On May 20, 2011, at 10:17 AM, Miklos Szeredi wrote: > Miklos Szeredi <miklos@xxxxxxxxxx> writes: > >> Erez Zadok <ezk@xxxxxxxxxxxxxxxxx> writes: >> >>> I tried your overlayfs.v9 git repo w/ racer, using two separate ext3 >>> filesystems (one for lowerdir and another for upperdir). I got the >>> WARN_ON in ovl_permission to trigger within about 10 minutes of >>> testing. Looking at the code, I see a problem in returning w/o >>> cleaning up an dput-ing the alias dentry. Simple patch enclosed >>> below. >> >> Hmm, thanks. The more interesting question is: why does that WARN_ON >> trigger? I'll look into it. > > I think I found the cause of all the bug and oopsen you are seeing. > > Overlayfs expects upper and lower dentries to be always positive, it > never stores negative dentries there, there's no point, instead it > stores NULL. > > There are basically two ways a positive dentry can become negative: > > A) dentry becomes unhashed with d_count == 0 > > B) d_delete with d_count == 1 > > Case A is not possible in our case, since overlayfs keeps a ref on the > upper/lower dentries for the lifetime of the overlayfs dentry. > > Case B is however possible, since no extra ref is taken before calling > vfs_unlink/vfs_rmdir. So it looks like this is being triggered. > > This is easy to solve, just grab a ref to upperdentry before > unlink/rmdir. Equivalent is if we grab an extra reference from the > start. The below patch does this. > > With the patch I can't trigger the bugs anymore. > > Erez, could you please also check if reverting your patches and applying > this one fixes all the bugs? Done: reverted my ovl patches and applied yours. And indeed, the NULL oopses don't show up after 10 minutes of running. Just to be sure, I ran overlayfs on top of ext2, ext3, xfs, reiserfs, and tmps — no oopses. And I wasn't able to reproduce the WARN_ON in ovl_permission. Are you interested in testing overlayfs on top of NFS at this time? You need xattr support right? Stacking over NFS takes extra effort, esp. b/c of the pesky silly deleted files and needing a nameidata everywhere (but I managed after a while to get Wrapfs working stably over nfs3). > Thanks, > Miklos > > commit 9192816148e2c6b1d610226b1fc1c04c36216370 > Author: Miklos Szeredi <mszeredi@xxxxxxx> > Date: Fri May 20 16:07:34 2011 +0200 > > ovl: don't allow upperdentry to go negative [...] Do you commit such patches to a master branch, the v9 branch, or some other one; I'd like to be able to git pull Thanks, Erez. -- 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
