linux-kernel - Re: EBPF-triggered WARNING at mm/percpu.c:1361 in v4-14-rc2

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Message-ID: <20170928145302.GE15129@devbig577.frc2.facebook.com>
Date:   Thu, 28 Sep 2017 07:53:02 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        netdev@...r.kernel.org, syzkaller@...glegroups.com,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: EBPF-triggered WARNING at mm/percpu.c:1361 in v4-14-rc2

Hello,

On Thu, Sep 28, 2017 at 03:45:38PM +0100, Mark Rutland wrote:
> > Perhaps the pr_warn() should be ratelimited; or could there be an
> > option where we only return NULL, not triggering a warn at all (which
> > would likely be what callers might do anyway when checking against
> > PCPU_MIN_UNIT_SIZE and then bailing out)?
> 
> Those both make sense to me; checking __GFP_NOWARN should be easy
> enough.

That also makes sense.

> Just to check, do you think that dev_map_alloc() should explicitly test
> the size against PCPU_MIN_UNIT_SIZE, prior to calling pcpu_alloc()?

But let's please not do this.

Thanks.

-- 
tejun