Revert "workqueue: make sure delayed work run in local cpu"
This reverts commit 874bbfe6. Workqueue used to implicity guarantee that work items queued without explicit CPU specified are put on the local CPU. Recent changes in timer broke the guarantee and led to vmstat breakage which was fixed by 176bed1d ("vmstat: explicitly schedule per-cpu work on the CPU we need it to run on"). vmstat is the most likely to expose the issue and it's quite possible that there are other similar problems which are a lot more difficult to trigger. As a preventive measure, 874bbfe6 ("workqueue: make sure delayed work run in local cpu") was applied to restore the local CPU guarnatee. Unfortunately, the change exposed a bug in timer code which got fixed by 22b886dd ("timers: Use proper base migration in add_timer_on()"). Due to code restructuring, the commit couldn't be backported beyond certain point and stable kernels which only had 874bbfe6 started crashing. The local CPU guarantee was accidental more than anything else and we want to get rid of it anyway. As, with the vmstat case fixed, 874bbfe6 is causing more problems than it's fixing, it has been decided to take the chance and officially break the guarantee by reverting the commit. A debug feature will be added to force foreign CPU assignment to expose cases relying on the guarantee and fixes for the individual cases will be backported to stable as necessary. Signed-off-by: Tejun Heo <email@example.com> Fixes: 874bbfe6 ("workqueue: make sure delayed work run in local cpu") Link: http://lkml.kernel.org/g/20160120211926.GJ10810@quack.suse.cz Cc: firstname.lastname@example.org Cc: Mike Galbraith <email@example.com> Cc: Henrique de Moraes Holschuh <firstname.lastname@example.org> Cc: Daniel Bilik <email@example.com> Cc: Jan Kara <firstname.lastname@example.org> Cc: Shaohua Li <email@example.com> Cc: Sasha Levin <firstname.lastname@example.org> Cc: Ben Hutchings <email@example.com> Cc: Thomas Gleixner <firstname.lastname@example.org> Cc: Daniel Bilik <email@example.com> Cc: Jiri Slaby <firstname.lastname@example.org> Cc: Michal Hocko <email@example.com>
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