On Wed, Dec 08, 2010 at 12:16:56PM +1100, Dave Chinner wrote: > On Sat, Nov 27, 2010 at 08:56:03PM +1100, Nick Piggin wrote: > > This reverts commit 3825bdb7ed920845961f32f364454bee5f469abb. > > > > Patch is broken, you can't dget() without holding any locks! > > I believe you can - for the same reasons we can take a reference to > an inode without holding the inode_lock. That is, as long as the > caller already holds an active reference to the dentry, > dget() can be used to take another reference without needing the > dcache_lock. > > Such usage appears to be described in the comment above dget() and > there's a BUG_ON() in dget() to catch callers that don't already > have an active reference. An example of a valid unlocked dget(): > d_alloc() does an unlocked dget() to take a reference to the parent > dentry whichn we already are guaranteed to have a reference to. Of course you can dget if you already have a reference :) > As to d_validate() - it depends on the caller behaviour as to > whether the unlocked dget() is valid or not. From a cursory check > of the NCP and SMB readdir caches, both appear to hold an active > reference to the dentry it is passing to d_validate(). I don't see where? Can you point to where the refcount is taken? AFAIKS it drops the reference 3 lines after it puts the pointer into cache. > If that is > the case then there is nothing wrong with the way d_validate uses > dget(). Can someone with more SMB/NCP expertise than me validate the > use of cached dentries? Then why would it have to use d_validate if it has a reference? That is supposed to be for an "untrusted" pointer (which is why it had all the crazy checks that it's in kmem and in the right slab etc). -- 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
