Patch "NFS: Don't let the ctime override attribute barriers." has been added to the 4.2-stable tree

This is a note to let you know that I've just added the patch titled

NFS: Don't let the ctime override attribute barriers.

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
nfs-don-t-let-the-ctime-override-attribute-barriers.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Trond Myklebust <[email protected]>
Date: Thu, 6 Aug 2015 12:06:30 -0400
Subject: NFS: Don't let the ctime override attribute barriers.

From: Trond Myklebust <[email protected]>

commit 7c2dad99d60c86ec686b3bfdcb787c450a7ea89f upstream.

Chuck reports seeing cases where a GETATTR that happens to race with an asynchronous WRITE is overriding the file size, despite the attribute barrier being set by the writeback code.

The culprit turns out to be the check in nfs_ctime_need_update(), which sees that the ctime is newer than the cached ctime, and assumes that it is safe to override the attribute barrier. This patch removes that override, and ensures that attribute barriers are always respected.

---
 fs/nfs/inode.c |    8 --------
 1 file changed, 8 deletions(-)

@@ -1273,13 +1273,6 @@ static int nfs_check_inode_attributes(st
 	return 0;
 }
 
-static int nfs_ctime_need_update(const struct inode *inode, const struct nfs_fattr *fattr)
-{
-	if (!(fattr->valid & NFS_ATTR_FATTR_CTIME))
-		return 0;
-	return timespec_compare(&fattr->ctime, &inode->i_ctime) > 0;
-}
-
 static atomic_long_t nfs_attr_generation_counter;
 
 static unsigned long nfs_read_attr_generation_counter(void)

@@ -1428,7 +1421,6 @@ static int nfs_inode_attrs_need_update(c
 	const struct nfs_inode *nfsi = NFS_I(inode);
 
 	return ((long)fattr->gencount - (long)nfsi->attr_gencount) > 0 ||
-		nfs_ctime_need_update(inode, fattr) ||
 		((long)nfsi->attr_gencount - (long)nfs_read_attr_generation_counter() > 0);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/nfs-don-t-let-the-ctime-override-attribute-barriers.patch queue-4.2/nfsv4-don-t-set-setattr-for-o_rdonly-o_excl.patch queue-4.2/nfsv4.1-pnfs-fix-borken-function-_same_data_server_addrs_locked.patch queue-4.2/nfsv4.1-pnfs-fix-atomicity-of-commit-list-updates.patch