On Wed, 05 Sep 2012 20:59:09 +0400, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote:
> 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()
Yeah... This is not just my fault :)
Similar deadlock already exist but happen due to end_io_work
truncate: kworker:
ext4_setattr ext4_end_io_work
mutex_lock(i_mutex)
inode_dio_wait(inode) ->BLOCK
DEADLOCK<- mutex_trylock()
inode_dio_done()
#TEST_CASE
MNT=/mnt_scrach
unlink $MNT/file
fallocate -l $((1024*1024*1024)) $MNT/file
aio-stress -I 100000 -O -s 100m -n -t 1 -c 10 -o 2 -o 3 $MNT/file &
sleep 3
truncate -s 0 $MNT/file
#TEST_CASE_END
>
> 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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