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Commit d680104f authored by Jan Kara's avatar Jan Kara
Browse files

ext3: Update outdated comment before ext3_ordered_writepage() 



The comment is heavily outdated. The recursion into the filesystem isn't
possible because we use GFP_NOFS for our allocations, the issue about
block_write_full_page() dirtying tail page is long resolved as well
(that function doesn't dirty buffers at all), and finally we don't start
a transaction if all blocks are already allocated and mapped.

Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 99128add

fs/ext3/inode.c

+4 −43
Original line number Diff line number Diff line
@@ -1559,56 +1559,17 @@ static int buffer_unmapped(handle_t *handle, struct buffer_head *bh) 
}



/*

 * Note that we always start a transaction even if we're not journalling

 * data.  This is to preserve ordering: any hole instantiation within

 * __block_write_full_page -> ext3_get_block() should be journalled

 * along with the data so we don't crash and then get metadata which

 * Note that whenever we need to map blocks we start a transaction even if

 * we're not journalling data.  This is to preserve ordering: any hole

 * instantiation within __block_write_full_page -> ext3_get_block() should be

 * journalled along with the data so we don't crash and then get metadata which

 * refers to old data.

 *

 * In all journalling modes block_write_full_page() will start the I/O.

 *

 * Problem:

 *

 *	ext3_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->

 *		ext3_writepage()

 *

 * Similar for:

 *

 *	ext3_file_write() -> generic_file_write() -> __alloc_pages() -> ...

 *

 * Same applies to ext3_get_block().  We will deadlock on various things like

 * lock_journal and i_truncate_mutex.

 *

 * Setting PF_MEMALLOC here doesn't work - too many internal memory

 * allocations fail.

 *

 * 16May01: If we're reentered then journal_current_handle() will be

 *	    non-zero. We simply *return*.

 *

 * 1 July 2001: @@@ FIXME:

 *   In journalled data mode, a data buffer may be metadata against the

 *   current transaction.  But the same file is part of a shared mapping

 *   and someone does a writepage() on it.

 *

 *   We will move the buffer onto the async_data list, but *after* it has

 *   been dirtied. So there's a small window where we have dirty data on

 *   BJ_Metadata.

 *

 *   Note that this only applies to the last partial page in the file.  The

 *   bit which block_write_full_page() uses prepare/commit for.  (That's

 *   broken code anyway: it's wrong for msync()).

 *

 *   It's a rare case: affects the final partial page, for journalled data

 *   where the file is subject to bith write() and writepage() in the same

 *   transction.  To fix it we'll need a custom block_write_full_page().

 *   We'll probably need that anyway for journalling writepage() output.

 *

 * We don't honour synchronous mounts for writepage().  That would be

 * disastrous.  Any write() or metadata operation will sync the fs for

 * us.

 *

 * AKPM2: if all the page's buffers are mapped to disk and !data=journal,

 * we don't need to open a transaction here.

 */

static int ext3_ordered_writepage(struct page *page,

				struct writeback_control *wbc)