[PATCH] fs: clear writeback errors in inode_init_always

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

In inode_init_always(), we clear the inode mapping flags, which clears
any retained error (AS_EIO, AS_ENOSC) bits.  Unfortunately, we do not
also clear wb_err, which means that old mapping errors can leak through
to new inodes.

This is crucial for the XFS inode allocation path because we recycle old
in-core inodes and we do not want error state from an old file to leak
into the new file.  This bug was discovered by running generic/036 and
generic/047 in a loop and noticing that the EIOs generated by the
collision of direct and buffered writes in generic/036 would survive the
remount between 036 and 047, and get reported to the fsyncs (on
different files on a reformatted fs!) in generic/047.

Since we're changing the semantics of inode_init_always, we must also
change xfs_reinit_inode to retain the writeback error state when we go
to recover an inode that has been torn down in the vfs but not yet
disposed of by XFS.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/inode.c          |    1 +
 fs/xfs/xfs_icache.c |    2 ++
 2 files changed, 3 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index 13ceb98c3bd3..3b55391072f3 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -178,6 +178,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	mapping->a_ops = &empty_aops;
 	mapping->host = inode;
 	mapping->flags = 0;
+	mapping->wb_err = 0;
 	atomic_set(&mapping->i_mmap_writable, 0);
 	mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
 	mapping->private_data = NULL;
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index 164350d91efc..f4d672cb60a4 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -298,6 +298,7 @@ xfs_reinit_inode(
 	uint64_t	version = inode_peek_iversion(inode);
 	umode_t		mode = inode->i_mode;
 	dev_t		dev = inode->i_rdev;
+	errseq_t	old_err = inode->i_mapping->wb_err;
 
 	error = inode_init_always(mp->m_super, inode);
 
@@ -306,6 +307,7 @@ xfs_reinit_inode(
 	inode_set_iversion_queried(inode, version);
 	inode->i_mode = mode;
 	inode->i_rdev = dev;
+	inode->i_mapping->wb_err = old_err;
 	return error;
 }