Linux-Fsdevel Archive on
 help / color / Atom feed
From: Luis Chamberlain <>
	Luis Chamberlain <>
Subject: [PATCH 0/2] fs: provide a stop gap fix for buggy resume firmware API calls
Date: Fri, 16 Apr 2021 23:58:48 +0000
Message-ID: <> (raw)

Lukas has reported an issue [0] with a media driver which causes stall on
resume. At first his suspicion was that this issue was due to a bug in
btrfs. I managed to build a custom driver to reproduce the issue and
confirmed it was not a bug in btrfs. The issue is reproducible in XFS
as well. This issue is a demonstration of how broken the filesystem
suspend / resume cycle is and how easy it can be to trigger an issue.

By only doing reads with the firmware API used incorrectly, a simple
suspend / resume cycle can stall a system. The stall happens since
the hardware never gets read request issued by the filesystem as it
was already suspended. The fs waits forever. The stall also happens
because resume calls are synchronous and if one does not complete
we'll wait forever.

My new unposted VFS series for the fs freezer / resume work fixes this,
however this series will require a bit more discussion before this lands
upstream. And so this series provides a test case for the issue and an
intermediate stop-gap patch which resolves the issue for now. We can
remove this once the VFS freeze work lands upstream.


Luis Chamberlain (2):
  test_firmware: add suspend support to test buggy drivers
  fs/kernel_read_file: use usermodehelper_read_trylock() as a stop gap

 fs/kernel_read_file.c                         |  37 ++++-
 kernel/kexec_file.c                           |   9 +-
 kernel/module.c                               |   8 +-
 lib/test_firmware.c                           | 136 ++++++++++++++++--
 tools/testing/selftests/firmware/    |   8 +-
 .../selftests/firmware/      |  80 +++++++++++
 6 files changed, 261 insertions(+), 17 deletions(-)
 create mode 100755 tools/testing/selftests/firmware/


             reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 23:58 Luis Chamberlain [this message]
2021-04-16 23:58 ` [PATCH 1/2] test_firmware: add suspend support to test buggy drivers Luis Chamberlain
2021-04-21 22:23   ` Lukas Middendorf
2021-04-16 23:58 ` [PATCH 2/2] fs/kernel_read_file: use usermodehelper_read_trylock() as a stop gap Luis Chamberlain
2021-04-19 18:15   ` Luis Chamberlain
2021-04-21 20:42   ` Lukas Middendorf

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on

Archives are clonable:
	git clone --mirror linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ \
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone