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Message-Id: <1482346000-9927-5-git-send-email-nhaehnle@gmail.com>
Date: Wed, 21 Dec 2016 19:46:32 +0100
From: Nicolai Hähnle <nhaehnle@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Nicolai Hähnle <Nicolai.Haehnle@....com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Maarten Lankhorst <dev@...ankhorst.nl>,
Daniel Vetter <daniel@...ll.ch>,
Chris Wilson <chris@...is-wilson.co.uk>,
dri-devel@...ts.freedesktop.org
Subject: [PATCH v3 04/12] locking/ww_mutex: Set use_ww_ctx even when locking without a context
From: Nicolai Hähnle <Nicolai.Haehnle@....com>
We will add a new field to struct mutex_waiter. This field must be
initialized for all waiters if any waiter uses the ww_use_ctx path.
So there is a trade-off: Keep ww_mutex locking without a context on the
faster non-use_ww_ctx path, at the cost of adding the initialization to all
mutex locks (including non-ww_mutexes), or avoid the additional cost for
non-ww_mutex locks, at the cost of adding additional checks to the
use_ww_ctx path.
We take the latter choice. It may be worth eliminating the users of
ww_mutex_lock(lock, NULL), but there are a lot of them.
v3:
- undo the moving around of ww in __mutex_lock_common
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Maarten Lankhorst <dev@...ankhorst.nl>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: dri-devel@...ts.freedesktop.org
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@....com>
---
include/linux/ww_mutex.h | 11 ++---------
kernel/locking/mutex.c | 29 +++++++++++++++++------------
2 files changed, 19 insertions(+), 21 deletions(-)
diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h
index 2bb5deb..a5960e5 100644
--- a/include/linux/ww_mutex.h
+++ b/include/linux/ww_mutex.h
@@ -222,11 +222,7 @@ extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,
*/
static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
{
- if (ctx)
- return __ww_mutex_lock(lock, ctx);
-
- mutex_lock(&lock->base);
- return 0;
+ return __ww_mutex_lock(lock, ctx);
}
/**
@@ -262,10 +258,7 @@ static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ct
static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)
{
- if (ctx)
- return __ww_mutex_lock_interruptible(lock, ctx);
- else
- return mutex_lock_interruptible(&lock->base);
+ return __ww_mutex_lock_interruptible(lock, ctx);
}
/**
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 66718d6..a41bec2 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -467,7 +467,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
for (;;) {
struct task_struct *owner;
- if (use_ww_ctx && ww_ctx->acquired > 0) {
+ if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
struct ww_mutex *ww;
ww = container_of(lock, struct ww_mutex, base);
@@ -635,8 +635,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct ww_mutex *ww;
int ret;
- if (use_ww_ctx) {
- ww = container_of(lock, struct ww_mutex, base);
+ ww = container_of(lock, struct ww_mutex, base);
+
+ if (use_ww_ctx && ww_ctx) {
if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
return -EALREADY;
}
@@ -648,7 +649,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
/* got the lock, yay! */
lock_acquired(&lock->dep_map, ip);
- if (use_ww_ctx)
+ if (use_ww_ctx && ww_ctx)
ww_mutex_set_context_fastpath(ww, ww_ctx);
preempt_enable();
return 0;
@@ -694,7 +695,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
goto err;
}
- if (use_ww_ctx && ww_ctx->acquired > 0) {
+ if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
if (ret)
goto err;
@@ -735,7 +736,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
/* got the lock - cleanup and rejoice! */
lock_acquired(&lock->dep_map, ip);
- if (use_ww_ctx)
+ if (use_ww_ctx && ww_ctx)
ww_mutex_set_context_slowpath(ww, ww_ctx);
spin_unlock_mutex(&lock->wait_lock, flags);
@@ -823,8 +824,9 @@ __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, 1);
- if (!ret && ctx->acquired > 1)
+ 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+ ctx, 1);
+ if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
@@ -838,9 +840,10 @@ __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, 1);
+ 0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+ ctx, 1);
- if (!ret && ctx->acquired > 1)
+ if (!ret && ctx && ctx->acquired > 1)
return ww_mutex_deadlock_injection(lock, ctx);
return ret;
@@ -1027,7 +1030,8 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
might_sleep();
if (__mutex_trylock_fast(&lock->base)) {
- ww_mutex_set_context_fastpath(lock, ctx);
+ if (ctx)
+ ww_mutex_set_context_fastpath(lock, ctx);
return 0;
}
@@ -1041,7 +1045,8 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
might_sleep();
if (__mutex_trylock_fast(&lock->base)) {
- ww_mutex_set_context_fastpath(lock, ctx);
+ if (ctx)
+ ww_mutex_set_context_fastpath(lock, ctx);
return 0;
}
--
2.7.4
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