stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock
[ Upstream commit 0b26351b ] Matt reported the following deadlock: CPU0 CPU1 schedule(.prev=migrate/0) <fault> pick_next_task() ... idle_balance() migrate_swap() active_balance() stop_two_cpus() spin_lock(stopper0->lock) spin_lock(stopper1->lock) ttwu(migrate/0) smp_cond_load_acquire() -- waits for schedule() stop_one_cpu(1) spin_lock(stopper1->lock) -- waits for stopper lock Fix this deadlock by taking the wakeups out from under stopper->lock. This allows the active_balance() to queue the stop work and finish the context switch, which in turn allows the wakeup from migrate_swap() to observe the context and complete the wakeup. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reported-by: Matt Fleming <matt@codeblueprint.co.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Matt Fleming <matt@codeblueprint.co.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Galbraith <umgwanakikbuti@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20180420095005.GH4064@hirez.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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