linux-kernel - Re: WARNING in kvmalloc

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Message-ID: <20180214115119.GA3443@dhcp22.suse.cz>
Date:   Wed, 14 Feb 2018 12:51:19 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Matthew Wilcox <willy@...radead.org>,
        syzbot <syzbot+1a240cdb1f4cc88819df@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, dhowells@...hat.com, hannes@...xchg.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, mingo@...nel.org,
        rppt@...ux.vnet.ibm.com, syzkaller-bugs@...glegroups.com,
        vbabka@...e.cz, viro@...iv.linux.org.uk,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        brouer@...hat.com, "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: WARNING in kvmalloc_node

On Wed 14-02-18 19:47:30, Jason Wang wrote:
> 
> 
> On 2018年02月14日 17:28, Daniel Borkmann wrote:
> > [ +Jason, +Jesper ]
> > 
> > On 02/14/2018 09:43 AM, Michal Hocko wrote:
> > > On Tue 13-02-18 18:55:33, Matthew Wilcox wrote:
> > > > On Tue, Feb 13, 2018 at 03:59:01PM -0800, syzbot wrote:
> > > [...]
> > > > >   kvmalloc include/linux/mm.h:541 [inline]
> > > > >   kvmalloc_array include/linux/mm.h:557 [inline]
> > > > >   __ptr_ring_init_queue_alloc include/linux/ptr_ring.h:474 [inline]
> > > > >   ptr_ring_init include/linux/ptr_ring.h:492 [inline]
> > > > >   __cpu_map_entry_alloc kernel/bpf/cpumap.c:359 [inline]
> > > > >   cpu_map_update_elem+0x3c3/0x8e0 kernel/bpf/cpumap.c:490
> > > > >   map_update_elem kernel/bpf/syscall.c:698 [inline]
> > > > Blame the BPF people, not the MM people ;-)
> > Heh, not really. ;-)
> > 
> > > Yes. kvmalloc (the vmalloc part) doesn't support GFP_ATOMIC semantic.
> > Agree, that doesn't work.
> > 
> > Bug was added in commit 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails").
> > 
> > Jason, please take a look at fixing this, thanks!
> 
> It looks to me the only solution is to revert that commit.

Do you really need this to be GFP_ATOMIC? I can see some callers are
under RCU read lock but can we perhaps do the allocation outside of this
section?
-- 
Michal Hocko
SUSE Labs