lkml.org 
[lkml]   [2019]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [GIT PULL] Ceph fixes for 5.1-rc7
    From
    Date
    On Thu, 2019-04-25 at 21:09 +0100, Al Viro wrote:
    > On Thu, Apr 25, 2019 at 02:23:59PM -0400, Jeff Layton wrote:
    >
    > > I took a quick look at the dcache code to see if we had something like
    > > that before I did this, but I guess I didn't look closely enough. Those
    > > routines do look nicer than my hand-rolled version.
    > >
    > > I'll look at spinning up a patch to switch that over in the near future.
    >
    > Jeff asked to put the name length in there; looking at the existing users,
    > it does make sense. I propose turning struct name_snapshot into
    >
    > struct name_snapshot {
    > struct qstr name;
    > unsigned char inline_name[DNAME_INLINE_LEN];
    > };
    >
    > with
    > void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
    > {
    > spin_lock(&dentry->d_lock);
    > name->name = dentry->d_name;
    > if (unlikely(dname_external(dentry))) {
    > struct external_name *p = external_name(dentry);
    > atomic_inc(&p->u.count);
    > } else {
    > memcpy(name->inline_name, dentry->d_iname,
    > dentry->d_name.len + 1);
    > name->name.name = name->inline_name;
    > }
    > spin_unlock(&dentry->d_lock);
    > }
    >
    > and callers adjusted, initially simply by turning snapshot.name into
    > snapshot.name.name. Next step: overlayfs call site becoming
    > take_dentry_name_snapshot(&name, real);
    > this = lookup_one_len(name.name.name, connected, name.name.len);
    > Next: snotify stuff switched to passing struct qstr * - fsnotify_move()
    > first, then fsnotify(). That one would
    > * leave callers passing NULL alone
    > * have the callers passing snapshot.name.name pass &snapshot.name
    > * fsnotify_dirent() pass the entire &dentry->d_name, not just
    > dentry->d_name.name (that's dependent upon parent being held exclusive;
    > devpts plays fast and loose here, relying upon the lack of any kind of
    > renames, explicit or implicit, in that fs)
    > * ditto for remaining call in fsnotify_move() (both parents
    > are locked in all callers, thankfully)
    > * ditto for fsnotify_link()
    > * kernfs callers in kernfs_notify_workfn() would grow strlen().
    > Next: send_to_group() and ->handle_event() instances switched to passing
    > struct qstr *.
    > Next: inotify_handle_event() doesn't need to bother with strlen().
    > Next: audit_update_watch() and audit_compare_dname_path() switched to
    > struct qstr *. Callers in __audit_inode_child() pass the entire
    > &dentry->d_name. strlen() inside audit_compare_dname_path() goes away.
    >
    > Objections?

    I have some patches that do what you lay out above. They build but I
    haven't ran them through much testing yet.

    It turns out though that using name_snapshot from ceph is a bit more
    tricky. In some cases, we have to call ceph_mdsc_build_path to build up
    a full path string. We can't easily populate a name_snapshot from there
    because struct external_name is only defined in fs/dcache.c.

    I could add some routines to do this, but it feels a lot like I'm
    abusing internal dcache interfaces. I'll keep thinking about it though.

    While we're on the subject though:

    struct external_name {
    union {
    atomic_t count;
    struct rcu_head head;
    } u;
    unsigned char name[];
    };

    Is it really ok to union the count and rcu_head there?

    I haven't trawled through all of the code yet, but what prevents someone
    from trying to access the count inside an RCU critical section, after
    call_rcu has been called on it?

    Thanks,
    --
    Jeff Layton <jlayton@kernel.org>

    \
     
     \ /
      Last update: 2019-04-26 18:25    [W:2.377 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site