netdev - Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP

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Message-ID: <YzFZf0Onm6/UH7/I@dhcp22.suse.cz>
Date:   Mon, 26 Sep 2022 09:49:19 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Florian Westphal <fw@...len.de>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, vbabka@...e.cz,
        akpm@...ux-foundation.org, urezki@...il.com,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        Martin Zaharinov <micron10@...il.com>
Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC

On Fri 23-09-22 15:35:12, Florian Westphal wrote:
> Michal Hocko <mhocko@...e.com> wrote:
> > On Fri 23-09-22 12:38:58, Florian Westphal wrote:
> > > Martin Zaharinov reports BUG() in mm land for 5.19.10 kernel:
> > >  kernel BUG at mm/vmalloc.c:2437!
> > >  invalid opcode: 0000 [#1] SMP
> > >  CPU: 28 PID: 0 Comm: swapper/28 Tainted: G        W  O      5.19.9 #1
> > >  [..]
> > >  RIP: 0010:__get_vm_area_node+0x120/0x130
> > >   __vmalloc_node_range+0x96/0x1e0
> > >   kvmalloc_node+0x92/0xb0
> > >   bucket_table_alloc.isra.0+0x47/0x140
> > >   rhashtable_try_insert+0x3a4/0x440
> > >   rhashtable_insert_slow+0x1b/0x30
> > >  [..]
> > > 
> > > bucket_table_alloc uses kvzallocGPF_ATOMIC).  If kmalloc fails, this now
> > > falls through to vmalloc and hits code paths that assume GFP_KERNEL.
> > > 
> > > Revert the problematic change and stay with slab allocator.
> > 
> > Why don't you simply fix the caller?
> 
> Uh, not following?
> 
> kvzalloc(GFP_ATOMIC) was perfectly fine, is this illegal again?

kvmalloc has never really supported GFP_ATOMIC semantic.
 
> I can revert 93f976b5190df32793908d49165f78e67fcb66cf instead
> but that change is from 2018.

Yeah I would just revert this one as it relies on internal details of
kvmalloc doing or not doing a fallback.
-- 
Michal Hocko
SUSE Labs