Messages in this thread | | | Date | Sun, 8 Sep 2013 17:25:40 -0700 | Subject | Re: [PATCH v7 1/4] spinlock: A new lockref structure for lockless update of refcount | From | Linus Torvalds <> |
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On Sun, Sep 8, 2013 at 5:03 PM, Al Viro <viro@zeniv.linux.org.uk> wrote: > > Well... unlazy_walk() is always followed by terminate_walk() very shortly, > but there's a minor problem - terminate_walk() uses "are we in RCU > mode?" for two things: > a) do we need to do path_put() here? > b) do we need to unlock? > If you introduce the third case ("no need to do unlock and no need to > do path_put()"), we'd better decide how to check for that case...
Actually, I decided to take advantage of those two cases instead, and I have a patch that I think does the right thing. Basically, I start off unlazy_walk() with just doing that lockref_get_not_dead() on the parent dentry, and if that fails I just return an error in RCU mode (so terminate_walk() does what it always used to do, and we haven't done anything else to any refcounts).
Now, if the lockref_get_not_dead() succeeded, that means that we have a reference on the nd->path.dentry, and we can now just do "mntget(nd->path.mnt);". Ta-Daa! We now have everything done for the non-RCU case for terminate_walk().
So after that point, we clear LOOKUP_RCU, and make the rule be that any return (error or success) has to do unlock_rcu_walk(). And then all the other refcounts are easy, we can just "dput(dentry);" after that.
I haven't tested it yet, I was going to reboot into it just now. But I'm attaching the patch here. Maybe I missed some detail, but it all seems simpler.
Note that this patch requires the "lockref_get_not_dead()" cleanup at the top of my current -git.
Linus [unhandled content-type:application/octet-stream] | |