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[209.85.220.65]) by mx.google.com with SMTPS id s8sor51979677wrp.36.2019.07.30.10.45.02 for (Google Transport Security); Tue, 30 Jul 2019 10:45:03 -0700 (PDT) Received-SPF: pass (google.com: domain of surenb@google.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=exjzghzO; spf=pass (google.com: domain of surenb@google.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=55SXhObGMSQ3B0w5iMjyyzalfBJzrVOBbclW7iiKCkQ=; b=exjzghzO7EhbkTlYRFfZpr6tmrtVXcAc1TUpBd+Kl4u2JUg38zLUxXExvK1XJMeAHr SlyxbTxUP2z+uLswK5N+R5aD9XurFsnLC7er31ADmEw6e+cthpO8vgTny/Txh/AaxhZy UyP5/EwXK5UjoggTiOow6IAF0r7VTqfO69BIgtbWgyUNP0ncKxhxcQKicE91n2/lV9GL ULiImcXpHVtfhBQVZL6kj0KY15jtIpMDwL5j/EdSck5lUOzB7BhcXdADbWAn7+0ox4AY clZVy+4OW2s2Mz0wdzzmFCii/R+659YbFBpBorz3TPYwfRJ6Uo8crDJGkNoDfjYysPcj PCyg== X-Google-Smtp-Source: APXvYqw7bdW2U1qAn58HfHRrUeJI5mayWPJXnuvI4caiQBk+twxM3cUV7/aucx0o+qhr7HnlZGa3XX7YY+oTszTwMDI= X-Received: by 2002:adf:e50c:: with SMTP id j12mr45502820wrm.117.1564508702443; Tue, 30 Jul 2019 10:45:02 -0700 (PDT) MIME-Version: 1.0 References: <20190730013310.162367-1-surenb@google.com> <20190730081122.GH31381@hirez.programming.kicks-ass.net> In-Reply-To: <20190730081122.GH31381@hirez.programming.kicks-ass.net> From: Suren Baghdasaryan Date: Tue, 30 Jul 2019 10:44:51 -0700 Message-ID: Subject: Re: [PATCH 1/1] psi: do not require setsched permission from the trigger creator To: Peter Zijlstra Cc: Ingo Molnar , lizefan@huawei.com, Johannes Weiner , axboe@kernel.dk, Dennis Zhou , Dennis Zhou , Andrew Morton , linux-mm , linux-doc@vger.kernel.org, LKML , kernel-team , Nick Kralevich , Thomas Gleixner Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jul 30, 2019 at 1:11 AM Peter Zijlstra wrote: > > On Mon, Jul 29, 2019 at 06:33:10PM -0700, Suren Baghdasaryan wrote: > > When a process creates a new trigger by writing into /proc/pressure/* > > files, permissions to write such a file should be used to determine whether > > the process is allowed to do so or not. Current implementation would also > > require such a process to have setsched capability. Setting of psi trigger > > thread's scheduling policy is an implementation detail and should not be > > exposed to the user level. Remove the permission check by using _nocheck > > version of the function. > > > > Suggested-by: Nick Kralevich > > Signed-off-by: Suren Baghdasaryan > > --- > > kernel/sched/psi.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > > index 7acc632c3b82..ed9a1d573cb1 100644 > > --- a/kernel/sched/psi.c > > +++ b/kernel/sched/psi.c > > @@ -1061,7 +1061,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, > > mutex_unlock(&group->trigger_lock); > > return ERR_CAST(kworker); > > } > > - sched_setscheduler(kworker->task, SCHED_FIFO, ¶m); > > + sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m); > > ARGGH, wtf is there a FIFO-99!! thread here at all !? We need psi poll_kworker to be an rt-priority thread so that psi notifications are delivered to the userspace without delay even when the CPUs are very congested. Otherwise it's easy to delay psi notifications by running a simple CPU hogger executing "chrt -f 50 dd if=/dev/zero of=/dev/null". Because these notifications are time-critical for reacting to memory shortages we can't allow for such delays. Notice that this kworker is created only if userspace creates a psi trigger. So unless you are using psi triggers you will never see this kthread created. > > kthread_init_delayed_work(&group->poll_work, > > psi_poll_work); > > rcu_assign_pointer(group->poll_kworker, kworker); > > -- > > 2.22.0.709.g102302147b-goog > > > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >