[072/166] mm/shmem.c: distribute switch variables for initialization
diff mbox series

Message ID 20200407030751.w0w2M3QVA%akpm@linux-foundation.org
State New
Headers show
  • [001/166] mm, memcg: bypass high reclaim iteration for cgroup hierarchy root
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Commit Message

Andrew Morton April 7, 2020, 3:07 a.m. UTC
From: Kees Cook <keescook@chromium.org>
Subject: mm/shmem.c: distribute switch variables for initialization

Variables declared in a switch statement before any case statements cannot
be automatically initialized with compiler instrumentation (as they are
not part of any execution flow).  With GCC's proposed automatic stack
variable initialization feature, this triggers a warning (and they don't
get initialized).  Clang's automatic stack variable initialization (via
CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also doesn't
initialize such variables[1].  Note that these warnings (or silent
skipping) happen before the dead-store elimination optimization phase, so
even when the automatic initializations are later elided in favor of
direct initializations, the warnings remain.

To avoid these problems, move such variables into the "case" where they're
used or lift them up into the main function body.

mm/shmem.c: In function `shmem_getpage_gfp':
mm/shmem.c:1816:10: warning: statement will never be executed [-Wswitch-unreachable]
 1816 |   loff_t i_size;
      |          ^~~~~~

[1] https://bugs.llvm.org/show_bug.cgi?id=44916

Link: http://lkml.kernel.org/r/20200220062312.69165-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 mm/shmem.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff mbox series

--- a/mm/shmem.c~shmem-distribute-switch-variables-for-initialization
+++ a/mm/shmem.c
@@ -1812,17 +1812,20 @@  repeat:
 	if (shmem_huge == SHMEM_HUGE_FORCE)
 		goto alloc_huge;
 	switch (sbinfo->huge) {
-		loff_t i_size;
-		pgoff_t off;
 		goto alloc_nohuge;
+		loff_t i_size;
+		pgoff_t off;
 		off = round_up(index, HPAGE_PMD_NR);
 		i_size = round_up(i_size_read(inode), PAGE_SIZE);
 		if (i_size >= HPAGE_PMD_SIZE &&
 		    i_size >> PAGE_SHIFT >= off)
 			goto alloc_huge;
-		/* fallthrough */
+		fallthrough;
+	}
 		if (sgp_huge == SGP_HUGE)
 			goto alloc_huge;