[PATCH] gfs2: fiemap page fault fix

In gfs2_fiemap(), we are calling iomap_fiemap() while holding the inode
glock.  This can lead to recursive glock taking if the fiemap buffer is
memory mapped to the same inode and accessing it triggers a page fault.

Fix by disabling page faults for iomap_fiemap() and faulting in the
buffer by hand if necessary.

Fixes xfstest generic/742.

Signed-off-by: Andreas Gruenbacher <[email protected]>
---
 fs/gfs2/inode.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/gfs2/inode.c b/fs/gfs2/inode.c
index b6ed069b3487..4d65e4a75262 100644
--- a/fs/gfs2/inode.c
+++ b/fs/gfs2/inode.c
@@ -2192,6 +2192,14 @@ static int gfs2_getattr(struct mnt_idmap *idmap,
 	return 0;
 }
 
+static bool fault_in_fiemap(struct fiemap_extent_info *fi)
+{
+	struct fiemap_extent __user *dest = fi->fi_extents_start;
+	size_t size = sizeof(*dest) * fi->fi_extents_max;
+
+	return fault_in_safe_writeable((char __user *)dest, size) == 0;
+}
+
 static int gfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		       u64 start, u64 len)
 {
@@ -2201,14 +2209,22 @@ static int gfs2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 	inode_lock_shared(inode);
 
+retry:
 	ret = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
 	if (ret)
 		goto out;
 
+	pagefault_disable();
 	ret = iomap_fiemap(inode, fieinfo, start, len, &gfs2_iomap_ops);
+	pagefault_enable();
 
 	gfs2_glock_dq_uninit(&gh);
 
+	if (ret == -EFAULT && fault_in_fiemap(fieinfo)) {
+		fieinfo->fi_extents_mapped = 0;
+		goto retry;
+	}
+
 out:
 	inode_unlock_shared(inode);
 	return ret;
-- 
2.52.0