On Thu, Jun 10, 2021 at 07:24:37PM +0800, Zhang Yi wrote: > Current metadata buffer release logic in bdev_try_to_free_page() have > a lot of use-after-free issues when umount filesystem concurrently, and > it is difficult to fix directly because ext4 is the only user of > s_op->bdev_try_to_free_page callback and we may have to add more special > refcount or lock that is only used by ext4 into the common vfs layer, > which is unacceptable. > > One better solution is remove the bdev_try_to_free_page callback, but > the real problem is we cannot easily release journal_head on the > checkpointed buffer, so try_to_free_buffers() cannot release buffers and > page under memory pressure, which is more likely to trigger > out-of-memory. So we cannot remove the callback directly before we find > another way to release journal_head. > > This patch introduce a shrinker to free journal_head on the checkpointed > transaction. After the journal_head got freed, try_to_free_buffers() > could free buffer properly. > > Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx> > Suggested-by: Jan Kara <jack@xxxxxxx> Applied, thanks. - Ted
