From ff75d02aa0fabc7379677b7ede181acb0204c77d Mon Sep 17 00:00:00 2001
From: Jan Kara <firstname.lastname@example.org>
Date: Fri, 28 Feb 2014 09:31:10 +0100
Subject: [PATCH 2/2] ext3: Update outdated comment before
The comment is heavily outdated.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: Jan Kara <email@example.com>
fs/ext3/inode.c | 47 ++++-------------------------------------------
1 file changed, 4 insertions(+), 43 deletions(-)
@@ -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
- * 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)