From: Vipin Sharma <vipinsh@google.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: tj@kernel.org, rdunlap@infradead.org, thomas.lendacky@amd.com,
brijesh.singh@amd.com, jon.grimm@amd.com,
eric.vantassell@amd.com, pbonzini@redhat.com, hannes@cmpxchg.org,
frankja@linux.ibm.com, borntraeger@de.ibm.com, corbet@lwn.net,
seanjc@google.com, vkuznets@redhat.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
gingell@google.com, rientjes@google.com, dionnaglaze@google.com,
kvm@vger.kernel.org, x86@kernel.org, cgroups@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [Patch v3 1/2] cgroup: sev: Add misc cgroup controller
Date: Fri, 12 Mar 2021 11:07:14 -0800 [thread overview]
Message-ID: <YEu74hkEPEyvxC85@google.com> (raw)
In-Reply-To: <YEpod5X29YqMhW/g@blackbook>
On Thu, Mar 11, 2021 at 07:59:03PM +0100, Michal Koutný wrote:
> Given different two-fold nature (SEV caller vs misc controller) of some
> remarks below, I think it makes sense to split this into two patches:
> a) generic controller implementation,
> b) hooking the controller into SEV ASIDs management.
Sounds good. I will split it.
> > + if (misc_res_capacity[type])
> > + cg->res[type].max = max;
> In theory, parallel writers can clash here, so having the limit atomic
> type to prevent this would resolve it. See also commit a713af394cf3
> ("cgroup: pids: use atomic64_t for pids->limit").
We should be fine without atomic64_t because we are using unsigned
long and not 64 bit explicitly. This will work on both 32 and 64 bit
machines.
But I will add READ_ONCE and WRITE_ONCE because of potential chances of
load tearing and store tearing.
Do you agree?
> > +static int misc_cg_capacity_show(struct seq_file *sf, void *v)
> > +{
> > + int i;
> > + unsigned long cap;
> > +
> > + for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> > + cap = READ_ONCE(misc_res_capacity[i]);
> Why is READ_ONCE only here and not in other places that (actually) check
> against the set capacity value? Also, there should be a paired
> WRITE_ONCCE in misc_cg_set_capacity().
This was only here to avoid multiple reads of capacity and making sure
if condition and seq_print will see the same value. Also, I was not
aware of load and store tearing of properly aligned and machine word
size variables. I will add READ_ONCE and WRITE_ONCE at
other places.
Thanks
Vipin
next prev parent reply other threads:[~2021-03-12 19:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 23:19 [Patch v3 0/2] cgroup: New misc cgroup controller Vipin Sharma
2021-03-04 23:19 ` [Patch v3 1/2] cgroup: sev: Add " Vipin Sharma
2021-03-11 18:59 ` Michal Koutný
2021-03-12 19:07 ` Vipin Sharma [this message]
2021-03-15 18:34 ` Michal Koutný
2021-03-12 19:48 ` Vipin Sharma
2021-03-12 20:51 ` Sean Christopherson
2021-03-12 21:18 ` Tom Lendacky
2021-03-19 21:28 ` Jacob Pan
2021-03-22 18:54 ` Vipin Sharma
2021-03-24 16:17 ` Jacob Pan
2021-03-24 22:09 ` Vipin Sharma
2021-03-04 23:19 ` [Patch v3 2/2] cgroup: sev: Miscellaneous cgroup documentation Vipin Sharma
2021-03-07 12:48 ` [Patch v3 0/2] cgroup: New misc cgroup controller Tejun Heo
2021-03-11 18:58 ` Michal Koutný
2021-03-11 19:39 ` Tejun Heo
2021-03-12 17:49 ` Vipin Sharma
2021-03-15 19:10 ` Michal Koutný
2021-03-22 18:24 ` Vipin Sharma
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