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Sender: Tejun Heo <htejun@gmail.com>
From:   Tejun Heo <tj@kernel.org>
To:     jiangshanlai@gmail.com
Cc:     linux-kernel@vger.kernel.org, kernel-team@meta.com
Subject: [PATCHSET v2 wq/for-6.5-cleanup-ordered] workqueue: Ordered workqueue creation cleanup
Date:   Mon,  8 May 2023 15:50:19 -1000
Message-Id: <20230509015032.3768622-1-tj@kernel.org>
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Hello,

v2: Acked patches are applied to wq/for-6.5-cleanup-ordered. Some conversion
    patches were dropped (e.g. because they were using WQ_SYSFS and thus
    can't be ordered) and fixed. The final patch to remove implicit ordered
    promotion logic was broken and could trigger WARN spuriously. Fixed.

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 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be
ordered"). Because there were users that depended on the ordered execution,
5c0338c68706 ("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 callsites that create an UNBOUND workqueue w/
@max_active==1 and converts them to alloc_ordered_workqueue() as necessary
and contains the following 13 patches on top of wq/for-6.5-cleanup-ordered
branch.

 0001-scsi-ncr53c8xx-Use-default-max_active-for-hostdata-w.patch
 0002-wifi-mwifiex-Use-default-max_active-for-workqueues.patch
 0003-dm-integrity-Use-alloc_ordered_workqueue-to-create-o.patch
 0004-media-amphion-Use-alloc_ordered_workqueue-to-create-.patch
 0005-wifi-ath10-11-12k-Use-alloc_ordered_workqueue-to-cre.patch
 0006-net-wwan-t7xx-Use-alloc_ordered_workqueue-to-create-.patch
 0007-soc-qcom-qmi-Use-alloc_ordered_workqueue-to-create-o.patch
 0008-btrfs-Use-alloc_ordered_workqueue-to-create-ordered-.patch
 0009-net-qrtr-Use-alloc_ordered_workqueue-to-create-order.patch
 0010-rxrpc-Use-alloc_ordered_workqueue-to-create-ordered-.patch
 0011-crypto-octeontx2-Use-alloc_ordered_workqueue-to-crea.patch
 0012-media-coda-Use-alloc_ordered_workqueue-to-create-ord.patch
 0013-workqueue-Don-t-implicitly-make-UNBOUND-workqueues-w.patch

0001-0012 convert the existing users and 0013 drops the implicit ordered
promotion logic from alloc_workqueue(). I'll keep an eye out for a while
after merging 0022. Thankfully, these are pretty easy to grep for. The
patches can also be found in the following git branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git cleanup-ordered-v2

diffstat follows. Thanks.

 drivers/crypto/marvell/octeontx2/otx2_cptpf_main.c |   12 ++++++------
 drivers/crypto/marvell/octeontx2/otx2_cptvf_main.c |    6 +++---
 drivers/md/dm-integrity.c                          |    4 ++--
 drivers/md/dm.c                                    |    2 +-
 drivers/media/platform/amphion/vpu_core.c          |    2 +-
 drivers/media/platform/amphion/vpu_v4l2.c          |    2 +-
 drivers/media/platform/chips-media/coda-common.c   |    2 +-
 drivers/net/wireless/ath/ath10k/qmi.c              |    3 +--
 drivers/net/wireless/ath/ath11k/qmi.c              |    3 +--
 drivers/net/wireless/ath/ath12k/qmi.c              |    3 +--
 drivers/net/wireless/marvell/mwifiex/cfg80211.c    |    4 ++--
 drivers/net/wireless/marvell/mwifiex/main.c        |    8 ++++----
 drivers/net/wwan/t7xx/t7xx_hif_cldma.c             |   13 +++++++------
 drivers/net/wwan/t7xx/t7xx_hif_dpmaif_tx.c         |    5 +++--
 drivers/scsi/NCR5380.c                             |    2 +-
 drivers/soc/qcom/qmi_interface.c                   |    2 +-
 fs/btrfs/disk-io.c                                 |    2 +-
 fs/btrfs/scrub.c                                   |    6 ++++--
 include/linux/workqueue.h                          |    4 +---
 kernel/workqueue.c                                 |   23 ++++-------------------
 net/qrtr/ns.c                                      |    2 +-
 net/rxrpc/af_rxrpc.c                               |    2 +-
 22 files changed, 48 insertions(+), 64 deletions(-)