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Re: [PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correc

To: Jeff Moyer <jmoyer@xxxxxxxxxx>
Subject: Re: [PATCH 9/9] blkdev: Fix up AIO+DIO+O_SYNC to do the sync part correctly
From: Jan Kara <jack@xxxxxxx>
Date: Wed, 21 Nov 2012 01:57:39 +0100
Cc: Jan Kara <jack@xxxxxxx>, "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>, axboe@xxxxxxxxx, tytso@xxxxxxx, david@xxxxxxxxxxxxx, bpm@xxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, hch@xxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <x49obishuh1.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <20121120074116.24645.36369.stgit@xxxxxxxxxxxxxxxxxxx> <20121120075115.25270.62451.stgit@xxxxxxxxxxxxxxxxxxx> <20121120101559.GC1408@xxxxxxxxxxxxx> <x49obishuh1.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue 20-11-12 15:47:54, Jeff Moyer wrote:
> Jan Kara <jack@xxxxxxx> writes:
> 
> > On Mon 19-11-12 23:51:15, Darrick J. Wong wrote:
> >> When performing O_SYNC+AIO+DIO writes to block devices, use the 
> >> DIO_SYNC_WRITES
> >> flag so that flushes are issued /after/ the write completes, not before.
> >> 
> >> Note, however, that for block devices, the DIO setup code ensures that a 
> >> flush
> >> wq is attached to the superblock of the bdevfs filesystem, not the 
> >> filesystem
> >> that the device node happens to reside in.  This means that unlike regular
> >> files, iocb->ki_filp->f_mapping->host->i_sb != inode->i_sb.  Therefore, 
> >> adjust
> >> Jeff's earlier patch to keep the pointer use consistent and avoid a NULL 
> >> deref.
> >> 
> >> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >> ---
> >>  fs/block_dev.c |    5 +++--
> >>  fs/direct-io.c |    3 ++-
> >>  2 files changed, 5 insertions(+), 3 deletions(-)
> >> 
> >> 
> >> diff --git a/fs/block_dev.c b/fs/block_dev.c
> >> index 1a1e5e3..05ff33a 100644
> >> --- a/fs/block_dev.c
> >> +++ b/fs/block_dev.c
> >> @@ -235,7 +235,8 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const 
> >> struct iovec *iov,
> >>    struct inode *inode = file->f_mapping->host;
> >>  
> >>    return __blockdev_direct_IO(rw, iocb, inode, I_BDEV(inode), iov, offset,
> >> -                              nr_segs, blkdev_get_blocks, NULL, NULL, 0);
> >> +                              nr_segs, blkdev_get_blocks, NULL, NULL,
> >> +                              DIO_SYNC_WRITES);
> >>  }
> >>  
> >>  int __sync_blockdev(struct block_device *bdev, int wait)
> >> @@ -1631,7 +1632,7 @@ ssize_t blkdev_aio_write(struct kiocb *iocb, const 
> >> struct iovec *iov,
> >>    percpu_down_read(&bdev->bd_block_size_semaphore);
> >>  
> >>    ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
> >> -  if (ret > 0 || ret == -EIOCBQUEUED) {
> >> +  if (ret > 0) {
> >>            ssize_t err;
> >>  
> >>            err = generic_write_sync(file, pos, ret);
> >> diff --git a/fs/direct-io.c b/fs/direct-io.c
> >> index b7391d4..c626c43 100644
> >> --- a/fs/direct-io.c
> >> +++ b/fs/direct-io.c
> >> @@ -258,7 +258,8 @@ void generic_dio_end_io(struct kiocb *iocb, loff_t 
> >> offset, ssize_t bytes,
> >>            work->ret = ret;
> >>            work->offset = offset;
> >>            work->len = bytes;
> >> -          queue_work(inode->i_sb->s_dio_flush_wq, &work->work);
> >> +          queue_work(iocb->ki_filp->f_mapping->host->i_sb->s_dio_flush_wq,
> >> +                     &work->work);
> >   This should be folded into the original patch introducing the
> > s_dio_flush_wq. And please add a comment before this line saying that block
> > devices need a dereference exactly like this... Otherwise the patch looks
> > good so you can add:
> >   Reviewed-by: Jan Kara <jack@xxxxxxx>
> 
> When you say, "This," do you mean that one change, or the whole patch?
  I meant the whole patch after that hung is folded ;)

                                                                Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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