On Wed, 2011-01-12 at 12:41 +0800, Ian Kent wrote: > On Tue, 2011-01-11 at 20:06 -0800, Linus Torvalds wrote: > > On Tue, Jan 11, 2011 at 7:59 PM, Ian Kent <raven@xxxxxxxxxx> wrote: > > > > > > Isn't the parent i_mutex held during mkdir()? > > > > Yes, but a lookup that hits in the dentry cache won't actually take > > the parent mutex. > > > > So as far as I can tell, doing the "d_add()" before setting d_op can > > result in another CPU coming in and seeing the newly added dentry > > before d_op has actually been initialized. Exactly because it will do > > the dentry lookup without holding any mutex. > > > > Of course, it's a very small window, so it probably doesn't matter in practice. > > > > >> Looking at it quickly, I don't think that would matter for > > >> the case at hand. I.e., that might be safer but it doesn't > > >> address the fact that these fields are getting initialized > > >> multiple times. > > > > > > Yeah, a hangover from changes done over time. > > > Not setting the dentry op in ->lookup() should fix this. > > > > Alex, care to test just removing the d_set_d_op() call from autofs4_lookup()? > > > > (That code is a bit scary, though - it explicitly makes it a negative > > dentry with a d_instantiate(dentry, NULL), and then hides the inode > > information away separately. Scary scary) > > Yeah, but the expire to mount races with autofs are difficult to handle > and this approach has worked well under heavy stress testing. It's true > that this would almost certainly be bad for a file system that supported > a full range of functionality but that's not so for autofs. I think I have to partly take this back. With Nick's recent vfs-scale patches this may not be OK any more since the dcache_lock has gone away and, at first glance, it looks like the added autofs4_lock spin lock doesn't provide the needed protection. Ian -- 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
