Fixes for 4.19

[thirdparty/kernel/stable-queue.git] / releases / 2.6.27.36 / fs-make-sure-data-stored-into-inode-is-properly-seen-before-unlocking-new-inode.patch

From 580be0837a7a59b207c3d5c661d044d8dd0a6a30 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Mon, 21 Sep 2009 17:01:06 -0700
Subject: fs: make sure data stored into inode is properly seen before unlocking new inode

From: Jan Kara <jack@suse.cz>

commit 580be0837a7a59b207c3d5c661d044d8dd0a6a30 upstream.

In theory it could happen that on one CPU we initialize a new inode but
clearing of I_NEW | I_LOCK gets reordered before some of the
initialization.  Thus on another CPU we return not fully uptodate inode
from iget_locked().

This seems to fix a corruption issue on ext3 mounted over NFS.

[akpm@linux-foundation.org: add some commentary]
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 fs/inode.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/fs/inode.c
+++ b/fs/inode.c
@@ -590,13 +590,15 @@ void unlock_new_inode(struct inode *inod
 	}
 #endif
 	/*
-	 * This is special!  We do not need the spinlock
-	 * when clearing I_LOCK, because we're guaranteed
-	 * that nobody else tries to do anything about the
-	 * state of the inode when it is locked, as we
-	 * just created it (so there can be no old holders
-	 * that haven't tested I_LOCK).
+	 * This is special!  We do not need the spinlock when clearing I_LOCK,
+	 * because we're guaranteed that nobody else tries to do anything about
+	 * the state of the inode when it is locked, as we just created it (so
+	 * there can be no old holders that haven't tested I_LOCK).
+	 * However we must emit the memory barrier so that other CPUs reliably
+	 * see the clearing of I_LOCK after the other inode initialisation has
+	 * completed.
 	 */
+	smp_mb();
 	WARN_ON((inode->i_state & (I_LOCK|I_NEW)) != (I_LOCK|I_NEW));
 	inode->i_state &= ~(I_LOCK|I_NEW);
 	wake_up_inode(inode);