linux-kernel - [PATCH v2 3/3] sched/wait: avoid double initialization in ___wait

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Date:   Mon,  2 Mar 2020 14:04:30 +0100
From:   glider@...gle.com
To:     tkjos@...gle.com, keescook@...omium.org,
        gregkh@...uxfoundation.org, arve@...roid.com, mingo@...hat.com
Cc:     dvyukov@...gle.com, jannh@...gle.com, devel@...verdev.osuosl.org,
        peterz@...radead.org, linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>
Subject: [PATCH v2 3/3] sched/wait: avoid double initialization in ___wait_event()

With CONFIG_INIT_STACK_ALL enabled, the local __wq_entry is initialized
twice. Because Clang is currently unable to optimize the automatic
initialization away (init_wait_entry() is defined in another translation
unit), remove it with the __no_initialize annotation.

Cc: Kees Cook <keescook@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Alexander Potapenko <glider@...gle.com>

---
 v2:
  - changed __do_not_initialize to __no_initialize as requested by Kees
    Cook
---
 drivers/android/binder.c | 4 ++--
 include/linux/wait.h     | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index a59871532ff6b..66984e7c33094 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4827,7 +4827,7 @@ static int binder_ioctl_write_read(struct file *filp,
 	struct binder_proc *proc = filp->private_data;
 	unsigned int size = _IOC_SIZE(cmd);
 	void __user *ubuf = (void __user *)arg;
-	struct binder_write_read bwr __no_initialize;
+	struct binder_write_read bwr;
 
 	if (size != sizeof(struct binder_write_read)) {
 		ret = -EINVAL;
@@ -5026,7 +5026,7 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			goto err;
 		break;
 	case BINDER_SET_MAX_THREADS: {
-		int max_threads;
+		int max_threads __no_initialize;
 
 		if (copy_from_user(&max_threads, ubuf,
 				   sizeof(max_threads))) {
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 3283c8d021377..b52a9bb2c7727 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -262,7 +262,8 @@ extern void init_wait_entry(struct wait_queue_entry *wq_entry, int flags);
 #define ___wait_event(wq_head, condition, state, exclusive, ret, cmd)		\
 ({										\
 	__label__ __out;							\
-	struct wait_queue_entry __wq_entry;					\
+	/* Unconditionally initialized by init_wait_entry(). */			\
+	struct wait_queue_entry __wq_entry __no_initialize;			\
 	long __ret = ret;	/* explicit shadow */				\
 										\
 	init_wait_entry(&__wq_entry, exclusive ? WQ_FLAG_EXCLUSIVE : 0);	\
-- 
2.25.0.265.gbab2e86ba0-goog