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Date:   Mon, 26 Sep 2022 09:49:19 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Florian Westphal <fw@strlen.de>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org, vbabka@suse.cz,
        akpm@linux-foundation.org, urezki@gmail.com,
        netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
        Martin Zaharinov <micron10@gmail.com>
Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC
Message-ID: <YzFZf0Onm6/UH7/I@dhcp22.suse.cz>
References: <20220923103858.26729-1-fw@strlen.de>
 <Yy20toVrIktiMSvH@dhcp22.suse.cz>
 <20220923133512.GE22541@breakpoint.cc>
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On Fri 23-09-22 15:35:12, Florian Westphal wrote:
> Michal Hocko <mhocko@suse.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