Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

[Linus Torvalds <torvalds@linux-foundation.org>]

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On Mon, Feb 28, 2022 at 12:03 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Side note: we do need *some* way to do it.

Ooh.

This patch is a work of art.

And I mean that in the worst possible way.

We can do

        typeof(pos) pos

in the 'for ()' loop, and never use __iter at all.

That means that inside the for-loop, we use a _different_ 'pos' than outside.

And then the compiler will not see some "might be uninitialized", but
the outer 'pos' *will* be uninitialized.

Unless, of course, the outer 'pos' had that pointless explicit initializer.

Here - can somebody poke holes in this "work of art" patch?

                     Linus

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 Makefile                       | 2 +-
 arch/x86/kernel/cpu/sgx/encl.c | 2 +-
 include/linux/list.h           | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index daeb5c88b50b..cc4b0a266af0 100644
--- a/Makefile
+++ b/Makefile
@@ -515,7 +515,7 @@ KBUILD_CFLAGS   := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
 		   -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE \
 		   -Werror=implicit-function-declaration -Werror=implicit-int \
 		   -Werror=return-type -Wno-format-security \
-		   -std=gnu89
+		   -std=gnu11
 KBUILD_CPPFLAGS := -D__KERNEL__
 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=
diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index 48afe96ae0f0..87db2f3936b0 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -450,7 +450,7 @@ static void sgx_mmu_notifier_release(struct mmu_notifier *mn,
 				     struct mm_struct *mm)
 {
 	struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm, mmu_notifier);
-	struct sgx_encl_mm *tmp = NULL;
+	struct sgx_encl_mm *tmp;
 
 	/*
 	 * The enclave itself can remove encl_mm.  Note, objects can't be moved
diff --git a/include/linux/list.h b/include/linux/list.h
index dd6c2041d09c..708078b2f24d 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -634,9 +634,9 @@ static inline void list_splice_tail_init(struct list_head *list,
  * @head:	the head for your list.
  * @member:	the name of the list_head within the struct.
  */
-#define list_for_each_entry(pos, head, member)				\
-	for (pos = list_first_entry(head, typeof(*pos), member);	\
-	     !list_entry_is_head(pos, head, member);			\
+#define list_for_each_entry(pos, head, member)					\
+	for (typeof(pos) pos = list_first_entry(head, typeof(*pos), member);	\
+	     !list_entry_is_head(pos, head, member);	\
 	     pos = list_next_entry(pos, member))
 
 /**