linux-kernel - [PATCH 0/5] bcachefs async object debugging

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Message-ID: <20250421172607.1781982-1-kent.overstreet@linux.dev>
Date: Mon, 21 Apr 2025 13:26:00 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: linux-bcachefs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Subject: [PATCH 0/5] bcachefs async object debugging

More debugging infrastructure that might perhaps be of wider interest.

Currently, when an asynchronous op gets stuck and never completes, it's
a real problem to debug: all our normal introspection (e.g.
/proc/pid/stack) doesn't work.

e.g. if a bio doesn't (seem to) complete - what happened to it?
Difficult question to answer. We have giant state machines, and
debugging issues where we stop making forward progress requires
visibility into the whole thing.

(basic question: did the bio complete and the endio not funtion not flip
the correct state bit, or did it get lost?)

In the reports/test failures I look at, I've been seeing these the most
in or at the boundary of mm - compaction/migration, writeback...

This series introduces infrastructure that'll allow us to debug these
kinds of issues in production:

- fast_list, which is a high-enough performance "list" to track these
  kinds of objects (radix tree + percpu buffer)

- infrastructure for making them visible in debugfs, hooking them up to
  pretty printers

- and the last patch hooks into just some of the bcachefs paths where
  we we need this

Kent Overstreet (5):
  bcachefs: bch2_bio_to_text()
  bcachefs: bch2_read_bio_to_text
  bcachefs: fast_list
  bcachefs: Async object debugging
  bcachefs: Make various async objs visible in debugfs

 fs/bcachefs/Kconfig            |   5 ++
 fs/bcachefs/Makefile           |   3 +
 fs/bcachefs/async_objs.c       | 126 +++++++++++++++++++++++++++++
 fs/bcachefs/async_objs.h       |  39 +++++++++
 fs/bcachefs/async_objs_types.h |  24 ++++++
 fs/bcachefs/bcachefs.h         |   7 ++
 fs/bcachefs/btree_io.c         |  12 +++
 fs/bcachefs/btree_io.h         |   8 ++
 fs/bcachefs/data_update.c      |  18 ++++-
 fs/bcachefs/data_update.h      |  15 ++++
 fs/bcachefs/debug.c            |  52 +++++-------
 fs/bcachefs/debug.h            |  18 +++++
 fs/bcachefs/errcode.h          |   1 +
 fs/bcachefs/fast_list.c        | 140 +++++++++++++++++++++++++++++++++
 fs/bcachefs/fast_list.h        |  41 ++++++++++
 fs/bcachefs/io_read.c          |  76 +++++++++++++++---
 fs/bcachefs/io_read.h          |  14 ++++
 fs/bcachefs/super.c            |   3 +
 fs/bcachefs/util.c             |  10 +++
 fs/bcachefs/util.h             |   2 +
 20 files changed, 566 insertions(+), 48 deletions(-)
 create mode 100644 fs/bcachefs/async_objs.c
 create mode 100644 fs/bcachefs/async_objs.h
 create mode 100644 fs/bcachefs/async_objs_types.h
 create mode 100644 fs/bcachefs/fast_list.c
 create mode 100644 fs/bcachefs/fast_list.h

-- 
2.49.0