    SubjectRe: [PATCH 3/3] sysfs: Remove SYSFS_FLAG_REMOVED and use sd->s_nlink == 0 instead.
    Is this safe?

    What's the serialization with sysfs_link_sibling(), which you just made do

    sd->s_nlink++;
    if (!sd->s_nlink)
    sd->s_nlink = 1;

    in your previous patch?

    Yes, sysfs_link_sibling() runs under sysfs_mutex, but
    sysfs_dentry_delete() does not.

    So what protects sysfs_dentry_delete() from never seeing that bogus 0
    due to the overflow?

    Linus

    On Thu, Mar 8, 2012 at 1:37 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
    >
    > Now that we have a nlink field in sysfs_dirent report deleted
    > files and directories the traditional way with nlink == 0.
    >
    > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    > ---
    >  fs/sysfs/dir.c   |   11 +++++------
    >  fs/sysfs/sysfs.h |    1 -
    >  2 files changed, 5 insertions(+), 7 deletions(-)
    >
    > diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
    > index 1526567..b5471d1 100644
    > --- a/fs/sysfs/dir.c
    > +++ b/fs/sysfs/dir.c
    > @@ -202,7 +202,7 @@ static void sysfs_deactivate(struct sysfs_dirent *sd)
    >        DECLARE_COMPLETION_ONSTACK(wait);
    >        int v;
    >
    > -       BUG_ON(!(sd->s_flags & SYSFS_FLAG_REMOVED));
    > +       BUG_ON(sd->s_nlink != 0);
    >
    >        if (!(sysfs_type(sd) & SYSFS_ACTIVE_REF))
    >                return;
    > @@ -279,7 +279,7 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
    >  static int sysfs_dentry_delete(const struct dentry *dentry)
    >  {
    >        struct sysfs_dirent *sd = dentry->d_fsdata;
    > -       return !!(sd->s_flags & SYSFS_FLAG_REMOVED);
    > +       return sd->s_nlink == 0;
    >  }
    >
    >  static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
    > @@ -294,7 +294,7 @@ static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
    >        mutex_lock(&sysfs_mutex);
    >
    >        /* The sysfs dirent has been deleted */
    > -       if (sd->s_flags & SYSFS_FLAG_REMOVED)
    > +       if (sd->s_nlink == 0)
    >                goto out_bad;
    >
    >        /* The sysfs dirent has been moved? */
    > @@ -534,7 +534,7 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
    >  {
    >        struct sysfs_inode_attrs *ps_iattr;
    >
    > -       BUG_ON(sd->s_flags & SYSFS_FLAG_REMOVED);
    > +       BUG_ON(sd->s_nlink == 0);
    >
    >        sysfs_unlink_sibling(sd);
    >
    > @@ -546,7 +546,6 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
    >        }
    >
    >        sd->s_nlink = 0;
    > -       sd->s_flags |= SYSFS_FLAG_REMOVED;
    >        sd->u.removed_list = acxt->removed;
    >        acxt->removed = sd;
    >  }
    > @@ -946,7 +945,7 @@ static struct sysfs_dirent *sysfs_dir_pos(const void *ns,
    >        struct sysfs_dirent *parent_sd, loff_t hash, struct sysfs_dirent *pos)
    >  {
    >        if (pos) {
    > -               int valid = !(pos->s_flags & SYSFS_FLAG_REMOVED) &&
    > +               int valid = (pos->s_nlink > 0) &&
    >                        pos->s_parent == parent_sd &&
    >                        hash == pos->s_hash;
    >                sysfs_put(pos);
    > diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
    > index 71f9bf7..db2c5c5 100644
    > --- a/fs/sysfs/sysfs.h
    > +++ b/fs/sysfs/sysfs.h
    > @@ -98,7 +98,6 @@ struct sysfs_dirent {
    >  #define SYSFS_NS_TYPE_SHIFT            4
    >
    >  #define SYSFS_FLAG_MASK                        ~(SYSFS_NS_TYPE_MASK|SYSFS_TYPE_MASK)
    > -#define SYSFS_FLAG_REMOVED             0x080
    >
    >  static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
    >  {
    > --
    > 1.7.2.5
    >
    --
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