On Thu, Nov 18, 2010 at 12:59:13PM -0800, David Miller wrote: > From: David Miller <davem@xxxxxxxxxxxxx> > Date: Thu, 18 Nov 2010 12:51:23 -0800 (PST) > > > From: Nick Piggin <npiggin@xxxxxxxxx> > > Date: Wed, 17 Nov 2010 01:09:01 +1100 > > > >> d_validate has been broken for a long time. > >> > >> kmem_ptr_validate does not guarantee that a pointer can be dereferenced > >> if it can go away at any time. Even rcu_read_lock doesn't help, because > >> the pointer might be queued in RCU callbacks but not executed yet. > >> > >> So the parent cannot be checked, nor the name hashed. The dentry pointer > >> can not be touched until it can be verified under lock. Hashing simply > >> cannot be used. > >> > >> Instead, verify the parent/child relationship by traversing parent's > >> d_child list. It's slow, but only ncpfs and the destaged smbfs care > >> about it, at this point. > >> > >> Signed-off-by: Nick Piggin <npiggin@xxxxxxxxx> > > > > This won't apply because is conflicts with Christoph Hellwig's > > RCU conversion of d_validate(). > > > > Which is a change that went in more than a month ago. > > In fact the conflicts of your patch set are even more pervasive, since > all dcache hash traversals are essentially RCU protected instead of > dcache_lock protected right now. Not sure what you mean there. The patches are against upstream+revert of the last d_validate patch. dcache_lock splitup of this series is to split the lock out of all the other paths, and importantly allow d_lock to protect the complete dcache state of the dentry. Next 2 steps (that depend on this series but not on each other) are fine grained locking of the split locks, and rcu-walk. rcu-walk is what I called store-free path walking, because we extend RCU not only to the hash lookup but the entire path walk. I'll get all that out when I get a bit of time to work on it again. Thanks, Nick -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
