commit 3b47ebe66a0994339888bc824926a1951eef8075
Author: Erez_Zadok <[EMAIL PROTECTED]>
Date: Fri Aug 31 11:24:06 2007 -0400
Unionfs: document lockdep issues
Signed-off-by: Erez Zadok <[EMAIL PROTECTED]>
diff --git a/Documentation/filesystems/unionfs/issues.txt
b/Documentation/filesystems/unionfs/issues.txt
index 6101ebf..c3a0aef 100644
--- a/Documentation/filesystems/unionfs/issues.txt
+++ b/Documentation/filesystems/unionfs/issues.txt
@@ -8,5 +8,17 @@ KNOWN Unionfs 2.1 ISSUES:
currently introducing VFS changes to fs/namei.c's do_path_lookup() to
allow proper file lookup and opening in stackable file systems.
+2. Lockdep (a debugging feature) isn't aware of stacking, and so it
+ incorrectly complains about locking problems. The problem boils down to
+ this: Lockdep considers all objects of a certain type to be in the same
+ class, for example, all inodes. Lockdep doesn't like to see a lock held
+ on two inodes within the same task, and warns that it could lead to a
+ deadlock. However, stackable file systems do precisely that: they lock
+ an upper object, and then a lower object, in a strict order to avoid
+ locking problems; in addition, Unionfs, as a fan-out file system, may
+ have to lock several lower inodes. We are currently looking into Lockdep
+ to see how to make it aware of stackable file systems. In the mean time,
+ if you get any warnings from Lockdep, you can safely ignore them (or feel
+ free to report them to the Unionfs maintainers, just to be sure).
For more information, see <http://unionfs.filesystems.org/>.
_______________________________________________
unionfs-cvs mailing list: http://unionfs.filesystems.org/
[email protected]
http://www.fsl.cs.sunysb.edu/mailman/listinfo/unionfs-cvs
