On Wed, Feb 28, 2024 at 02:47:26PM -0500, Brian Foster wrote:
> Hi Kent,
>
> Firstly, I confirmed that today's master seems to avoid the splat I sent
> previously (re: your comment about a reverse journal replay patch or
> some such).
>
> I still reproduce the stall issue on this system. After peeling away at
> it, I was eventually able to reproduce without the drop writes
> (dm-flakey) behavior from the test, and with fio using either the libaio
> or sync I/O engine options. The sync I/O mode fortunately provides a
> more useful stack trace:
>
> # cat /proc/177747/stack
> [<0>] bch2_dio_write_flush+0x122/0x160 [bcachefs]
> [<0>] bch2_direct_write+0xb53/0xce0 [bcachefs]
> [<0>] bch2_write_iter+0x142/0xc70 [bcachefs]
> [<0>] vfs_write+0x29b/0x470
> [<0>] ksys_write+0x6f/0xf0
> [<0>] do_syscall_64+0x86/0x170
> [<0>] entry_SYSCALL_64_after_hwframe+0x6e/0x76
>
> ... which resolves down to the closure_sync() call in
> bch2_dio_write_flush(). The problem seems to go away if I remove the
> preceding journal flush from that function. This seems to rule out
> io_uring/aio and instead suggest that we're getting stuck somehow
> waiting on a journal flush.
>
> Based on that I went back to the first commit before 746a33c96b7a0
> ("bcachefs: better journal pipelining"). With that, I can run hundreds
> of iterations of generic/703 without a problem, so this appears to be a
> regression associated with the journal pipeline improvements. I'm
> currently re-running on the last known good commit with my test tweaks
> backed out (i.e. so back to io_uring and drop writes) just to
> corroborate that it's the same problem, but so far it's running as
> expected...
So I suppose the journal must be getting stuck, and a journal write
isn't completing - what does sysfs internal/journal_debug say when it happens?
