On Wed, 5 Sep 2012 17:49:20 +0200, Jan Kara <jack@xxxxxxx> wrote:
> On Tue 04-09-12 21:36:54, Dmitry Monakhov wrote:
> > Jan Kara have spotted interesting issue:
> > There are potential data corruption issue with direct IO overwrites
> > racing with truncate:
> > Like:
> > dio write truncate_task
> > ->ext4_ext_direct_IO
> > ->overwrite == 1
> > ->down_read(&EXT4_I(inode)->i_data_sem);
> > ->mutex_unlock(&inode->i_mutex);
> > ->ext4_setattr()
> > ->inode_dio_wait()
> > ->truncate_setsize()
> > ->ext4_truncate()
> > ->down_write(&EXT4_I(inode)->i_data_sem);
> > ->__blockdev_direct_IO
> > ->ext4_get_block
> > ->submit_io()
> > ->up_read(&EXT4_I(inode)->i_data_sem);
> > # truncate data blocks, allocate them to
> > # other inode - bad stuff happens because
> > # dio is still in flight.
> >
> > In order to serialize with truncate dio worker should grab extra i_dio_count
> > reference before drop i_mutex.
> Thanks for the patch. You can add:
> Reviewed-by: Jan Kara <jack@xxxxxxx>
I'm Sorry, but unfortunately in two line patch i've done one mistake :(
because inode_dio_done() should be before i_mutex will be retaken
otherwise following deadlock happen
ext4_setattr ext4_direct_io
mutex_unlock
atomic_inc(inode->i_dio_count)
mutex_lock(i_mutex)
inode_dio_wait(inode) ->BLOCK
DEADLOCK<- mutex_lock(i_mutex)
inode_dio_done()
So i'll add your review sing to updated version if you don't mind.
> Honza
> > Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> > ---
> > fs/ext4/inode.c | 2 ++
> > 1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 5a75908..9725acb 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -3035,6 +3035,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> > overwrite = *((int *)iocb->private);
> >
> > if (overwrite) {
> > + atomic_inc(&inode->i_dio_count);
> > down_read(&EXT4_I(inode)->i_data_sem);
> > mutex_unlock(&inode->i_mutex);
> > }
> > @@ -3134,6 +3135,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> > if (overwrite) {
> > up_read(&EXT4_I(inode)->i_data_sem);
> > mutex_lock(&inode->i_mutex);
> > + inode_dio_done(inode);
> > }
> >
> > return ret;
> > --
> > 1.7.7.6
> >
> --
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
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