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Re: [PATCH 1/2] direct-io: move aio_complete into ->end_io

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH 1/2] direct-io: move aio_complete into ->end_io
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 24 Jun 2010 23:59:22 +0200
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx
In-reply-to: <20100622123113.011371666@xxxxxxxxxxxxxxxxxxxxxx>
References: <20100622122144.302857146@xxxxxxxxxxxxxxxxxxxxxx> <20100622123113.011371666@xxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Tue 22-06-10 08:21:45, Christoph Hellwig wrote:
> Filesystems with unwritten extent support must not complete an AIO request
> until the transaction to convert the extent has been commited.  That means
> the aio_complete calls needs to be moved into the ->end_io callback so
> that the filesystem can control when to call it exactly.
> 
> This makes a bit of a mess out of dio_complete and the ->end_io callback
> prototype even more complicated.  In addition ->end_io is now called with
> i_alloc_sem held for DIO_LOCKING filesystems.  The only filesystem that
> has both and ->end_io callback and sets DIO_LOCKING is ext4, which doesn't
> appear to do anything that could deadlock with i_alloc_sem in ->end_io.
  Umm, I don't get this. Looking at the ->end_io callback it has been
always called with i_alloc_sem held. It's only aio_complete() which will
be called with i_alloc_sem held after your changes. Or am I missing
something?
  Moreover the async testing you do does not seem to be completely right.
dio->is_async is a flag that controls whether dio code waits for IO to be
completed or not. In particular it is not set for AIO that spans beyond
current i_size so it does not seem to be exactly what you need (at least
for ext4 it isn't). I think that is_sync_kiocb() is a test that should be
used to recognize AIO - and that has an advantage that you don't have to
pass the is_async flag around.

                                                                Honza
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> 
> Index: linux-2.6/fs/direct-io.c
> ===================================================================
> --- linux-2.6.orig/fs/direct-io.c     2010-06-22 09:48:37.239004298 +0200
> +++ linux-2.6/fs/direct-io.c  2010-06-22 11:54:42.281003878 +0200
> @@ -218,7 +218,7 @@ static struct page *dio_get_page(struct
>   * filesystems can use it to hold additional state between get_block calls 
> and
>   * dio_complete.
>   */
> -static int dio_complete(struct dio *dio, loff_t offset, int ret)
> +static int dio_complete(struct dio *dio, loff_t offset, int ret, bool 
> is_async)
>  {
>       ssize_t transferred = 0;
>  
> @@ -239,14 +239,6 @@ static int dio_complete(struct dio *dio,
>                       transferred = dio->i_size - offset;
>       }
>  
> -     if (dio->end_io && dio->result)
> -             dio->end_io(dio->iocb, offset, transferred,
> -                         dio->map_bh.b_private);
> -
> -     if (dio->flags & DIO_LOCKING)
> -             /* lockdep: non-owner release */
> -             up_read_non_owner(&dio->inode->i_alloc_sem);
> -
>       if (ret == 0)
>               ret = dio->page_errors;
>       if (ret == 0)
> @@ -254,6 +246,17 @@ static int dio_complete(struct dio *dio,
>       if (ret == 0)
>               ret = transferred;
>  
> +     if (dio->end_io && dio->result) {
> +             dio->end_io(dio->iocb, offset, transferred,
> +                         dio->map_bh.b_private, ret, is_async);
> +     } else if (is_async) {
> +             aio_complete(dio->iocb, ret, 0);
> +     }
> +
> +     if (dio->flags & DIO_LOCKING)
> +             /* lockdep: non-owner release */
> +             up_read_non_owner(&dio->inode->i_alloc_sem);
> +
>       return ret;
>  }
>  
> @@ -277,8 +280,7 @@ static void dio_bio_end_aio(struct bio *
>       spin_unlock_irqrestore(&dio->bio_lock, flags);
>  
>       if (remaining == 0) {
> -             int ret = dio_complete(dio, dio->iocb->ki_pos, 0);
> -             aio_complete(dio->iocb, ret, 0);
> +             dio_complete(dio, dio->iocb->ki_pos, 0, true);
>               kfree(dio);
>       }
>  }
> @@ -1126,7 +1128,7 @@ direct_io_worker(int rw, struct kiocb *i
>       spin_unlock_irqrestore(&dio->bio_lock, flags);
>  
>       if (ret2 == 0) {
> -             ret = dio_complete(dio, offset, ret);
> +             ret = dio_complete(dio, offset, ret, false);
>               kfree(dio);
>       } else
>               BUG_ON(ret != -EIOCBQUEUED);
> Index: linux-2.6/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/inode.c    2010-06-22 09:48:37.249004508 +0200
> +++ linux-2.6/fs/ext4/inode.c 2010-06-22 12:18:45.883255381 +0200
> @@ -3775,7 +3775,8 @@ static ext4_io_end_t *ext4_init_io_end (
>  }
>  
>  static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> -                         ssize_t size, void *private)
> +                         ssize_t size, void *private, int ret,
> +                         bool is_async)
>  {
>          ext4_io_end_t *io_end = iocb->private;
>       struct workqueue_struct *wq;
> @@ -3784,7 +3785,7 @@ static void ext4_end_io_dio(struct kiocb
>  
>       /* if not async direct IO or dio with 0 bytes write, just return */
>       if (!io_end || !size)
> -             return;
> +             goto out;
>  
>       ext_debug("ext4_end_io_dio(): io_end 0x%p"
>                 "for inode %lu, iocb 0x%p, offset %llu, size %llu\n",
> @@ -3795,7 +3796,7 @@ static void ext4_end_io_dio(struct kiocb
>       if (io_end->flag != EXT4_IO_UNWRITTEN){
>               ext4_free_io_end(io_end);
>               iocb->private = NULL;
> -             return;
> +             goto out;
>       }
>  
>       io_end->offset = offset;
> @@ -3812,6 +3813,9 @@ static void ext4_end_io_dio(struct kiocb
>       list_add_tail(&io_end->list, &ei->i_completed_io_list);
>       spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
>       iocb->private = NULL;
> +out:
> +     if (is_async)
> +             aio_complete(iocb, ret, 0);
>  }
>  
>  static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
> Index: linux-2.6/fs/ocfs2/aops.c
> ===================================================================
> --- linux-2.6.orig/fs/ocfs2/aops.c    2010-06-22 09:48:37.259012749 +0200
> +++ linux-2.6/fs/ocfs2/aops.c 2010-06-22 12:19:03.931005757 +0200
> @@ -609,7 +609,9 @@ bail:
>  static void ocfs2_dio_end_io(struct kiocb *iocb,
>                            loff_t offset,
>                            ssize_t bytes,
> -                          void *private)
> +                          void *private,
> +                          int ret,
> +                          bool is_async)
>  {
>       struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
>       int level;
> @@ -623,6 +625,9 @@ static void ocfs2_dio_end_io(struct kioc
>       if (!level)
>               up_read(&inode->i_alloc_sem);
>       ocfs2_rw_unlock(inode, level);
> +
> +     if (is_async)
> +             aio_complete(iocb, ret, 0);
>  }
>  
>  /*
> Index: linux-2.6/fs/xfs/linux-2.6/xfs_aops.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/linux-2.6/xfs_aops.c        2010-06-22 
> 09:48:37.268012190 +0200
> +++ linux-2.6/fs/xfs/linux-2.6/xfs_aops.c     2010-06-22 14:05:02.522005722 
> +0200
> @@ -1599,7 +1599,9 @@ xfs_end_io_direct(
>       struct kiocb    *iocb,
>       loff_t          offset,
>       ssize_t         size,
> -     void            *private)
> +     void            *private,
> +     int             ret,
> +     bool            is_async)
>  {
>       xfs_ioend_t     *ioend = iocb->private;
>  
> @@ -1645,6 +1647,9 @@ xfs_end_io_direct(
>        * against double-freeing.
>        */
>       iocb->private = NULL;
> +
> +     if (is_async)
> +             aio_complete(iocb, ret, 0);
>  }
>  
>  STATIC ssize_t
> Index: linux-2.6/fs/xfs/linux-2.6/xfs_aops.h
> ===================================================================
> --- linux-2.6.orig/fs/xfs/linux-2.6/xfs_aops.h        2010-06-22 
> 09:48:37.278274238 +0200
> +++ linux-2.6/fs/xfs/linux-2.6/xfs_aops.h     2010-06-22 09:49:12.388034051 
> +0200
> @@ -37,6 +37,8 @@ typedef struct xfs_ioend {
>       size_t                  io_size;        /* size of the extent */
>       xfs_off_t               io_offset;      /* offset in the file */
>       struct work_struct      io_work;        /* xfsdatad work queue */
> +     struct kiocb            *io_iocb;
> +     int                     io_result;
>  } xfs_ioend_t;
>  
>  extern const struct address_space_operations xfs_address_space_operations;
> Index: linux-2.6/include/linux/fs.h
> ===================================================================
> --- linux-2.6.orig/include/linux/fs.h 2010-06-22 09:49:07.188253984 +0200
> +++ linux-2.6/include/linux/fs.h      2010-06-22 10:34:10.128005975 +0200
> @@ -415,7 +415,8 @@ struct buffer_head;
>  typedef int (get_block_t)(struct inode *inode, sector_t iblock,
>                       struct buffer_head *bh_result, int create);
>  typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> -                     ssize_t bytes, void *private);
> +                     ssize_t bytes, void *private, int ret,
> +                     bool is_async);
>  
>  /*
>   * Attribute flags.  These should be or-ed together to figure out what
> 
> --
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-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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