linux-kernel - [PATCH 3.16 097/114] xfs: mmap lock needs to be inside freeze protection

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Message-ID: <lsq.1465842997.733859592@decadent.org.uk>
Date:	Mon, 13 Jun 2016 19:36:37 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Brian Foster" <bfoster@...hat.com>,
	"Dave Chinner" <dchinner@...hat.com>,
	"Dave Chinner" <david@...morbit.com>, xfs@....sgi.com,
	"Jan Kara" <jack@...e.cz>
Subject: [PATCH 3.16 097/114] xfs: mmap lock needs to be inside freeze
 protection

3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Dave Chinner <dchinner@...hat.com>

commit ec56b1f1fdc69599963574ce94cc5693d535dd64 upstream.

Lock ordering for the new mmap lock needs to be:

mmap_sem
  sb_start_pagefault
    i_mmap_lock
      page lock
        <fault processsing>

Right now xfs_vm_page_mkwrite gets this the wrong way around,
While technically it cannot deadlock due to the current freeze
ordering, it's still a landmine that might explode if we change
anything in future. Hence we need to nest the locks correctly.

Signed-off-by: Dave Chinner <dchinner@...hat.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Reviewed-by: Brian Foster <bfoster@...hat.com>
Signed-off-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Cc: Jan Kara <jack@...e.cz>
Cc: xfs@....sgi.com
---
 fs/xfs/xfs_file.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1441,15 +1441,20 @@ xfs_filemap_page_mkwrite(
 	struct vm_fault		*vmf)
 {
 	struct xfs_inode	*ip = XFS_I(vma->vm_file->f_mapping->host);
-	int			error;
+	int			ret;
 
 	trace_xfs_filemap_page_mkwrite(ip);
 
+	sb_start_pagefault(VFS_I(ip)->i_sb);
+	file_update_time(vma->vm_file);
 	xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
-	error = block_page_mkwrite(vma, vmf, xfs_get_blocks);
+
+	ret = __block_page_mkwrite(vma, vmf, xfs_get_blocks);
+
 	xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
+	sb_end_pagefault(VFS_I(ip)->i_sb);
 
-	return error;
+	return block_page_mkwrite_return(ret);
 }
 
 const struct file_operations xfs_file_operations = {