Subject: [PATCH v3] mm/page_alloc: Require pahole v1.22 to cope with zero-sized struct pagesets

From: Mel Gorman <[email-masked]>
Date: Thu, 27 May 2021 18:19:23 +0100

This patch replaces
mm-page_alloc-convert-per-cpu-list-protection-to-local_lock-fix.patch in
Andrew's tree.

Michal Suchanek reported the following problem with linux-next

  [    0.000000] Linux version 5.13.0-rc2-next-20210519-1.g3455ff8-vanilla (geeko@buildhost) (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 get confused during
BTF generation with two separate variables occupying the same address.

This patch adds a requirement for pahole 1.22 before setting
DEBUG_INFO_BTF.  While pahole 1.22 does not exist yet, a fix is in the
pahole git tree as ("btf_encoder: fix and complete filtering out zero-sized
per-CPU variables").

Reported-by: Michal Suchanek <[email-masked]>
Reported-by: Hritik Vijay <[email-masked]>
Debugged-by: Andrii Nakryiko <[email-masked]>
Signed-off-by: Mel Gorman <[email-masked]>
---
 lib/Kconfig.debug | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 678c13967580..825be101767e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -301,10 +301,14 @@ config DEBUG_INFO_DWARF5
 
 endchoice # "DWARF version"
 
+config PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT
+	def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "122")
+
 config DEBUG_INFO_BTF
 	bool "Generate BTF typeinfo"
 	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
 	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
+	depends on PAHOLE_HAS_ZEROSIZE_PERCPU_SUPPORT
 	help
 	  Generate deduplicated BTF type information from DWARF debug info.
 	  Turning this on expects presence of pahole tool, which will convert