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Date: Mon, 2 Jun 2008 11:31:06 +0200
From: Jan Kara <jack@...e.cz>
To: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: cmm@...ibm.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Add validation to jbd lock inversion patch and
split and writepage
Hi Aneesh,
Thanks for the patch but I though we decided to do this a bit differently -
see below.
On Fri 30-05-08 19:09:27, Aneesh Kumar K.V wrote:
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
> fs/ext4/inode.c | 181 +++++++++++++++++++++++++++++++++++++++++++++++--------
> 1 files changed, 156 insertions(+), 25 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index a96c325..b122425 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1479,6 +1479,11 @@ static int jbd2_journal_dirty_data_fn(handle_t *handle, struct buffer_head *bh)
> return 0;
> }
>
> +static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
> +{
> + return (!buffer_mapped(bh) || buffer_delay(bh));
> +}
> +
> /*
> * Note that we don't need to start a transaction unless we're journaling
> * data because we should have holes filled from ext4_page_mkwrite(). If
> @@ -1531,18 +1536,26 @@ static int jbd2_journal_dirty_data_fn(handle_t *handle, struct buffer_head *bh)
> static int __ext4_ordered_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> - struct inode *inode = page->mapping->host;
> - struct buffer_head *page_bufs;
> + int ret = 0, err;
> + unsigned long len;
> handle_t *handle = NULL;
> - int ret = 0;
> - int err;
> + struct buffer_head *page_bufs;
> + struct inode *inode = page->mapping->host;
> + loff_t size = i_size_read(inode);
>
> - if (!page_has_buffers(page)) {
> - create_empty_buffers(page, inode->i_sb->s_blocksize,
> - (1 << BH_Dirty)|(1 << BH_Uptodate));
> - }
This is OK.
> page_bufs = page_buffers(page);
> - walk_page_buffers(handle, page_bufs, 0,
> + if (page->index == size >> PAGE_CACHE_SHIFT)
> + len = size & ~PAGE_CACHE_MASK;
> + else
> + len = PAGE_CACHE_SIZE;
> +
> + if (walk_page_buffers(NULL, page_bufs, 0,
> + len, NULL, ext4_bh_unmapped_or_delay)) {
> + printk(KERN_CRIT "%s called with unmapped or delay buffer\n",
> + __func__);
> + BUG();
> + }
But I'd move this check to ext4_ordered_writepage().
> + walk_page_buffers(NULL, page_bufs, 0,
> PAGE_CACHE_SIZE, NULL, bget_one);
>
> ret = block_write_full_page(page, ext4_get_block, wbc);
> @@ -1574,8 +1587,8 @@ static int __ext4_ordered_writepage(struct page *page,
> ret = err;
> }
> out_put:
> - walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE, NULL,
> - bput_one);
> + walk_page_buffers(handle, page_bufs, 0,
> + PAGE_CACHE_SIZE, NULL, bput_one);
> return ret;
> }
>
> @@ -1583,7 +1596,7 @@ static int ext4_ordered_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> J_ASSERT(PageLocked(page));
> -
> + BUG_ON(!page_has_buffers(page));
> /*
> * We give up here if we're reentered, because it might be for a
> * different filesystem.
> @@ -1599,18 +1612,34 @@ static int ext4_ordered_writepage(struct page *page,
> static int __ext4_writeback_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> + unsigned long len;
> + struct buffer_head *page_bufs;
> struct inode *inode = page->mapping->host;
> + loff_t size = i_size_read(inode);
> +
> + page_bufs = page_buffers(page);
> + if (page->index == size >> PAGE_CACHE_SHIFT)
> + len = size & ~PAGE_CACHE_MASK;
> + else
> + len = PAGE_CACHE_SIZE;
>
> + if (walk_page_buffers(NULL, page_bufs, 0,
> + len, NULL, ext4_bh_unmapped_or_delay)) {
> + printk(KERN_CRIT "%s called with unmapped or delay buffer\n",
> + __func__);
> + BUG();
> + }
And similarly move this check to ext4_writeback_writepage().
> if (test_opt(inode->i_sb, NOBH))
> return nobh_writepage(page, ext4_get_block, wbc);
> else
> return block_write_full_page(page, ext4_get_block, wbc);
> }
>
> -
> static int ext4_writeback_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> + BUG_ON(!page_has_buffers(page));
> +
> if (!ext4_journal_current_handle())
> return __ext4_writeback_writepage(page, wbc);
>
> @@ -1622,18 +1651,31 @@ static int ext4_writeback_writepage(struct page *page,
> static int __ext4_journalled_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> + int ret = 0, err;
> + unsigned long len;
> + handle_t *handle = NULL;
> struct address_space *mapping = page->mapping;
> struct inode *inode = mapping->host;
> struct buffer_head *page_bufs;
> - handle_t *handle = NULL;
> - int ret = 0;
> - int err;
> + loff_t size = i_size_read(inode);
> +
> + page_bufs = page_buffers(page);
> + if (page->index == size >> PAGE_CACHE_SHIFT)
> + len = size & ~PAGE_CACHE_MASK;
> + else
> + len = PAGE_CACHE_SIZE;
>
> + if (walk_page_buffers(NULL, page_bufs, 0,
> + len, NULL, ext4_bh_unmapped_or_delay)) {
> + printk(KERN_CRIT "%s called with unmapped or delay buffer\n",
> + __func__);
> + BUG();
> + }
> + /* FIXME!! do we need to call prepare_write for a mapped buffer */
This can go to ext4_journalled_writepage(). What is actually this FIXME
about? I'm not sure I get it...
> ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE, ext4_get_block);
> if (ret != 0)
> goto out_unlock;
>
> - page_bufs = page_buffers(page);
> walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE, NULL,
> bget_one);
> /* As soon as we unlock the page, it can go away, but we have
> @@ -1671,14 +1713,13 @@ static int __ext4_journalled_writepage(struct page *page,
> static int ext4_journalled_writepage(struct page *page,
> struct writeback_control *wbc)
> {
> + BUG_ON(!page_has_buffers(page));
> +
> if (ext4_journal_current_handle())
> goto no_write;
>
> - if (!page_has_buffers(page) || PageChecked(page)) {
> - /*
> - * It's mmapped pagecache. Add buffers and journal it. There
> - * doesn't seem much point in redirtying the page here.
> - */
> + if (PageChecked(page)) {
> + /* dirty pages in data=journal mode */
> ClearPageChecked(page);
> return __ext4_journalled_writepage(page, wbc);
> } else {
> @@ -3520,6 +3561,96 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
> return err;
> }
>
> +static int __ext4_journalled_allocpage(struct page *page,
> + struct writeback_control *wbc)
> +{
> + int ret = 0, err;
> + handle_t *handle = NULL;
> + struct address_space *mapping = page->mapping;
> + struct inode *inode = mapping->host;
> + struct buffer_head *page_bufs;
> +
> + /* if alloc we are called after statring a journal */
> + handle = ext4_journal_current_handle();
> + BUG_ON(!handle);
> +
> + ret = block_prepare_write(page, 0, PAGE_CACHE_SIZE, ext4_get_block);
> + if (ret != 0)
> + goto out_unlock;
> +
> + /* FIXME!! should we do a bget_one */
> + page_bufs = page_buffers(page);
> + ret = walk_page_buffers(handle, page_bufs, 0,
> + PAGE_CACHE_SIZE, NULL, do_journal_get_write_access);
> +
> + err = walk_page_buffers(handle, page_bufs, 0,
> + PAGE_CACHE_SIZE, NULL, write_end_fn);
> + if (ret == 0)
> + ret = err;
> + EXT4_I(inode)->i_state |= EXT4_STATE_JDATA;
> +
> +out_unlock:
> + unlock_page(page);
> + return ret;
> +}
> +
> +static int __ext4_ordered_allocpage(struct page *page,
> + struct writeback_control *wbc)
> +{
> + int ret = 0;
> + handle_t *handle = NULL;
> + struct buffer_head *page_bufs;
> + struct inode *inode = page->mapping->host;
> +
> + /* if alloc we are called after statring a journal */
> + handle = ext4_journal_current_handle();
> + BUG_ON(!handle);
> + if (!page_has_buffers(page)) {
> + create_empty_buffers(page, inode->i_sb->s_blocksize,
> + (1 << BH_Dirty)|(1 << BH_Uptodate));
> + }
> + page_bufs = page_buffers(page);
> + walk_page_buffers(handle, page_bufs, 0,
> + PAGE_CACHE_SIZE, NULL, bget_one);
> +
> + ret = block_write_full_page(page, ext4_get_block, wbc);
> +
> + /*
> + * The page can become unlocked at any point now, and
> + * truncate can then come in and change things. So we
> + * can't touch *page from now on. But *page_bufs is
> + * safe due to elevated refcount.
> + */
> +
> + /*
> + * And attach them to the current transaction. But only if
> + * block_write_full_page() succeeded. Otherwise they are unmapped,
> + * and generally junk.
> + */
> + if (ret == 0) {
> + ret = walk_page_buffers(handle, page_bufs, 0, PAGE_CACHE_SIZE,
> + NULL, jbd2_journal_dirty_data_fn);
> + }
> + walk_page_buffers(handle, page_bufs, 0,
> + PAGE_CACHE_SIZE, NULL, bput_one);
> + return ret;
> +}
> +
> +static int __ext4_writeback_allocpage(struct page *page,
> + struct writeback_control *wbc)
> +{
> + handle_t *handle = NULL;
> + struct inode *inode = page->mapping->host;
> + /* if alloc we are called after statring a journal */
> + handle = ext4_journal_current_handle();
> + BUG_ON(!handle);
> +
> + if (test_opt(inode->i_sb, NOBH))
> + return nobh_writepage(page, ext4_get_block, wbc);
> + else
> + return block_write_full_page(page, ext4_get_block, wbc);
> +}
> +
And then you don't need these __ext4_..._allocpage() calls because that
is what's left in __ext4_..._writepage(), isn't it? It seems also logically
more consistent - you do checks in ext4_..._writepage() and then you do the
real work in __ext4_..._writepage().
For data=journaled mode, it may be better to really have
ext4_journaled_allocpage() because we don't have to do nasty locking
tricks. But for writeback and ordered mode I really see no need for these
special functions. So at least for these two, I'd change the code as I
suggest.
> static int ext4_bh_prepare_fill(handle_t *handle, struct buffer_head *bh)
> {
> if (!buffer_mapped(bh)) {
> @@ -3596,11 +3727,11 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> wbc.range_start = page_offset(page);
> wbc.range_end = page_offset(page) + len;
> if (ext4_should_writeback_data(inode))
> - ret = __ext4_writeback_writepage(page, &wbc);
> + ret = __ext4_writeback_allocpage(page, &wbc);
> else if (ext4_should_order_data(inode))
> - ret = __ext4_ordered_writepage(page, &wbc);
> + ret = __ext4_ordered_allocpage(page, &wbc);
> else
> - ret = __ext4_journalled_writepage(page, &wbc);
> + ret = __ext4_journalled_allocpage(page, &wbc);
> /* Page got unlocked in writepage */
> err = ext4_journal_stop(handle);
> if (!ret)
> --
> 1.5.5.1.357.g1af8b.dirty
Honza
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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