On Thu, 29 Aug 2019 21:22:36 -0400, Theodore Y. Ts'o wrote: > On Thu, Aug 29, 2019 at 04:53:48PM -0600, dann frazier wrote: >> JBD2: Invalid checksum recovering data block 517634 in log >> >> So is it correct to say that the checksum errors were identifying >> filesystem correctness issues, and therefore e2fsck was needed to >> correct them? > > That's correct. More precisely, checksum errors for journal blocks > are presumed to mean that file system might be corrupt, so a full > e2fsck check was needed to make sure the file system was consistent. > > > You're probably right - this issue is very easy to reproduce w/ > > data=journal,journal_checksum. I was never able to reproduce it > > otherwise. > > I've looked at the data block numbers that you've reported, and they > come from a journald file. The problem is with data=journal + > journal_checksum + mmap. Unfortunately, we don't handle that > combination correctly at the moment. > > The fix is going to have to involve fixing __ext4_journalled_writepage() > to call set_page_writeback() before it unlocks the page, adding a list of > pages under data=journalled writeback which is attached to the > transaction handle, have the jbd2 commit hook call end_page_writeback() > on all of these pages, and then in the places where ext4 calls > wait_for_stable_page() or grab_cache_page_write_begin(), > we need to add: > > if (ext4_should_journal_data(inode)) > wait_on_page_writeback(page); > If I understood and wrote things correctly, this can hit a deadlock between 1) jbd2_journal_commit_transaction() -- waiting for t_updates to drop (i.e., ext4_journal_stop() to be called), blocking commit / end_page_writeback(). and 2) ext4_write_begin() -- waiting in wait_on_page_writeback() in between the calls to ext4_journal_start()/stop(), blocking t_updates from dropping. I worked around it moving wait_on_page_writeback() before ext4_journal_start(), but wonder if this is really expected and the algorithm needs tuning/changes, or not expected and thus an implementation error. (First time with ext4 code.) P.S.: sorry to bother again about it (I already wrote/pinged on [1, 2]) but this does seem interesting and shows an issue we're interested in fixing up. Thanks again for your help/suggestions on this. [1] https://lore.kernel.org/linux-ext4/20191221202630.30718-1-mfo@xxxxxxxxxxxxx/ [2] https://lore.kernel.org/linux-ext4/20191221202630.30718-2-mfo@xxxxxxxxxxxxx/ cheers, Mauricio > It's all relatively straightforward except for the part where we have to > attach a list of pages to the currently running transaction. That > will require adding some plumbing into the jbd2 layer. > > Dann, any interest in trying to code this fix? > > - Ted
