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Tejun Heo 58e814fcac btrfs: use alloc_ordered_workqueue() to create ordered workqueues 
BACKGROUND
==========

When multiple work items are queued to a workqueue, their execution order
doesn't match the queueing order. They may get executed in any order and
simultaneously. When fully serialized execution - one by one in the queueing
order - is needed, an ordered workqueue should be used which can be created
with alloc_ordered_workqueue().

However, alloc_ordered_workqueue() was a later addition. Before it, an
ordered workqueue could be obtained by creating an UNBOUND workqueue with
@max_active==1. This originally was an implementation side-effect which was
broken by 4c16bd327c ("workqueue: restore WQ_UNBOUND/max_active==1 to be
ordered"). Because there were users that depended on the ordered execution,
5c0338c687 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered")
made workqueue allocation path to implicitly promote UNBOUND workqueues w/
@max_active==1 to ordered workqueues.

While this has worked okay, overloading the UNBOUND allocation interface
this way creates other issues. It's difficult to tell whether a given
workqueue actually needs to be ordered and users that legitimately want a
min concurrency level wq unexpectedly gets an ordered one instead. With
planned UNBOUND workqueue updates to improve execution locality and more
prevalence of chiplet designs which can benefit from such improvements, this
isn't a state we wanna be in forever.

This patch series audits all call sites that create an UNBOUND workqueue w/
@max_active==1 and converts them to alloc_ordered_workqueue() as necessary.

BTRFS
=====

* fs_info->scrub_workers initialized in scrub_workers_get() was setting
  @max_active to 1 when @is_dev_replace is set and it seems that the
  workqueue actually needs to be ordered if @is_dev_replace. Update the code
  so that alloc_ordered_workqueue() is used if @is_dev_replace.

* fs_info->discard_ctl.discard_workers initialized in
  btrfs_init_workqueues() was directly using alloc_workqueue() w/
  @max_active==1. Converted to alloc_ordered_workqueue().

* fs_info->fixup_workers and fs_info->qgroup_rescan_workers initialized in
  btrfs_queue_work() use the btrfs's workqueue wrapper, btrfs_workqueue,
  which are allocated with btrfs_alloc_workqueue().

  btrfs_workqueue implements automatic @max_active adjustment which is
  disabled when the specified max limit is below a certain threshold, so
  calling btrfs_alloc_workqueue() with @limit_active==1 yields an ordered
  workqueue whose @max_active won't be changed as the auto-tuning is
  disabled.

  This is rather brittle in that nothing clearly indicates that the two
  workqueues should be ordered or btrfs_alloc_workqueue() must disable
  auto-tuning when @limit_active==1.

  This patch factors out the common btrfs_workqueue init code into
  btrfs_init_workqueue() and add explicit btrfs_alloc_ordered_workqueue().
  The two workqueues are converted to use the new ordered allocation
  interface.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: David Sterba <dsterba@suse.com>
2023-06-19 13:59:30 +02:00
arch parisc architecture fixes for kernel v6.4-rc7: 2023-06-18 09:41:39 -07:00
block blk-cgroup: Flush stats before releasing blkcg_gq 2023-06-11 19:49:29 -06:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto KEYS: asymmetric: Copy sig and digest in public_key_verify_signature() 2023-06-02 15:36:23 +02:00
Documentation RISC-V Fix for 6.4-rc7 2023-06-16 11:27:34 -07:00
drivers SCSI fixes on 20230618 2023-06-18 09:55:33 -07:00
fs btrfs: use alloc_ordered_workqueue() to create ordered workqueues 2023-06-19 13:59:30 +02:00
include ata fixes for 6.4-rc7 2023-06-18 09:48:39 -07:00
init Objtool changes for v6.4: 2023-04-28 14:02:54 -07:00
io_uring io_uring/io-wq: clear current->worker_private on exit 2023-06-14 12:54:55 -06:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel 19 hotfixes. 14 are cc:stable and the remainder address issues which were 2023-06-12 16:14:34 -07:00
lib 19 hotfixes. 14 are cc:stable and the remainder address issues which were 2023-06-12 16:14:34 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/mmap: Fix error path in do_vmi_align_munmap() 2023-06-18 09:32:17 -07:00
net dccp: Print deprecation notice. 2023-06-15 15:08:59 -07:00
rust Rust changes for v6.4 2023-04-30 11:20:22 -07:00
samples samples/bpf: Drop unnecessary fallthrough 2023-05-16 19:44:05 +02:00
scripts Locking changes in v6.4: 2023-05-05 12:56:55 -07:00
security selinux: don't use make's grouped targets feature yet 2023-06-01 13:56:13 -04:00
sound ASoC: Fixes for v6.4 2023-06-16 09:28:27 +02:00
tools Including fixes from wireless, and netfilter. 2023-06-15 21:11:17 -07:00
usr initramfs: Check negative timestamp to prevent broken cpio archive 2023-04-16 17:37:01 +09:00
virt KVM: Fix vcpu_array[0] races 2023-05-19 13:56:26 -04:00
.clang-format cxl for v6.4 2023-04-30 11:51:51 -07:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap mailmap: add entry for John Keeping 2023-06-12 11:31:52 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: sctp: move Neil to CREDITS 2023-05-12 08:51:32 +01:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Including fixes from wireless, and netfilter. 2023-06-15 21:11:17 -07:00
Makefile Linux 6.4-rc7 2023-06-18 14:06:27 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.