Messages in this thread | | | Subject | Re: [PATCH] incorrect error handling inside generic_file_direct_write | From | Dmitriy Monakhov <> | Date | Tue, 12 Dec 2006 12:22:14 +0300 |
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Andrew Morton <akpm@osdl.org> writes:
> On Mon, 11 Dec 2006 16:34:27 +0300 > Dmitriy Monakhov <dmonakhov@openvz.org> 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 <dmonakhov@openvz.org> >> ---------- >> >> 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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