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Date: Wed, 28 Aug 2019 21:59:14 +0200
From: Jan Kara <jack@...e.cz>
To: Matthew Bobrowski <mbobrowski@...browski.org>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
jack@...e.cz, tytso@....edu, riteshh@...ux.ibm.com
Subject: Re: [PATCH 2/5] ext4: move inode extension/truncate code out from
ext4_iomap_end()
On Mon 12-08-19 22:52:53, Matthew Bobrowski wrote:
> In preparation for implementing the direct IO write code path modifications
> that make us of iomap infrastructure we need to move out the inode
> extension/truncate code from ext4_iomap_end() callback. For direct IO, if the
> current code remained it would behave incorrectly. If we update the inode size
> prior to converting unwritten extents we run the risk of allowing a racing
> direct IO read operation to find unwritten extents before they are converted.
>
> The inode extension/truncate has been moved out into a new function
> ext4_handle_inode_extension(). This will be used by both direct IO and DAX
> code paths if the write results with the inode being extended.
>
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>
> ---
> fs/ext4/file.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> fs/ext4/inode.c | 48 +--------------------------------------------
> 2 files changed, 60 insertions(+), 48 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 360eff7b6aa2..7470800c63b7 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -33,6 +33,7 @@
> #include "ext4_jbd2.h"
> #include "xattr.h"
> #include "acl.h"
> +#include "truncate.h"
>
> static bool ext4_dio_checks(struct inode *inode)
> {
> @@ -234,12 +235,62 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
> return iov_iter_count(from);
> }
>
> +static int ext4_handle_inode_extension(struct inode *inode, loff_t size,
> + size_t count)
> +{
> + handle_t *handle;
> + bool truncate = false;
> + ext4_lblk_t written_blk, end_blk;
> + int ret = 0, blkbits = inode->i_blkbits;
> +
> + handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
> + if (IS_ERR(handle)) {
> + ret = PTR_ERR(handle);
> + goto orphan_del;
> + }
> +
> + if (ext4_update_inode_size(inode, size))
> + ext4_mark_inode_dirty(handle, inode);
> +
> + /*
> + * We may need truncate allocated but not written blocks
> + * beyond EOF.
> + */
> + written_blk = ALIGN(size, 1 << blkbits);
> + end_blk = ALIGN(size + count, 1 << blkbits);
So this seems to imply that 'size' is really offset where IO started but
ext4_update_inode_size(inode, size) above suggests 'size' is really where
IO has ended and that's indeed what you pass into
ext4_handle_inode_extension(). So I'd just make the calling convention for
ext4_handle_inode_extension() less confusing and pass 'offset' and 'len'
and fixup the math inside the function...
Otherwise the patch looks OK to me.
Honza
> + if (written_blk < end_blk && ext4_can_truncate(inode))
> + truncate = true;
> +
> + /*
> + * Remove the inode from the orphan list if it has been
> + * extended and everything went OK.
> + */
> + if (!truncate && inode->i_nlink)
> + ext4_orphan_del(handle, inode);
> + ext4_journal_stop(handle);
> +
> + if (truncate) {
> + ext4_truncate_failed_write(inode);
> +orphan_del:
> + /*
> + * If the truncate operation failed early the inode
> + * may still be on the orphan list. In that case, we
> + * need try remove the inode from the linked list in
> + * memory.
> + */
> + if (inode->i_nlink)
> + ext4_orphan_del(NULL, inode);
> + }
> + return ret;
> +}
> +
> #ifdef CONFIG_FS_DAX
> static ssize_t
> ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
> {
> - struct inode *inode = file_inode(iocb->ki_filp);
> + int err;
> ssize_t ret;
> + struct inode *inode = file_inode(iocb->ki_filp);
>
> if (!inode_trylock(inode)) {
> if (iocb->ki_flags & IOCB_NOWAIT)
> @@ -257,6 +308,13 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
> goto out;
>
> ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops);
> +
> + if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
> + err = ext4_handle_inode_extension(inode, iocb->ki_pos,
> + iov_iter_count(from));
> + if (err)
> + ret = err;
> + }
> out:
> inode_unlock(inode);
> if (ret > 0)
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 420fe3deed39..761ce6286b05 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3601,53 +3601,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> static int ext4_iomap_end(struct inode *inode, loff_t offset, loff_t length,
> ssize_t written, unsigned flags, struct iomap *iomap)
> {
> - int ret = 0;
> - handle_t *handle;
> - int blkbits = inode->i_blkbits;
> - bool truncate = false;
> -
> - if (!(flags & IOMAP_WRITE) || (flags & IOMAP_FAULT))
> - return 0;
> -
> - handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
> - if (IS_ERR(handle)) {
> - ret = PTR_ERR(handle);
> - goto orphan_del;
> - }
> - if (ext4_update_inode_size(inode, offset + written))
> - ext4_mark_inode_dirty(handle, inode);
> - /*
> - * We may need to truncate allocated but not written blocks beyond EOF.
> - */
> - if (iomap->offset + iomap->length >
> - ALIGN(inode->i_size, 1 << blkbits)) {
> - ext4_lblk_t written_blk, end_blk;
> -
> - written_blk = (offset + written) >> blkbits;
> - end_blk = (offset + length) >> blkbits;
> - if (written_blk < end_blk && ext4_can_truncate(inode))
> - truncate = true;
> - }
> - /*
> - * Remove inode from orphan list if we were extending a inode and
> - * everything went fine.
> - */
> - if (!truncate && inode->i_nlink &&
> - !list_empty(&EXT4_I(inode)->i_orphan))
> - ext4_orphan_del(handle, inode);
> - ext4_journal_stop(handle);
> - if (truncate) {
> - ext4_truncate_failed_write(inode);
> -orphan_del:
> - /*
> - * If truncate failed early the inode might still be on the
> - * orphan list; we need to make sure the inode is removed from
> - * the orphan list in that case.
> - */
> - if (inode->i_nlink)
> - ext4_orphan_del(NULL, inode);
> - }
> - return ret;
> + return 0;
> }
>
> const struct iomap_ops ext4_iomap_ops = {
> --
> 2.16.4
>
>
> --
> Matthew Bobrowski
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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