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

Jan Kara
2010-06-24T21:57:11Z

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@lst.de>
>
> 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@suse.cz>
SUSE Labs, CR