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Message-ID: <20070626125006.GG31489@sgi.com>
Date: Tue, 26 Jun 2007 22:50:06 +1000
From: David Chinner <dgc@....com>
To: Jarek Poplawski <jarkao2@...pl>
Cc: David Chinner <dgc@....com>, Ingo Molnar <mingo@...e.hu>,
Satyam Sharma <satyam.sharma@...il.com>,
Johannes Weiner <hannes-kernel@...urebad.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
xfs-masters@....sgi.com
Subject: Re: [BUG] Lockdep warning with XFS on 2.6.22-rc6
On Tue, Jun 26, 2007 at 11:35:20AM +0200, Jarek Poplawski wrote:
> On 26-06-2007 04:16, David Chinner wrote:
> > It does both - parent-first/child-second and ascending inode # order,
> > which is where the problem is. standing alone, these seem fine, but
> > they don't appear to work when the child has a lower inode number
> > than the parent.
> ...
>
> >From xfs_inode.h:
>
> /*
> * Flags for lockdep annotations.
> *
> * XFS_I[O]LOCK_PARENT - for operations that require locking two inodes
> * (ie directory operations that require locking a directory inode and
> * an entry inode). The first inode gets locked with this flag so it
> * gets a lockdep subclass of 1 and the second lock will have a lockdep
> * subclass of 0.
> *
> * XFS_I[O]LOCK_INUMORDER - for locking several inodes at the some time
> * with xfs_lock_inodes(). This flag is used as the starting subclass
> * and each subsequent lock acquired will increment the subclass by one.
> * So the first lock acquired will have a lockdep subclass of 2, the
> * second lock will have a lockdep subclass of 3, and so on.
> */
>
> I don't know xfs code, and probably miss something, but it seems
> there could be some inconsistency: lockdep warning shows mr_lock/1
> taken both before and after mr_lock (i.e. /0). According to the
> above comment there should be always 1 before 0...
That just fired some rusty neurons.
#define XFS_IOLOCK_SHIFT 16
#define XFS_IOLOCK_PARENT (1 << XFS_IOLOCK_SHIFT)
#define XFS_IOLOCK_INUMORDER (2 << XFS_IOLOCK_SHIFT)
#define XFS_ILOCK_SHIFT 24
#define XFS_ILOCK_PARENT (1 << XFS_ILOCK_SHIFT)
#define XFS_ILOCK_INUMORDER (2 << XFS_ILOCK_SHIFT)
So, in a lock_mode parameter, the upper 8 bits are for the ILOCK lockdep
subclass, and the 16..23 bits are for the IOLOCK lockdep subclass.
Where do we add them?
static inline int
xfs_lock_inumorder(int lock_mode, int subclass)
{
if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL))
lock_mode |= (subclass + XFS_IOLOCK_INUMORDER) << XFS_IOLOCK_SHIFT;
if (lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL))
lock_mode |= (subclass + XFS_ILOCK_INUMORDER) << XFS_ILOCK_SHIFT;
return lock_mode;
}
OH, look at those nice overflow bugs in that in that code. We shift
the XFS_IOLOCK_INUMORDER and XFS_ILOCK_INUMORDER bits out the far
side of the lock_mode variable result in lock subclasses of 0-3 instead
of 2-5....
Bugger, eh?
Patch below should fix this (untested).
Jarek - thanks for pointing what I should have seen earlier.
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
---
fs/xfs/xfs_inode.h | 15 +++++++++------
fs/xfs/xfs_vnodeops.c | 4 ++--
2 files changed, 11 insertions(+), 8 deletions(-)
Index: 2.6.x-xfs-new/fs/xfs/xfs_vnodeops.c
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/xfs_vnodeops.c 2007-06-25 13:56:20.000000000 +1000
+++ 2.6.x-xfs-new/fs/xfs/xfs_vnodeops.c 2007-06-26 22:46:55.412060598 +1000
@@ -2256,9 +2256,9 @@ static inline int
xfs_lock_inumorder(int lock_mode, int subclass)
{
if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL))
- lock_mode |= (subclass + XFS_IOLOCK_INUMORDER) << XFS_IOLOCK_SHIFT;
+ lock_mode |= (subclass + XFS_LOCK_INUMORDER) << XFS_IOLOCK_SHIFT;
if (lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL))
- lock_mode |= (subclass + XFS_ILOCK_INUMORDER) << XFS_ILOCK_SHIFT;
+ lock_mode |= (subclass + XFS_LOCK_INUMORDER) << XFS_ILOCK_SHIFT;
return lock_mode;
}
Index: 2.6.x-xfs-new/fs/xfs/xfs_inode.h
===================================================================
--- 2.6.x-xfs-new.orig/fs/xfs/xfs_inode.h 2007-06-20 17:59:35.000000000 +1000
+++ 2.6.x-xfs-new/fs/xfs/xfs_inode.h 2007-06-26 22:46:50.104749916 +1000
@@ -386,19 +386,22 @@ xfs_iflags_test(xfs_inode_t *ip, unsigne
* gets a lockdep subclass of 1 and the second lock will have a lockdep
* subclass of 0.
*
- * XFS_I[O]LOCK_INUMORDER - for locking several inodes at the some time
+ * XFS_LOCK_INUMORDER - for locking several inodes at the some time
* with xfs_lock_inodes(). This flag is used as the starting subclass
* and each subsequent lock acquired will increment the subclass by one.
* So the first lock acquired will have a lockdep subclass of 2, the
- * second lock will have a lockdep subclass of 3, and so on.
+ * second lock will have a lockdep subclass of 3, and so on. It is
+ * the responsibility of the class builder to shift this to the correct
+ * portion of the lock_mode lockdep mask.
*/
+#define XFS_LOCK_PARENT 1
+#define XFS_LOCK_INUMORDER 2
+
#define XFS_IOLOCK_SHIFT 16
-#define XFS_IOLOCK_PARENT (1 << XFS_IOLOCK_SHIFT)
-#define XFS_IOLOCK_INUMORDER (2 << XFS_IOLOCK_SHIFT)
+#define XFS_IOLOCK_PARENT (XFS_LOCK_PARENT << XFS_IOLOCK_SHIFT)
#define XFS_ILOCK_SHIFT 24
-#define XFS_ILOCK_PARENT (1 << XFS_ILOCK_SHIFT)
-#define XFS_ILOCK_INUMORDER (2 << XFS_ILOCK_SHIFT)
+#define XFS_ILOCK_PARENT (XFS_LOCK_PARENT << XFS_ILOCK_SHIFT)
#define XFS_IOLOCK_DEP_MASK 0x00ff0000
#define XFS_ILOCK_DEP_MASK 0xff000000
-
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