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Effectively a revert of commitad312f95d4("fs/select: avoid clang stack usage warning") Various configs can still push the stack useage of core_sys_select() over the CONFIG_FRAME_WARN threshold (1024B on 32b targets). fs/select.c:619:5: error: stack frame size of 1048 bytes in function 'core_sys_select' [-Werror,-Wframe-larger-than=] core_sys_select() has a large stack allocation for `stack_fds` where it tries to do something equivalent to "small string optimization" to potentially avoid a kmalloc. core_sys_select() calls do_select() which has another potentially large stack allocation, `table`. Both of these values depend on FRONTEND_STACK_ALLOC. Mix those two large allocation with register spills which are exacerbated by various configs and compiler versions and we can just barely exceed the 1024B limit. Rather than keep trying to find the right value of MAX_STACK_ALLOC or FRONTEND_STACK_ALLOC, mark do_select() as noinline_for_stack. The intent of FRONTEND_STACK_ALLOC is to help potentially avoid a dynamic memory allocation. In that spirit, restore the previous threshold but separate the stack frames. Many tests of various configs for different architectures and various versions of GCC were performed; do_select() was never inlined into core_sys_select() or compat_core_sys_select(). The kernel is built with the GCC specific flag `-fconserve-stack` which can limit inlining depending on per-target thresholds of callee stack size, which helps avoid the issue when using GCC. Clang is being more aggressive and not considering the stack size when decided whether to inline or not. We may consider using the clang-16+ flag `-finline-max-stacksize=` in the future. Link: https://lore.kernel.org/lkml/20221006222124.aabaemy7ofop7ccz@google.com/ Fixes:ad312f95d4("fs/select: avoid clang stack usage warning") Suggested-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Bug: 250930332 Link: https://lore.kernel.org/llvm/20221011205547.14553-1-ndesaulniers@google.com/ Change-Id: I97d68bd05ec3ae5f6c09fc29055b9f88735c8cd6