On Thu, 2017-03-02 at 23:22 +0100, Arnd Bergmann wrote: > On Thu, Mar 2, 2017 at 6:46 PM, Joe Perches <j...@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.
These logging functions aren't inlined. You're referring to the stack frame? > > > 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: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: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=] Still doesn't make sense to me. None of the logging functions are inlined as they are all EXPORT_SYMBOL. This just changes a pointer to a u64, which is the same size on x86-64 (and is of course larger on x86-32). Perhaps KASAN has the odd behavior and working around KASAN's behavior may not be the proper thing to do. Maybe if CONFIG_KASAN is set, the minimum stack should be increased via THREAD_SIZE_ORDER or some such.
