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Date: Fri, 21 Dec 2012 17:56:50 -0800 From: Tejun Heo <tj@...nel.org> To: linux-kernel@...r.kernel.org Subject: [PATCHSET] workqueue: don't use [delayed_]work_pending() Hello, Given the current set of workqueue APIs, there are very few cases where [delayed_]work_pending() are actually necessary; however, it's seemingly somewhat popular for a few purposes including skipping queue/flush/cancel depending on the current state for optimization. work_pending() could be slightly cheaper than performing the actual operation because it can skip atomic bitops assuming that the user is synchronizing against other workqueue operations properly; however, most paths with this type of optimization are siberia-cold for this level of optimization to matter - e.g. driver detach path or parameter update via sysfs - and it's easy to get it subtly wrong and introduce difficult-to-trigger race conditions. It just isn't worth it. Other use cases include using work_pending() state to decide the state of previously scheduled async action. This too, unfortunately, seems easy to get wrong. Several users forgot that work_pending() becomes false *before* the work item starts execution and fails to synchronize with on-going execution. Unless one is specifically looking for those, they can be tricky to spot. Overall, [delayed_]work_pending() seem to bring more troubles than benefits and not using them usually results in better code. This patchset removes [delayed_]work_pending() usages from various subsystems. A lot are straight-forward removal of unnecessary optimizations. Some fix bugs around work item handling. Others restructure code so that [delayed_]work_pending() isn't necessary. After this patchset, there remain a handful of [delayed_]work_pending() users. Some of them legit. Some quite broken. Hopefully, they can be converted too and we can unexport these easy-to-misuse interface. This patchset contains the following 25 patches. 0001-charger_manager-don-t-use-delayed_-work_pending.patch 0002-ab8500_charger-don-t-use-delayed_-work_pending.patch 0003-sja1000-don-t-use-delayed_-work_pending.patch 0004-ipw2x00-simplify-scan_event-handling.patch 0005-devfreq-don-t-use-delayed_-work_pending.patch 0006-libertas-don-t-use-delayed_-work_pending.patch 0007-mwifiex-don-t-use-delayed_-work_pending.patch 0008-thinkpad_acpi-don-t-use-delayed_-work_pending.patch 0009-wl1251-don-t-use-delayed_-work_pending.patch 0010-kprobes-fix-wait_for_kprobe_optimizer.patch 0011-pm-don-t-use-delayed_-work_pending.patch 0012-bluetooth-l2cap-don-t-use-delayed_-work_pending.patch 0013-sound-wm8350-don-t-use-delayed_-work_pending.patch 0014-rfkill-don-t-use-delayed_-work_pending.patch 0015-x86-mce-don-t-use-delayed_-work_pending.patch 0016-PM-Domains-don-t-use-delayed_-work_pending.patch 0017-wm97xx-don-t-use-delayed_-work_pending.patch 0018-TMIO-MMC-don-t-use-delayed_-work_pending.patch 0019-net-caif-don-t-use-delayed_-work_pending.patch 0020-wimax-i2400m-fix-i2400m-wake_tx_skb-handling.patch 0021-tty-max3100-don-t-use-delayed_-work_pending.patch 0022-usb-at91_udc-don-t-use-delayed_-work_pending.patch 0023-video-exynos-don-t-use-delayed_-work_pending.patch 0024-debugobjects-don-t-use-delayed_-work_pending.patch 0025-ipc-don-t-use-delayed_-work_pending.patch And available in the following git branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git review-work_pending-cleanup diffstat follows. arch/x86/kernel/cpu/mcheck/mce.c | 10 ++-------- drivers/base/power/domain.c | 3 +-- drivers/devfreq/devfreq.c | 3 +-- drivers/input/touchscreen/wm97xx-core.c | 4 +--- drivers/mmc/host/tmio_mmc_pio.c | 3 +-- drivers/net/caif/caif_shmcore.c | 15 +++++---------- drivers/net/can/sja1000/peak_pci.c | 3 +-- drivers/net/wimax/i2400m/netdev.c | 31 +++++++++++++++++-------------- drivers/net/wireless/ipw2x00/ipw2100.c | 31 ++++++++----------------------- drivers/net/wireless/ipw2x00/ipw2100.h | 3 +-- drivers/net/wireless/ipw2x00/ipw2200.c | 13 +++---------- drivers/net/wireless/libertas/cfg.c | 2 +- drivers/net/wireless/libertas/if_sdio.c | 9 ++++----- drivers/net/wireless/mwifiex/sdio.c | 9 ++++----- drivers/net/wireless/ti/wl1251/ps.c | 3 +-- drivers/platform/x86/thinkpad_acpi.c | 3 +-- drivers/power/ab8500_charger.c | 13 ++++--------- drivers/power/charger-manager.c | 31 ++++++++++++++++--------------- drivers/tty/serial/max3100.c | 3 +-- drivers/usb/gadget/at91_udc.c | 3 +-- drivers/video/exynos/exynos_dp_core.c | 6 ++---- include/net/bluetooth/l2cap.h | 24 ++++++++++++++++-------- ipc/util.c | 3 +-- kernel/kprobes.c | 23 +++++++++++++++-------- kernel/power/autosleep.c | 2 +- kernel/power/qos.c | 9 +++------ lib/debugobjects.c | 7 +++---- net/bluetooth/l2cap_core.c | 7 +++---- net/rfkill/input.c | 8 +++----- sound/soc/codecs/wm8350.c | 10 ++++------ 30 files changed, 125 insertions(+), 169 deletions(-) Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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