> > On Wed 07-05-14 14:15:24, Namjae Jeon wrote: > > When we perform a data integrity sync we tag all the dirty pages with > > PAGECACHE_TAG_TOWRITE at start of ext4_da_writepages. > > Later we check for this tag in write_cache_pages_da and creates a > > struct mpage_da_data containing contiguously indexed pages tagged with this > > tag and sync these pages with a call to mpage_da_map_and_submit. > > This process is done in while loop until all the PAGECACHE_TAG_TOWRITE pages > > are synced. We also do journal start and stop in each iteration. > > journal_stop could initiate journal commit which would call ext4_writepage > > which in turn will call ext4_bio_write_page even for delayed OR unwritten > > buffers. When ext4_bio_write_page is called for such buffers, even though it > > does not sync them but it clears the PAGECACHE_TAG_TOWRITE of the corresponding > > page and hence these pages are also not synced by the currently running data > > integrity sync. We will end up with dirty pages although sync is completed. > > > > This could cause a potential data loss when the sync call is followed by a > > truncate_pagecache call, which is exactly the case in collapse_range. > > (It will cause generic/127 failure in xfstests) > > > > To avoid this issue, we can use set_page_writeback_keepwrite instead of > > set_page_writeback, which doesn't clear TOWRITE tag. > > > > Cc: Jan Kara <jack@xxxxxxx> > > Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx> > > Signed-off-by: Ashish Sangwan <a.sangwan@xxxxxxxxxxx> > The patch looks good. You can add: > Reviewed-by: Jan Kara <jack@xxxxxxx> > > BTW you should also cc linux-mm@xxxxxxxxx with this patch since it touches > the mm code. Okay. Thanks for your review! > > Honza -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
