diff options
Diffstat (limited to 'fs/ext4')
| -rw-r--r-- | fs/ext4/inode.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 074aeba78259..657a98fa80b6 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2124,15 +2124,29 @@ static int ext4_writepage(struct page *page, static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page) { int len; - loff_t size = i_size_read(mpd->inode); + loff_t size; int err; BUG_ON(page->index != mpd->first_page); + clear_page_dirty_for_io(page); + /* + * We have to be very careful here! Nothing protects writeback path + * against i_size changes and the page can be writeably mapped into + * page tables. So an application can be growing i_size and writing + * data through mmap while writeback runs. clear_page_dirty_for_io() + * write-protects our page in page tables and the page cannot get + * written to again until we release page lock. So only after + * clear_page_dirty_for_io() we are safe to sample i_size for + * ext4_bio_write_page() to zero-out tail of the written page. We rely + * on the barrier provided by TestClearPageDirty in + * clear_page_dirty_for_io() to make sure i_size is really sampled only + * after page tables are updated. + */ + size = i_size_read(mpd->inode); if (page->index == size >> PAGE_SHIFT) len = size & ~PAGE_MASK; else len = PAGE_SIZE; - clear_page_dirty_for_io(page); err = ext4_bio_write_page(&mpd->io_submit, page, len, mpd->wbc, false); if (!err) mpd->wbc->nr_to_write--; |