linux/drivers/xen
Tejun Heo 715557b02c xen/pvcalls: 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 callsites that create an UNBOUND workqueue w/
@max_active==1 and converts them to alloc_ordered_workqueue() as necessary.

WHAT TO LOOK FOR
================

The conversions are from

  alloc_workqueue(WQ_UNBOUND | flags, 1, args..)

to 

  alloc_ordered_workqueue(flags, args...)

which don't cause any functional changes. If you know that fully ordered
execution is not ncessary, please let me know. I'll drop the conversion and
instead add a comment noting the fact to reduce confusion while conversion
is in progress.

If you aren't fully sure, it's completely fine to let the conversion
through. The behavior will stay exactly the same and we can always
reconsider later.

As there are follow-up workqueue core changes, I'd really appreciate if the
patch can be routed through the workqueue tree w/ your acks. Thanks.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: xen-devel@lists.xenproject.org
2023-05-08 15:33:12 -10:00
..
events xen: Allow platform PCI interrupt to be shared 2023-02-13 06:53:20 +01:00
xen-pciback xen/pciback: don't call pcistub_device_put() under lock 2023-04-24 07:27:10 +02:00
xenbus driver core: make struct bus_type.uevent() take a const * 2023-01-27 13:45:52 +01:00
xenfs xen: remove unnecessary (void*) conversions 2023-03-16 12:04:00 +01:00
acpi.c
arm-device.c
balloon.c xen: simplify sysctl registration for balloon 2023-04-13 11:49:20 -07:00
biomerge.c
cpu_hotplug.c
dbgp.c
efi.c efi: Apply allowlist to EFI configuration tables when running under Xen 2023-01-23 11:33:24 +01:00
evtchn.c
features.c x86/xen: Remove undefined behavior in setup_features() 2022-06-21 16:36:11 +02:00
gntalloc.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
gntdev-common.h xen/gntdev: Accommodate VMA splitting 2022-10-06 10:40:21 +02:00
gntdev-dmabuf.c xen/gntdev: Prepare to dynamic dma-buf locking specification 2022-10-18 01:21:47 +03:00
gntdev-dmabuf.h
gntdev.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
grant-dma-iommu.c xen/grant-dma-iommu: Implement a dummy probe_device() callback 2023-02-13 07:22:08 +01:00
grant-dma-ops.c xen/virtio: Handle PCI devices which Host controller is described in DT 2022-12-05 12:59:49 +01:00
grant-table.c xen/grants: prevent integer overflow in gnttab_dma_alloc_pages() 2022-09-02 11:05:19 +02:00
Kconfig xen: Kconfig: Fix spelling mistake "Maxmium" -> "Maximum" 2022-10-12 08:39:50 +02:00
Makefile xen/grant-dma-iommu: Introduce stub IOMMU driver 2022-06-06 16:07:30 +02:00
manage.c xen/manage: Use orderly_reboot() to reboot 2022-08-01 07:42:22 +02:00
mcelog.c
mem-reservation.c
pci.c xen/pci: Make use of the helper macro LIST_HEAD() 2022-02-10 11:10:23 +01:00
pcpu.c ACPI: processor: Fix evaluating _PDC method when running as Xen dom0 2023-03-22 19:36:31 +01:00
platform-pci.c xen: Allow platform PCI interrupt to be shared 2023-02-13 06:53:20 +01:00
privcmd-buf.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
privcmd.c mm: replace vma->vm_flags direct modifications with modifier calls 2023-02-09 16:51:39 -08:00
privcmd.h
pvcalls-back.c xen/pvcalls: Use alloc_ordered_workqueue() to create ordered workqueues 2023-05-08 15:33:12 -10:00
pvcalls-front.c xen/pvcalls: don't call bind_evtchn_to_irqhandler() under lock 2023-04-24 07:27:10 +02:00
pvcalls-front.h
swiotlb-xen.c swiotlb-xen: fix DMA_ATTR_NO_KERNEL_MAPPING on arm 2022-05-11 19:48:32 +02:00
sys-hypervisor.c xen: sysfs: make kobj_type structure constant 2023-02-18 16:50:21 +01:00
time.c
unpopulated-alloc.c xen/balloon: don't use PV mode extra memory for zone device allocations 2022-04-07 15:08:37 -05:00
xen-acpi-pad.c ACPI: make remove callback of ACPI driver void 2022-11-23 19:11:22 +01:00
xen-acpi-processor.c
xen-balloon.c
xen-front-pgdir-shbuf.c xen: Replace one-element array with flexible-array member 2023-02-13 09:15:45 +01:00
xen-scsiback.c xen: branch for v6.4-rc1 2023-04-27 17:27:06 -07:00
xlate_mmu.c xen: unexport __init-annotated xen_xlate_map_ballooned_pages() 2022-06-07 08:11:35 +02:00