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Date: Wed, 26 May 2021 10:33:42 +0200
From: Michal Suchánek <msuchanek@...e.de>
To: Mel Gorman <mgorman@...hsingularity.net>,
linux-kbuild@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Andrii Nakryiko <andrii.nakryiko@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
open list <linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Jiri Olsa <jolsa@...nel.org>,
Hritik Vijay <hritikxx8@...il.com>, bpf <bpf@...r.kernel.org>,
Linux-Net <netdev@...r.kernel.org>,
Linux-MM <linux-mm@...ck.org>,
Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: (BTF) [PATCH] mm/page_alloc: Work around a pahole limitation
with zero-sized struct pagesets
On Wed, May 26, 2021 at 09:07:41AM +0100, Mel Gorman wrote:
> Michal Suchanek reported the following problem with linux-next
>
> [ 0.000000] Linux version 5.13.0-rc2-next-20210519-1.g3455ff8-vanilla (geeko@...ldhost) (gcc (SUSE Linux) 10.3.0, GNU ld (GNU Binutils; openSUSE Tumbleweed) 2.36.1.20210326-3) #1 SMP Wed May 19 10:05:10 UTC 2021 (3455ff8)
> [ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.13.0-rc2-next-20210519-1.g3455ff8-vanilla root=UUID=ec42c33e-a2c2-4c61-afcc-93e9527 8f687 plymouth.enable=0 resume=/dev/disk/by-uuid/f1fe4560-a801-4faf-a638-834c407027c7 mitigations=auto earlyprintk initcall_debug nomodeset earlycon ignore_loglevel console=ttyS0,115200
> ...
> [ 26.093364] calling tracing_set_default_clock+0x0/0x62 @ 1
> [ 26.098937] initcall tracing_set_default_clock+0x0/0x62 returned 0 after 0 usecs
> [ 26.106330] calling acpi_gpio_handle_deferred_request_irqs+0x0/0x7c @ 1
> [ 26.113033] initcall acpi_gpio_handle_deferred_request_irqs+0x0/0x7c returned 0 after 3 usecs
> [ 26.121559] calling clk_disable_unused+0x0/0x102 @ 1
> [ 26.126620] initcall clk_disable_unused+0x0/0x102 returned 0 after 0 usecs
> [ 26.133491] calling regulator_init_complete+0x0/0x25 @ 1
> [ 26.138890] initcall regulator_init_complete+0x0/0x25 returned 0 after 0 usecs
> [ 26.147816] Freeing unused decrypted memory: 2036K
> [ 26.153682] Freeing unused kernel image (initmem) memory: 2308K
> [ 26.165776] Write protecting the kernel read-only data: 26624k
> [ 26.173067] Freeing unused kernel image (text/rodata gap) memory: 2036K
> [ 26.180416] Freeing unused kernel image (rodata/data gap) memory: 1184K
> [ 26.187031] Run /init as init process
> [ 26.190693] with arguments:
> [ 26.193661] /init
> [ 26.195933] with environment:
> [ 26.199079] HOME=/
> [ 26.201444] TERM=linux
> [ 26.204152] BOOT_IMAGE=/boot/vmlinuz-5.13.0-rc2-next-20210519-1.g3455ff8-vanilla
> [ 26.254154] BPF: type_id=35503 offset=178440 size=4
> [ 26.259125] BPF:
> [ 26.261054] BPF:Invalid offset
> [ 26.264119] BPF:
> [ 26.264119]
> [ 26.267437] failed to validate module [efivarfs] BTF: -22
>
> Andrii Nakryiko bisected the problem to the commit "mm/page_alloc: convert
> per-cpu list protection to local_lock" currently staged in mmotm. In his
> own words
>
> The immediate problem is two different definitions of numa_node per-cpu
> variable. They both are at the same offset within .data..percpu ELF
> section, they both have the same name, but one of them is marked as
> static and another as global. And one is int variable, while another
> is struct pagesets. I'll look some more tomorrow, but adding Jiri and
> Arnaldo for visibility.
>
> [110907] DATASEC '.data..percpu' size=178904 vlen=303
> ...
> type_id=27753 offset=163976 size=4 (VAR 'numa_node')
> type_id=27754 offset=163976 size=4 (VAR 'numa_node')
>
> [27753] VAR 'numa_node' type_id=27556, linkage=static
> [27754] VAR 'numa_node' type_id=20, linkage=global
>
> [20] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
>
> [27556] STRUCT 'pagesets' size=0 vlen=1
> 'lock' type_id=507 bits_offset=0
>
> [506] STRUCT '(anon)' size=0 vlen=0
> [507] TYPEDEF 'local_lock_t' type_id=506
>
> The patch in question introduces a zero-sized per-cpu struct and while
> this is not wrong, versions of pahole prior to 1.22 (unreleased) get
> confused during BTF generation with two separate variables occupying the
> same address.
>
> This patch checks for older versions of pahole and forces struct pagesets
> to be non-zero sized as a workaround when CONFIG_DEBUG_INFO_BTF is set. A
> warning is omitted so that distributions can update pahole when 1.22
> is released.
>
> Reported-by: Michal Suchanek <msuchanek@...e.de>
> Reported-by: Hritik Vijay <hritikxx8@...il.com>
> Debugged-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> ---
> lib/Kconfig.debug | 3 +++
> mm/page_alloc.c | 11 +++++++++++
> 2 files changed, 14 insertions(+)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 678c13967580..f88a155b80a9 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -313,6 +313,9 @@ config DEBUG_INFO_BTF
> config PAHOLE_HAS_SPLIT_BTF
> def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
>
> +config PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT
> + def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "122")
> +
This does not seem workable with dummy-tools.
Do we even have dummy pahole?
Thanks
Michal
> config DEBUG_INFO_BTF_MODULES
> def_bool y
> depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ff8f706839ea..1d56d3de8e08 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -124,6 +124,17 @@ static DEFINE_MUTEX(pcp_batch_high_lock);
>
> struct pagesets {
> local_lock_t lock;
> +#if defined(CONFIG_DEBUG_INFO_BTF) && \
> + !defined(CONFIG_DEBUG_LOCK_ALLOC) && \
> + !defined(CONFIG_PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT)
> + /*
> + * pahole 1.21 and earlier gets confused by zero-sized per-CPU
> + * variables and produces invalid BTF. Ensure that
> + * sizeof(struct pagesets) != 0 for older versions of pahole.
> + */
> + char __pahole_hack;
> + #warning "pahole too old to support zero-sized struct pagesets"
> +#endif
> };
> static DEFINE_PER_CPU(struct pagesets, pagesets) = {
> .lock = INIT_LOCAL_LOCK(lock),
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