[Ocfs2-devel] ocfs2: fix sparse file & data ordering issue in direct io

[piaojun <piaojun@huawei.com>]

Hi Carpenter,

I guess this may cause illegal memory access error as follows:

generic_perform_write
--a_ops->write_begin(file, mapping, pos, bytes, flags, &page, &fsdata);
  --ocfs2_write_begin_nolock
    --ocfs2_grab_pages_for_write
	--return -EAGAIN if not enough pages
    --'fsdata' will be uninitialized

--a_ops->write_end(file, mapping, pos, bytes, copied, page, fsdata);
  --ocfs2_write_end_nolock
    --the access of wc->w_di_bh->b_data will cause error.

if so, I suggest not eating error code and let upper level to handle
this problem.

On 2016-3-9 18:25, Dan Carpenter wrote:
> Hello Ryan Ding,
> 
> The patch fbe25fb91af5: "ocfs2: fix sparse file & data ordering issue
> in direct io" from Feb 25, 2016, leads to the following static
> checker warning:
> 
> 	fs/ocfs2/aops.c:2242 ocfs2_dio_get_block()
> 	error: potentially dereferencing uninitialized 'wc'.
> 
> fs/ocfs2/aops.c
>   2235  
>   2236          ret = ocfs2_write_begin_nolock(inode->i_mapping, pos, len,
>   2237                                         OCFS2_WRITE_DIRECT, NULL,
>   2238                                         (void **)&wc, di_bh, NULL);
>                                                ^^^^^^^^^^^^
> 
> See commit 5cffff9e2986 ('ocfs2: Fix ocfs2_page_mkwrite()') for an
> explanation why a zero return here does not imply that "wc" has been
> initialized.
> 
>   2239          if (ret) {
>   2240                  mlog_errno(ret);
>   2241                  goto unlock;
>   2242          }
>   2243  
>   2244          desc = &wc->w_desc[0];
>   2245  
>   2246          p_blkno = ocfs2_clusters_to_blocks(inode->i_sb, desc->c_phys);
> 
> regards,
> dan carpenter
> 
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