-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Jeff Mahoney wrote: > Andrea Righi wrote: >> Jeff Mahoney wrote: >>> I have the patchset that I mentioned, but I'm not proposing it for 2.6.21. >>> It's much too invasive to be introduced in an -rc7, but it does include >>> locking changes that I believe avoid this bug. >>> >>> Vladimir was right in his analysis that sometimes get_xa_root() takes the >>> reference once and other times twice, but not for the right reasons. I save >>> a reference to the xattr dir to avoid a lookup later, but when there are >>> multiple >>> getxattrs or listxattrs as the first xattr operation on the file system, we >>> can end >>> up taking a second reference when we shouldn't. This is because those >>> operations >>> are protected by read locks and the ->xattr_root pointer isn't protected by >>> anything >>> else. A quick fix would be to just extend the protection of the priv root's >>> i_mutex >>> around the assignment, and test first. The right fix involves a complete >>> rework of >>> the locking, and I have code to do that, it's just too late to include it >>> in 2.6.21. >>> >>> I'd love to know what Andrea (and now Andi Kleen) are doing to hit this >>> now. There >>> haven't been any changes in this code in a while, and the >>> shrink_dcache_for_umount() >>> has been around since October. I'm unable to reproduce locally so far, so >>> if Andrea >>> or Andi could see if this fixes it for them, I'd appreciate it. >> Jeff, your patch doesn't resolve, but you hit the problem. Actually, I >> think the xattr_root pointer must be protected also in get_xa_root() >> using the same private root i_mutex. >> >> I've tested the following patch and it resolves in my case. What do you >> think about it? could it be a reasonable fix? > > Your patch fixes the problem. That'll teach me to spin a patch up while I'm > headed > out the door. I think a cleaner solution for now is just to refactor > get_xa_root, > __get_xa_root, and create_xa_root into one function to simplify the lookup > and the > locking. I think I'll add another step to my patch set that removes the > caching of > xattr_root entirely or creates in on mount, as the priv root is created. The > privroot > must be cached to avoid a deadlock on the fs-root directory's i_mutex, but > xattr_root > was cached as an optimzation. If we need to take privroot->i_mutex every > time, there's > no point in caching it since it will probably be in the dcache anyway. > > -Jeff >
Ignore this patch. I missed a spot. - -Jeff - -- Jeff Mahoney SUSE Labs -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iD8DBQFGKiEHLPWxlyuTD7IRApRTAJ0WeJzkH7julSus9iqx+LYoAAlFOwCfahu0 4qN7BR/monh7ZcQWZ7Vmz3Y= =UNNw -----END PGP SIGNATURE----- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
