Andrew Morton <[email protected]> writes:
> On Mon, 11 Dec 2006 16:34:27 +0300
> Dmitriy Monakhov <[email protected]> wrote:
>
>> OpenVZ team has discovered error inside generic_file_direct_write()
>> If generic_file_direct_IO() has fail (ENOSPC condition) it may have instantiated
>> a few blocks outside i_size. And fsck will complain about wrong i_size
>> (ext2, ext3 and reiserfs interpret i_size and biggest block difference as error),
>> after fsck will fix error i_size will be increased to the biggest block,
>> but this blocks contain gurbage from previous write attempt, this is not
>> information leak, but its silence file data corruption.
>> We need truncate any block beyond i_size after write have failed , do in simular
>> generic_file_buffered_write() error path.
>>
>> Exampe:
>> open("mnt2/FILE3", O_WRONLY|O_CREAT|O_DIRECT, 0666) = 3
>> write(3, "aaaaaa"..., 4096) = -1 ENOSPC (No space left on device)
>>
>> stat mnt2/FILE3
>> File: `mnt2/FILE3'
>> Size: 0 Blocks: 4 IO Block: 4096 regular empty file
>> >>>>>>>>>>>>>>>>>>>>>>^^^^^^^^^^ file size is less than biggest block idx
>> Device: 700h/1792d Inode: 14 Links: 1
>> Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
>>
>> fsck.ext2 -f -n mnt1/fs_img
>> Pass 1: Checking inodes, blocks, and sizes
>> Inode 14, i_size is 0, should be 2048. Fix? no
>>
>> Signed-off-by: Dmitriy Monakhov <[email protected]>
>> ----------
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 7b84dc8..bf7cf6c 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -2041,6 +2041,14 @@ generic_file_direct_write(struct kiocb *
>> mark_inode_dirty(inode);
>> }
>> *ppos = end;
>> + } else if (written < 0) {
>> + loff_t isize = i_size_read(inode);
>> + /*
>> + * generic_file_direct_IO() may have instantiated a few blocks
>> + * outside i_size. Trim these off again.
>> + */
>> + if (pos + count > isize)
>> + vmtruncate(inode, isize);
>> }
>>
>
> XFS (at least) can call generic_file_direct_write() with i_mutex not held.
How could it be ?
from mm/filemap.c:2046 generic_file_direct_write() comment right after
place where i want to add vmtruncate()
/*
* Sync the fs metadata but not the minor inode changes and
* of course not the data as we did direct DMA for the IO.
* i_mutex is held, which protects generic_osync_inode() from
* livelocking.
*/
> And vmtruncate() expects i_mutex to be held.
generic_file_direct_IO must called under i_mutex too
from mm/filemap.c:2388
/*
* Called under i_mutex for writes to S_ISREG files. Returns -EIO if something
* went wrong during pagecache shootdown.
*/
static ssize_t
generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
This means XFS generic_file_direct_write() call generic_file_direct_IO() without
i_mutex held too?
>
> I guess a suitable solution would be to push this problem back up to the
> callers: let them decide whether to run vmtruncate() and if so, to ensure
> that i_mutex is held.
>
> The existence of generic_file_aio_write_nolock() makes that rather messy
> though.
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