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[PATCH 1/8] xfs: mmap lock needs to be inside freeze protection

To: xfs@xxxxxxxxxxx
Subject: [PATCH 1/8] xfs: mmap lock needs to be inside freeze protection
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 24 Mar 2015 21:50:59 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, willy@xxxxxxxxxxxxxxx, jack@xxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1427194266-2885-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1427194266-2885-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 fs/xfs/xfs_file.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index dc5f609..a4c882e 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1449,15 +1449,20 @@ 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 = {
-- 
2.0.0

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