Re: [3.11-rc1] CONFIG_DEBUG_MUTEXES=y using gcc 3.x makes unbootablekernel.

From: Tetsuo Handa
Date: Mon Sep 09 2013 - 07:57:19 EST

Maarten Lankhorst wrote:
> Almost correct. I meant passing it as parameter to __mutex_lock_common. Your version will still cause an extra pointless null check in the ww_mutex_lock case.

Ah, I see.
----------
>From 95f189eb37c25ddf8e48d5dfc2f9f1185c52b6a8 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 9 Sep 2013 20:48:13 +0900
Subject: [PATCH] mutex: Avoid gcc version dependent __builtin_constant_p() usage.

Commit 040a0a37 "mutex: Add support for wound/wait style locks" used
"!__builtin_constant_p(p == NULL)" but gcc 3.x cannot handle such expression
correctly, leading to boot failure when built with CONFIG_DEBUG_MUTEXES=y.

Fix it by explicitly passing a bool which tells whether p != NULL or not.

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxx> [3.11+]
---
kernel/mutex.c | 32 ++++++++++++++++----------------
1 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/kernel/mutex.c b/kernel/mutex.c
index a52ee7bb..a2b80f1 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -408,7 +408,7 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock,
static __always_inline int __sched
__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct lockdep_map *nest_lock, unsigned long ip,
- struct ww_acquire_ctx *ww_ctx)
+ struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
{
struct task_struct *task = current;
struct mutex_waiter waiter;
@@ -448,7 +448,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct task_struct *owner;
struct mspin_node node;

- if (!__builtin_constant_p(ww_ctx == NULL) && ww_ctx->acquired > 0) {
+ if (use_ww_ctx && ww_ctx->acquired > 0) {
struct ww_mutex *ww;

ww = container_of(lock, struct ww_mutex, base);
@@ -478,7 +478,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
if ((atomic_read(&lock->count) == 1) &&
(atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
lock_acquired(&lock->dep_map, ip);
- if (!__builtin_constant_p(ww_ctx == NULL)) {
+ if (use_ww_ctx) {
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);

@@ -548,7 +548,7 @@ slowpath:
goto err;
}

- if (!__builtin_constant_p(ww_ctx == NULL) && ww_ctx->acquired > 0) {
+ if (use_ww_ctx && ww_ctx->acquired > 0) {
ret = __mutex_lock_check_stamp(lock, ww_ctx);
if (ret)
goto err;
@@ -568,7 +568,7 @@ done:
mutex_remove_waiter(lock, &waiter, current_thread_info());
mutex_set_owner(lock);

- if (!__builtin_constant_p(ww_ctx == NULL)) {
+ if (use_ww_ctx) {
struct ww_mutex *ww = container_of(lock,
struct ww_mutex,
base);
@@ -618,7 +618,7 @@ mutex_lock_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
- subclass, NULL, _RET_IP_, NULL);
+ subclass, NULL, _RET_IP_, NULL, 0);
}

EXPORT_SYMBOL_GPL(mutex_lock_nested);
@@ -628,7 +628,7 @@ _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
{
might_sleep();
__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
- 0, nest, _RET_IP_, NULL);
+ 0, nest, _RET_IP_, NULL, 0);
}

EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
@@ -638,7 +638,7 @@ mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
return __mutex_lock_common(lock, TASK_KILLABLE,
- subclass, NULL, _RET_IP_, NULL);
+ subclass, NULL, _RET_IP_, NULL, 0);
}
EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);

@@ -647,7 +647,7 @@ mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
- subclass, NULL, _RET_IP_, NULL);
+ subclass, NULL, _RET_IP_, NULL, 0);
}

EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
@@ -685,7 +685,7 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

might_sleep();
ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
- 0, &ctx->dep_map, _RET_IP_, ctx);
+ 0, &ctx->dep_map, _RET_IP_, ctx, 1);
if (!ret && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);

@@ -700,7 +700,7 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

might_sleep();
ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
- 0, &ctx->dep_map, _RET_IP_, ctx);
+ 0, &ctx->dep_map, _RET_IP_, ctx, 1);

if (!ret && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
@@ -812,28 +812,28 @@ __mutex_lock_slowpath(atomic_t *lock_count)
struct mutex *lock = container_of(lock_count, struct mutex, count);

__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
- NULL, _RET_IP_, NULL);
+ NULL, _RET_IP_, NULL, 0);
}

static noinline int __sched
__mutex_lock_killable_slowpath(struct mutex *lock)
{
return __mutex_lock_common(lock, TASK_KILLABLE, 0,
- NULL, _RET_IP_, NULL);
+ NULL, _RET_IP_, NULL, 0);
}

static noinline int __sched
__mutex_lock_interruptible_slowpath(struct mutex *lock)
{
return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
- NULL, _RET_IP_, NULL);
+ NULL, _RET_IP_, NULL, 0);
}

static noinline int __sched
__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
- NULL, _RET_IP_, ctx);
+ NULL, _RET_IP_, ctx, 1);
}

static noinline int __sched
@@ -841,7 +841,7 @@ __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
- NULL, _RET_IP_, ctx);
+ NULL, _RET_IP_, ctx, 1);
}

#endif
--
1.7.8
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