On Wed, Jul 07, 2021 at 09:42:25PM +0300, Ivan Zahariev wrote: > Hello, > > We're running Linux kernel 4.14.x and our systems occasionally suffer a bug > which is already fixed: https://github.com/torvalds/linux/commit/53cf978457325d8fb2cdecd7981b31a8229e446e > > This bugfix hasn't been ported to Linux kernels 4.14 or 4.19. The patch > applies cleanly. The two files "fs/jbd2/checkpoint.c" and > "fs/jbd2/journal.c" seem pretty identical in the affected sections compared > to kernel 5.4 where we have this bugfix already applied. > > Is it on purpose that this bugfix hasn't been ported to 4.14? Is it safe > that we backport it manually in our kernel 4.14 builds? Or is the "ext4" > system in 4.14 and 5.4 fundamentally different and this would lead to data > loss or other problems? The commit was over two years ago, so my memory is not going to be perfect. However, Jan had made a comment suggesting the approach in this commit because it should be easier to backport into older stble kernels[1]. "Since proper locking change is going to be a bit more involved, can you perhaps fix this deadlock by just dropping j_checkpoint_mutex in log_do_checkpoint() when we are going to wait for transaction commit. I've checked and that should be fine and that is going to be much easier change to backport into stable kernels..." [1] https://marc.info/?l=linux-ext4&m=154212553014669&w=2 So I suspect it was just that I failed to remember to add a "Cc: stable@xxxxxxxxxx" and so it was never automatically backported into 4.14 or 4.19. Do you have a reliable reproduction which is triggering the deadlock on your kernels? If so, have you tried applying the patch and does it make the problem go away for you? Cheers, - Ted
