On Thu 08-07-21 06:45:35, Ivan Zahariev wrote: > Out of thousand machines, one would trigger the problem about every 1 to 10 > days. Some machines trigger the problem much often than others. So I can say > that we have a way to verify quickly if applying the patch will fix this for > us. > > The most important question is: Is it safe to apply the patch on production > machines with kernel 4.14? > > We can't risk data loss. And I lack the expertise to asses what risks this > small patch brings. The fix should work correctly even for older kernels. I'm not aware of any changes in this area in the past that could conflict... Honza > On 8.7.2021 г. 2:52, Theodore Ts'o wrote: > > 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 -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
