[PATCH] Fix sync. in inode_has_no_xattr()

[Alexander Lochmann]

inode.i_flags might be altered without proper
synchronisation when the inode belongs to devtmpfs.
The following stacktrace shows how to get there:
13: entry_SYSENTER_32:460
12: do_fast_syscall_32:410
11: _static_cpu_has:146
10: do_syscall_32_irqs_on:322
09: SyS_pwrite64:636
08: SYSC_pwrite64:650
07: fdput:38
06: vfs_write:560
05: __vfs_write:512
04: new_sync_write:500
03: blkdev_write_iter:1977
02: __generic_file_write_iter:2897
01: file_remove_privs:1818
00: inode_has_no_xattr:3163

Found by LockDoc (Alexander Lochmann, Horst Schirmeier and Olaf
Spinczyk)

Signed-off-by: Alexander Lochmann <alexander.lochmann@xxxxxxxxxxxxxx>
Signed-off-by: Horst Schirmeier <horst.schirmeier@xxxxxxxxxxxxxx>
---
 include/linux/fs.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index c95c0807471f..40722678d741 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3443,10 +3443,14 @@ static inline int check_sticky(struct inode
*dir, struct inode *inode)
 	return __check_sticky(dir, inode);
 }

+/*
+ * blkdev_write_iter() can call this without i_rwsem, need to be
+ * careful with i_flags update.
+ */
 static inline void inode_has_no_xattr(struct inode *inode)
 {
 	if (!is_sxid(inode->i_mode) && (inode->i_sb->s_flags & SB_NOSEC))
-		inode->i_flags |= S_NOSEC;
+		inode_set_flags(inode, S_NOSEC, S_NOSEC);
 }

 static inline bool is_root_inode(struct inode *inode)
-- 
2.19.1

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