From ddb9fd7a544088ed70eccbb9f85e9cc9952131c1 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann Date: Fri, 16 Feb 2024 21:23:34 +0100 Subject: [PATCH] fs/select: rework stack allocation hack for clang A while ago, we changed the way that select() and poll() preallocate a temporary buffer just under the size of the static warning limit of 1024 bytes, as clang was frequently going slightly above that limit. The warnings have recently returned and I took another look. As it turns out, clang is not actually inherently worse at reserving stack space, it just happens to inline do_select() into core_sys_select(), while gcc never inlines it. Annotate do_select() to never be inlined and in turn remove the special case for the allocation size. This should give the same behavior for both clang and gcc all the time and once more avoids those warnings. Fixes: ad312f95d41c ("fs/select: avoid clang stack usage warning") Signed-off-by: Arnd Bergmann Link: https://lore.kernel.org/r/20240216202352.2492798-1-arnd@kernel.org Reviewed-by: Kees Cook Reviewed-by: Andi Kleen Reviewed-by: Jan Kara Signed-off-by: Christian Brauner --- fs/select.c | 2 +- include/linux/poll.h | 4 ---- 2 files changed, 1 insertion(+), 5 deletions(-) diff --git a/fs/select.c b/fs/select.c index 11a3b1312abe..9515c3fa1a03 100644 --- a/fs/select.c +++ b/fs/select.c @@ -476,7 +476,7 @@ static inline void wait_key_set(poll_table *wait, unsigned long in, wait->_key |= POLLOUT_SET; } -static int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time) +static noinline_for_stack int do_select(int n, fd_set_bits *fds, struct timespec64 *end_time) { ktime_t expire, *to = NULL; struct poll_wqueues table; diff --git a/include/linux/poll.h b/include/linux/poll.h index a9e0e1c2d1f2..d1ea4f3714a8 100644 --- a/include/linux/poll.h +++ b/include/linux/poll.h @@ -14,11 +14,7 @@ /* ~832 bytes of stack space used max in sys_select/sys_poll before allocating additional memory. */ -#ifdef __clang__ -#define MAX_STACK_ALLOC 768 -#else #define MAX_STACK_ALLOC 832 -#endif #define FRONTEND_STACK_ALLOC 256 #define SELECT_STACK_ALLOC FRONTEND_STACK_ALLOC #define POLL_STACK_ALLOC FRONTEND_STACK_ALLOC