From a18b5d01819235629289212ad428a5ee2b40f0d9 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 22 Jan 2015 18:08:04 +0100 Subject: [PATCH] sched: Fix missing preemption opportunity If an interrupt fires in cond_resched(), between the call to __schedule() and the PREEMPT_ACTIVE count decrementation, and that interrupt sets TIF_NEED_RESCHED, the call to preempt_schedule_irq() will be ignored due to the PREEMPT_ACTIVE count. This kind of scenario, with irq preemption being delayed because it's interrupting a preempt-disabled area, is usually fixed up after preemption is re-enabled back with an explicit call to preempt_schedule(). This is what preempt_enable() does but a raw preempt count decrement as performed by __preempt_count_sub(PREEMPT_ACTIVE) doesn't handle delayed preemption check. Therefore when such a race happens, the rescheduling is going to be delayed until the next scheduler or preemption entrypoint. This can be a problem for scheduler latency sensitive workloads. Lets fix that by consolidating cond_resched() with preempt_schedule() internals. Reported-by: Linus Torvalds Reported-by: Ingo Molnar Original-patch-by: Ingo Molnar Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Link: http://lkml.kernel.org/r/1421946484-9298-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- Reading git-format-patch failed