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Date:   Wed, 8 Jun 2022 22:19:32 -0700
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     Vasily Averin <vvs@openvz.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Shakeel Butt <shakeelb@google.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        regressions@lists.linux.dev, lkft-triage@lists.linaro.org,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Raghuram Thammiraju <raghuram.thammiraju@arm.com>,
        Mark Brown <broonie@kernel.org>, Will Deacon <will@kernel.org>,
        Qian Cai <quic_qiancai@quicinc.com>
Subject: Re: [next] arm64: boot failed - next-20220606
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On Thu, Jun 09, 2022 at 12:43:00PM +0800, Kefeng Wang wrote:
> 
> On 2022/6/9 11:44, Kefeng Wang wrote:
> > 
> > On 2022/6/9 10:49, Vasily Averin wrote:
> > > Dear ARM developers,
> > > could you please help me to find the reason of this problem?
> > Hi,
> > > mem_cgroup_from_obj():
> > > ffff80000836cf40:?????? d503245f??????? bti???? c
> > > ffff80000836cf44:?????? d503201f??????? nop
> > > ffff80000836cf48:?????? d503201f??????? nop
> > > ffff80000836cf4c:?????? d503233f??????? paciasp
> > > ffff80000836cf50:?????? d503201f??????? nop
> > > ffff80000836cf54:?????? d2e00021??????? mov???? x1,
> > > #0x1000000000000??????????? // #281474976710656
> > > ffff80000836cf58:?????? 8b010001??????? add???? x1, x0, x1
> > > ffff80000836cf5c:?????? b25657e4??????? mov???? x4,
> > > #0xfffffc0000000000???????? // #-4398046511104
> > > ffff80000836cf60:?????? d34cfc21??????? lsr???? x1, x1, #12
> > > ffff80000836cf64:?????? d37ae421??????? lsl???? x1, x1, #6
> > > ffff80000836cf68:?????? 8b040022??????? add???? x2, x1, x4
> > > ffff80000836cf6c:?????? f9400443??????? ldr???? x3, [x2, #8]
> > > 
> > > x5 : ffff80000a96f000 x4 : fffffc0000000000 x3 : ffff80000ad5e680
> > > x2 : fffffe00002bc240 x1 : 00000200002bc240 x0 : ffff80000af09740
> > > 
> > > x0 = 0xffff80000af09740 is an argument of mem_cgroup_from_obj()
> > > according to System.map it is init_net
> > > 
> > > This issue is caused by calling virt_to_page() on address of static
> > > variable init_net.
> > > Arm64 consider that addresses of static variables are not valid
> > > virtual addresses.
> > > On x86_64 the same API works without any problem.
> > > 
> > > Unfortunately I do not understand the cause of the problem.
> > > I do not see any bugs in my patch.
> > > I'm using an existing API, mem_cgroup_from_obj(), to find the memory
> > > cgroup used
> > > to account for the specified object.
> > > In particular, in the current case, I wanted to get the memory
> > > cgroup of the
> > > specified network namespace by the name taken from for_each_net().
> > > The first object in this list is the static structure unit_net
> > 
> > root@test:~# cat /proc/kallsyms |grep -w _data
> > ffff80000a110000 D _data
> > root@test:~# cat /proc/kallsyms |grep -w _end
> > ffff80000a500000 B _end
> > root@test:~# cat /proc/kallsyms |grep -w init_net
> > ffff80000a4eb980 B init_net
> > 
> > the init_net is located in data section, on arm64, it is allowed by
> > vmalloc, see
> > 
> > ??? map_kernel_segment(pgdp, _data, _end, PAGE_KERNEL, &vmlinux_data, 0,
> > 0);
> > 
> > and the arm has same behavior.
> > 
> > We could let init_net be allocated dynamically, but I think it could
> > change a lot.
> > 
> > Any better sugguestion, Catalin?
> 
> or? add vmalloc check in mem_cgroup_from_obj()?
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 27cebaa53472..fb817e5da5f0 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2860,7 +2860,10 @@ struct mem_cgroup *mem_cgroup_from_obj(void *p)
> ??????? if (mem_cgroup_disabled())
> ??????????????? return NULL;
> 
> -?????? folio = virt_to_folio(p);
> +?????? if (unlikely(is_vmalloc_addr(p)))
> +?????????????? folio = page_folio(vmalloc_to_page(p));
> +?????? else
> +?????????????? folio = virt_to_folio(p);
> 
> ??????? /*
> ???????? * Slab objects are accounted individually, not per-page.
> 

It sounds right. Later we can add something like mem_cgroup_from_slab_obj()
to use on hot paths and avoid this check.