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[PATCH 2/3] xfs: fix directory inode iolock lockdep false positive

To: xfs@xxxxxxxxxxx
Subject: [PATCH 2/3] xfs: fix directory inode iolock lockdep false positive
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 19 Feb 2014 15:16:41 +1100
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1392783402-4726-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1392783402-4726-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

The change to add the IO lock to protect the directory extent map
during readdir operations has cause lockdep to have a heart attack
as it now sees a different locking order on inodes w.r.t. the
mmap_sem because readdir has a different ordering to write().

Add a new lockdep class for directory inodes to avoid this false
positive.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_iops.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 9ddfb81..bb3bb65 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -48,6 +48,18 @@
 #include <linux/fiemap.h>
 #include <linux/slab.h>
 
+/*
+ * Directories have different lock order w.r.t. mmap_sem compared to regular
+ * files. This is due to readdir potentially triggering page faults on a user
+ * buffer inside filldir(), and this happens with the ilock on the directory
+ * held. For regular files, the lock order is the other way around - the
+ * mmap_sem is taken during the page fault, and then we lock the ilock to do
+ * block mapping. Hence we need a different class for the directory ilock so
+ * that lockdep can tell them apart.
+ */
+static struct lock_class_key xfs_nondir_ilock_class;
+static struct lock_class_key xfs_dir_ilock_class;
+
 static int
 xfs_initxattrs(
        struct inode            *inode,
@@ -1191,6 +1203,7 @@ xfs_setup_inode(
        xfs_diflags_to_iflags(inode, ip);
 
        ip->d_ops = ip->i_mount->m_nondir_inode_ops;
+       lockdep_set_class(&ip->i_lock.mr_lock, &xfs_nondir_ilock_class);
        switch (inode->i_mode & S_IFMT) {
        case S_IFREG:
                inode->i_op = &xfs_inode_operations;
@@ -1198,6 +1211,7 @@ xfs_setup_inode(
                inode->i_mapping->a_ops = &xfs_address_space_operations;
                break;
        case S_IFDIR:
+               lockdep_set_class(&ip->i_lock.mr_lock, &xfs_dir_ilock_class);
                if (xfs_sb_version_hasasciici(&XFS_M(inode->i_sb)->m_sb))
                        inode->i_op = &xfs_dir_ci_inode_operations;
                else
-- 
1.8.4.rc3

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