Commit ad312f95 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Linus Torvalds

fs/select: avoid clang stack usage warning

The select() implementation is carefully tuned to put a sensible amount
of data on the stack for holding a copy of the user space fd_set, but
not too large to risk overflowing the kernel stack.

When building a 32-bit kernel with clang, we need a little more space
than with gcc, which often triggers a warning:

  fs/select.c:619:5: error: stack frame size of 1048 bytes in function 'core_sys_select' [-Werror,-Wframe-larger-than=]
  int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,

I experimentally found that for 32-bit ARM, reducing the maximum stack
usage by 64 bytes keeps us reliably under the warning limit again.

Link: http://lkml.kernel.org/r/20190307090146.1874906-1-arnd@arndb.deSigned-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Reviewed-by: default avatarAndi Kleen <ak@linux.intel.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Eric Dumazet <edumazet@google.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 134fca90
......@@ -16,7 +16,11 @@
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
......
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