51 lines
2.0 KiB
Diff
51 lines
2.0 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 11 Apr 2018 11:27:44 +0200
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Subject: [PATCH] Revert mm/vmstat.c: fix vmstat_update() preemption BUG
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.16/older/patches-4.16.7-rt1.tar.xz
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This patch reverts commit c7f26ccfb2c3 ("mm/vmstat.c: fix
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vmstat_update() preemption BUG").
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Steven saw a "using smp_processor_id() in preemptible" message and
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added a preempt_disable() section around it to keep it quiet. This is
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not the right thing to do it does not fix the real problem.
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vmstat_update() is invoked by a kworker on a specific CPU. This worker
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it bound to this CPU. The name of the worker was "kworker/1:1" so it
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should have been a worker which was bound to CPU1. A worker which can
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run on any CPU would have a `u' before the first digit.
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smp_processor_id() can be used in a preempt-enabled region as long as
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the task is bound to a single CPU which is the case here. If it could
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run on an arbitrary CPU then this is the problem we have an should seek
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to resolve.
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Not only this smp_processor_id() must not be migrated to another CPU but
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also refresh_cpu_vm_stats() which might access wrong per-CPU variables.
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Not to mention that other code relies on the fact that such a worker
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runs on one specific CPU only.
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Therefore I revert that commit and we should look instead what broke the
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affinity mask of the kworker.
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Cc: Steven J. Hill <steven.hill@cavium.com>
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Cc: Tejun Heo <htejun@gmail.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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mm/vmstat.c | 2 --
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1 file changed, 2 deletions(-)
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--- a/mm/vmstat.c
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+++ b/mm/vmstat.c
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@@ -1839,11 +1839,9 @@ static void vmstat_update(struct work_st
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* to occur in the future. Keep on running the
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* update worker thread.
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*/
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- preempt_disable();
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queue_delayed_work_on(smp_processor_id(), mm_percpu_wq,
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this_cpu_ptr(&vmstat_work),
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round_jiffies_relative(sysctl_stat_interval));
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- preempt_enable();
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}
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}
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