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Date: Mon, 28 Jul 2014 14:54:43 -0700 From: Andrew Morton <akpm@...ux-foundation.org> To: Christoph Lameter <cl@...two.org> Cc: Sasha Levin <sasha.levin@...cle.com>, Gilad Ben-Yossef <gilad@...yossef.com>, Thomas Gleixner <tglx@...utronix.de>, Tejun Heo <tj@...nel.org>, John Stultz <johnstul@...ibm.com>, Mike Frysinger <vapier@...too.org>, Minchan Kim <minchan.kim@...il.com>, Hakan Akkan <hakanakkan@...il.com>, Max Krasnyansky <maxk@...lcomm.com>, Frederic Weisbecker <fweisbec@...il.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, hughd@...gle.com, viresh.kumar@...aro.org, hpa@...or.com, mingo@...nel.org, peterz@...radead.org Subject: Re: vmstat: On demand vmstat workers V8 On Mon, 28 Jul 2014 13:55:17 -0500 (CDT) Christoph Lameter <cl@...two.org> wrote: > On Fri, 25 Jul 2014, Sasha Levin wrote: > > > This patch doesn't interact well with my fuzzing setup. I'm seeing > > the following: > > > > [ 490.446927] BUG: using __this_cpu_read() in preemptible [00000000] code: kworker/16:1/7368 > > [ 490.447909] caller is __this_cpu_preempt_check+0x13/0x20 > > __this_cpu_read() from vmstat_update is only called from a kworker that > is bound to a single cpu. A false positive? schedule_delayed_work() uses system_wq. The comment in workqueue.h says * system_wq is the one used by schedule[_delayed]_work[_on](). * Multi-CPU multi-threaded. There are users which expect relatively * short queue flush time. Don't queue works which can run for too * long. but the code itself does system_wq = alloc_workqueue("events", 0, 0); ie: it didn't pass WQ_UNBOUND in the flags. Tejun, wazzup? Also, Sasha's report showed this: [ 490.464613] kernel BUG at mm/vmstat.c:1278! That's your VM_BUG_ON() in vmstat_update(). That ain't no false positive! Is this code expecting that schedule_delayed_work() will schedule the work on the current CPU? I don't think it will do that. Maybe you should be looking at schedule_delayed_work_on(). -- 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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