On Mon 18-06-12 17:19:30, J. Bruce Fields wrote: > On Wed, May 30, 2012 at 10:12:57PM +0200, Jan Kara wrote: > > On Wed 30-05-12 13:37:09, J. Bruce Fields wrote: > > > On Tue, May 29, 2012 at 10:08:56PM +0200, Jan Kara wrote: > > > > On Tue 29-05-12 21:50:19, Jan Kara wrote: > > > > > On Mon 28-05-12 17:05:11, Ted Tso wrote: > > > > > > On Mon, May 28, 2012 at 02:29:05PM -0600, Andreas Dilger wrote: > > > > > > > This patch is good from the POV of covering all filesystems, and > > > > > > > avoiding the deadlock at the dcache level. It would be possible to > > > > > > > detect this problem in the filesystem itself during lookup, before > > > > > > > the bad link got into the dcache itself. Something like: > > > > > > > > > > > > I like that as a solution for detecting the problem in ext4. As you > > > > > > say, it's still an issue for other file systems, and so the patch I > > > > > > proposed is still probably a good idea for the VFS. But this way ext4 > > > > > > (and ext3 when Jan backports it) will be able to detect the problem > > > > > > and mark the file system as being corrupted. > > > > > Actually, I think there's even better way. d_splice_alias() can rather > > > > > easily detect the problem and report it to filesystem. The advantage is > > > > > that the check in d_splice_alias() can catch any "hardlinks" to > > > > > directories, not just self loops. The patch is attached, I also have > > > > > corresponding handling written for ext? filesystems but that's trivial. > > > > > I'll post the whole series to Al to have a look. > > > > And now with the attachment. Sorry. > > > > > > Well, my understanding of d_splice_alias is that it should just return > > > the existing dentry instead of failing. (It does that now for > > > DISCONNECTED dentries, but I don't understand why they're special.) > > > So that's what: > > > > > > http://git.kernel.org/?p=linux/kernel/git/viro/vfs.git;a=commit;h=9d345b3217b384813680901d42eae3fb380b9f77 > > > > > > does. > > Thanks for the pointer. In the case I tried to solve, returning the > > existing dentry will solve the deadlocks, just user won't be warned that > > the filesystem is corrupted. Since you seem to describe a valid case where > > we can spot other !DISCONNECTED dentry of a directory, I guess we have no > > other choice than using your approach. > > But my patch got reverted, on suspicion that it was either wrong or > covering up some other problem: > > http://marc.info/?l=linux-fsdevel&m=133917767003505&w=2 > > ... which an approach like yours might help at least find? So maybe > it's worth another try. Yeah, I'll rebase and resubmit those patches (plus fixup error handling as Al suggested) today or tomorrow. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
