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Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN

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On Thu, Mar 2, 2017 at 6:46 PM, Joe Perches <joe@perches.com> wrote:
> On Thu, 2017-03-02 at 17:38 +0100, Arnd Bergmann wrote:
>> The internal logging infrastructure in ocfs2 causes special warning code to be
>> used with KASAN, which produces rather large stack frames:
>
>> fs/ocfs2/super.c: In function 'ocfs2_fill_super':
>> fs/ocfs2/super.c:1219:1: error: the frame size of 3264 bytes is larger than 3072 bytes [-Werror=frame-larger-than=]
>
> At least by default it doesn't seem to.
>
> gcc 6.2 allyesconfig, CONFIG_KASAN=y
> with either CONFIG_KASAN_INLINE or CONFIG_KASAN_OUTLINE
>
> gcc doesn't emit a stack warning

The warning is disabled until patch 26/26. which picks the 3072 default.
The 3264 number was with gcc-7, which is worse than gcc-6 since it enables
an extra check.

>> By simply passing the mask by value instead of reference, we can avoid the
>> problem completely.
>
> Any idea why that's so?

With KASAN, every time we inline the function, the compiler has to allocate
space for another copy of the variable plus a redzone to detect whether
passing it by reference into another function causes an overflow at runtime.

>>  On 64-bit architectures, this is also more efficient,
>
> Efficient true, but the same overall stack no?

Here is what I see with CONFIG_FRAME_WARN=300 and x86_64-linux-gcc-6.3.1:

before:
fs/ocfs2/super.c: In function 'ocfs2_parse_options.isra.3':
fs/ocfs2/super.c:1508:1: error: the frame size of 352 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_enable_quotas':
fs/ocfs2/super.c:974:1: error: the frame size of 344 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_fill_super':
fs/ocfs2/super.c:1219:1: error: the frame size of 552 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]

after:
fs/ocfs2/super.c: In function 'ocfs2_fill_super':
fs/ocfs2/super.c:1219:1: error: the frame size of 472 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]

and with gcc-7.0.1 (including -fsanitize-address-use-after-scope), before:
fs/ocfs2/super.c: In function 'ocfs2_check_volume':
fs/ocfs2/super.c:2512:1: error: the frame size of 768 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_statfs':
fs/ocfs2/super.c:1717:1: error: the frame size of 320 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_parse_options.isra.3':
fs/ocfs2/super.c:1508:1: error: the frame size of 464 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_enable_quotas':
fs/ocfs2/super.c:974:1: error: the frame size of 320 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_remount':
fs/ocfs2/super.c:752:1: error: the frame size of 568 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_initialize_super.isra.8':
fs/ocfs2/super.c:2339:1: error: the frame size of 1712 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]
fs/ocfs2/super.c: In function 'ocfs2_fill_super':
fs/ocfs2/super.c:1219:1: error: the frame size of 3264 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]

after:
fs/ocfs2/super.c: In function 'ocfs2_fill_super':
fs/ocfs2/super.c:1219:1: error: the frame size of 704 bytes is larger
than 300 bytes [-Werror=frame-larger-than=]

     Arnd

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[PATCH 00/26] bring back stack frame warning with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:50 +0100
      Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:00 +0100
        Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 12:20 +0100
          Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:20 +0100
            Re: [PATCH 07/26] brcmsmac: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-06 12:40 +0100
  [PATCH 15/26] [media] tuners: i2c: reduce stack usage for tuner_i2c_xfer_* Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 11/26] rtlwifi: reduce stack usage for KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 04/26] tty: kbd: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 12/26] wl3501_cs: reduce stack size for KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 09/26] brcmsmac: split up wlc_phy_workarounds_nphy Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 09/26] brcmsmac: split up wlc_phy_workarounds_nphy Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:40 +0100
  [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Alexander Potapenko <glider@google.com> - 2017-03-03 15:00 +0100
      Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Alexander Potapenko <glider@google.com> - 2017-03-03 15:40 +0100
        Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-03 16:10 +0100
      Re: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation Arnd Bergmann <arnd@arndb.de> - 2017-03-03 15:40 +0100
    RE: [PATCH 01/26] compiler: introduce noinline_for_kasan annotation David Laight <David.Laight@ACULAB.COM> - 2017-03-03 18:10 +0100
  [PATCH 05/26] netlink: mark nla_put_{u8,u16,u32} noinline_for_kasan Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
  [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:20 +0100
    Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-06 10:40 +0100
      Re: [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Kalle Valo <kvalo@codeaurora.org> - 2017-03-06 17:40 +0100
        Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arnd Bergmann <arnd@arndb.de> - 2017-03-06 22:40 +0100
          Re: [PATCH 08/26] brcmsmac: make some local variables 'static const' to reduce stack size Kalle Valo <kvalo@codeaurora.org> - 2017-03-07 10:50 +0100
            Re: [PATCH 08/26] brcmsmac: make some local variables 'static const'  to reduce stack size Arend Van Spriel <arend.vanspriel@broadcom.com> - 2017-03-07 11:10 +0100
  [PATCH 22/26] drm/i915/gvt: don't overflow the kernel stack with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 18:40 +0100
  Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-02 19:00 +0100
    Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-02 23:50 +0100
      Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:10 +0100
        Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Joe Perches <joe@perches.com> - 2017-03-03 01:00 +0100
    Re: [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 00:00 +0100
  [PATCH 24/26] ocfs2: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 20:10 +0100
  [PATCH 23/26] mtd: cfi: reduce stack size with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 20:20 +0100
  [PATCH 18/26] [media] i2c: cx25840: avoid stack overflow with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-02 23:30 +0100
  Re: [PATCH 00/26] bring back stack frame warning with KASAN Alexander Potapenko <glider@google.com> - 2017-03-03 13:30 +0100
    Re: [PATCH 00/26] bring back stack frame warning with KASAN Arnd Bergmann <arnd@arndb.de> - 2017-03-03 14:00 +0100
  Re: [PATCH 10/26] brcmsmac: reindent split functions Kalle Valo <kvalo@codeaurora.org> - 2017-03-06 17:50 +0100

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