>From ff75d02aa0fabc7379677b7ede181acb0204c77d Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 28 Feb 2014 09:31:10 +0100 Subject: [PATCH 2/2] ext3: Update outdated comment before ext3_ordered_writepage() The comment is heavily outdated.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: Jan Kara --- fs/ext3/inode.c | 47 ++++------------------------------------------- 1 file changed, 4 insertions(+), 43 deletions(-) diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c index 2fef98abb207..4ecf88fb69a8 100644 --- a/fs/ext3/inode.c +++ b/fs/ext3/inode.c @@ -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) -- 1.8.1.4