fs/select: rework stack allocation hack for clang

[ Upstream commit ddb9fd7a544088ed70eccbb9f85e9cc9952131c1 ]

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 <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240216202352.2492798-1-arnd@kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/select.c b/fs/select.c
index 5edffee1162c2423821e2282153a5ff1f3c985eb..668a5200503aec4d694b8d440b3719a869ff8744 100644 (file)
--- a/fs/select.c
+++ b/fs/select.c
@@ -475,7 +475,7 @@ 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 1cdc32b1f1b0836e6dccf2ecf446b9aeab0a950b..7e0fdcf905d2e77b355c94a7381446927452723c 100644 (file)
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -16,11 +16,7 @@
 extern struct ctl_table epoll_table[]; /* for sysctl */
 /* ~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