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authorMaarten Lankhorst <maarten.lankhorst@linux.intel.com>2021-09-09 11:32:18 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-09-17 15:08:41 +0200
commit12235da8c80a1f9909008e4ca6036d5772b81192 (patch)
treeb6e9a7bbdc458e0909980e7b2194f9e80d092c05 /kernel/locking
parent6880fa6c56601bb8ed59df6c30fd390cc5f6dd8f (diff)
kernel/locking: Add context to ww_mutex_trylock()
i915 will soon gain an eviction path that trylock a whole lot of locks for eviction, getting dmesg failures like below: BUG: MAX_LOCK_DEPTH too low! turning off the locking correctness validator. depth: 48 max: 48! 48 locks held by i915_selftest/5776: #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] ... #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] INFO: lockdep is turned off. Fixing eviction to nest into ww_class_acquire is a high priority, but it requires a rework of the entire driver, which can only be done one step at a time. As an intermediate solution, add an acquire context to ww_mutex_trylock, which allows us to do proper nesting annotations on the trylocks, making the above lockdep splat disappear. This is also useful in regulator_lock_nested, which may avoid dropping regulator_nesting_mutex in the uncontended path, so use it there. TTM may be another user for this, where we could lock a buffer in a fastpath with list locks held, without dropping all locks we hold. [peterz: rework actual ww_mutex_trylock() implementations] Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/YUBGPdDDjKlxAuXJ@hirez.programming.kicks-ass.net
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/mutex.c41
-rw-r--r--kernel/locking/test-ww_mutex.c86
-rw-r--r--kernel/locking/ww_rt_mutex.c25
3 files changed, 131 insertions, 21 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index d456579d0952..2fede72b6af5 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -94,6 +94,9 @@ static inline unsigned long __owner_flags(unsigned long owner)
return owner & MUTEX_FLAGS;
}
+/*
+ * Returns: __mutex_owner(lock) on failure or NULL on success.
+ */
static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff)
{
unsigned long owner, curr = (unsigned long)current;
@@ -736,6 +739,44 @@ __ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass,
return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true);
}
+/**
+ * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
+ * @ww: mutex to lock
+ * @ww_ctx: optional w/w acquire context
+ *
+ * Trylocks a mutex with the optional acquire context; no deadlock detection is
+ * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
+ *
+ * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
+ * specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
+ *
+ * A mutex acquired with this function must be released with ww_mutex_unlock.
+ */
+int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
+{
+ if (!ww_ctx)
+ return mutex_trylock(&ww->base);
+
+ MUTEX_WARN_ON(ww->base.magic != &ww->base);
+
+ /*
+ * Reset the wounded flag after a kill. No other process can
+ * race and wound us here, since they can't have a valid owner
+ * pointer if we don't have any locks held.
+ */
+ if (ww_ctx->acquired == 0)
+ ww_ctx->wounded = 0;
+
+ if (__mutex_trylock(&ww->base)) {
+ ww_mutex_set_context_fastpath(ww, ww_ctx);
+ mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(ww_mutex_trylock);
+
#ifdef CONFIG_DEBUG_LOCK_ALLOC
void __sched
mutex_lock_nested(struct mutex *lock, unsigned int subclass)
diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 3e82f449b4ff..d63ac411f367 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -16,6 +16,15 @@
static DEFINE_WD_CLASS(ww_class);
struct workqueue_struct *wq;
+#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
+#define ww_acquire_init_noinject(a, b) do { \
+ ww_acquire_init((a), (b)); \
+ (a)->deadlock_inject_countdown = ~0U; \
+ } while (0)
+#else
+#define ww_acquire_init_noinject(a, b) ww_acquire_init((a), (b))
+#endif
+
struct test_mutex {
struct work_struct work;
struct ww_mutex mutex;
@@ -36,7 +45,7 @@ static void test_mutex_work(struct work_struct *work)
wait_for_completion(&mtx->go);
if (mtx->flags & TEST_MTX_TRY) {
- while (!ww_mutex_trylock(&mtx->mutex))
+ while (!ww_mutex_trylock(&mtx->mutex, NULL))
cond_resched();
} else {
ww_mutex_lock(&mtx->mutex, NULL);
@@ -109,19 +118,38 @@ static int test_mutex(void)
return 0;
}
-static int test_aa(void)
+static int test_aa(bool trylock)
{
struct ww_mutex mutex;
struct ww_acquire_ctx ctx;
int ret;
+ const char *from = trylock ? "trylock" : "lock";
ww_mutex_init(&mutex, &ww_class);
ww_acquire_init(&ctx, &ww_class);
- ww_mutex_lock(&mutex, &ctx);
+ if (!trylock) {
+ ret = ww_mutex_lock(&mutex, &ctx);
+ if (ret) {
+ pr_err("%s: initial lock failed!\n", __func__);
+ goto out;
+ }
+ } else {
+ if (!ww_mutex_trylock(&mutex, &ctx)) {
+ pr_err("%s: initial trylock failed!\n", __func__);
+ goto out;
+ }
+ }
- if (ww_mutex_trylock(&mutex)) {
- pr_err("%s: trylocked itself!\n", __func__);
+ if (ww_mutex_trylock(&mutex, NULL)) {
+ pr_err("%s: trylocked itself without context from %s!\n", __func__, from);
+ ww_mutex_unlock(&mutex);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ if (ww_mutex_trylock(&mutex, &ctx)) {
+ pr_err("%s: trylocked itself with context from %s!\n", __func__, from);
ww_mutex_unlock(&mutex);
ret = -EINVAL;
goto out;
@@ -129,17 +157,17 @@ static int test_aa(void)
ret = ww_mutex_lock(&mutex, &ctx);
if (ret != -EALREADY) {
- pr_err("%s: missed deadlock for recursing, ret=%d\n",
- __func__, ret);
+ pr_err("%s: missed deadlock for recursing, ret=%d from %s\n",
+ __func__, ret, from);
if (!ret)
ww_mutex_unlock(&mutex);
ret = -EINVAL;
goto out;
}
+ ww_mutex_unlock(&mutex);
ret = 0;
out:
- ww_mutex_unlock(&mutex);
ww_acquire_fini(&ctx);
return ret;
}
@@ -150,7 +178,7 @@ struct test_abba {
struct ww_mutex b_mutex;
struct completion a_ready;
struct completion b_ready;
- bool resolve;
+ bool resolve, trylock;
int result;
};
@@ -160,8 +188,13 @@ static void test_abba_work(struct work_struct *work)
struct ww_acquire_ctx ctx;
int err;
- ww_acquire_init(&ctx, &ww_class);
- ww_mutex_lock(&abba->b_mutex, &ctx);
+ ww_acquire_init_noinject(&ctx, &ww_class);
+ if (!abba->trylock)
+ ww_mutex_lock(&abba->b_mutex, &ctx);
+ else
+ WARN_ON(!ww_mutex_trylock(&abba->b_mutex, &ctx));
+
+ WARN_ON(READ_ONCE(abba->b_mutex.ctx) != &ctx);
complete(&abba->b_ready);
wait_for_completion(&abba->a_ready);
@@ -181,7 +214,7 @@ static void test_abba_work(struct work_struct *work)
abba->result = err;
}
-static int test_abba(bool resolve)
+static int test_abba(bool trylock, bool resolve)
{
struct test_abba abba;
struct ww_acquire_ctx ctx;
@@ -192,12 +225,18 @@ static int test_abba(bool resolve)
INIT_WORK_ONSTACK(&abba.work, test_abba_work);
init_completion(&abba.a_ready);
init_completion(&abba.b_ready);
+ abba.trylock = trylock;
abba.resolve = resolve;
schedule_work(&abba.work);
- ww_acquire_init(&ctx, &ww_class);
- ww_mutex_lock(&abba.a_mutex, &ctx);
+ ww_acquire_init_noinject(&ctx, &ww_class);
+ if (!trylock)
+ ww_mutex_lock(&abba.a_mutex, &ctx);
+ else
+ WARN_ON(!ww_mutex_trylock(&abba.a_mutex, &ctx));
+
+ WARN_ON(READ_ONCE(abba.a_mutex.ctx) != &ctx);
complete(&abba.a_ready);
wait_for_completion(&abba.b_ready);
@@ -249,7 +288,7 @@ static void test_cycle_work(struct work_struct *work)
struct ww_acquire_ctx ctx;
int err, erra = 0;
- ww_acquire_init(&ctx, &ww_class);
+ ww_acquire_init_noinject(&ctx, &ww_class);
ww_mutex_lock(&cycle->a_mutex, &ctx);
complete(cycle->a_signal);
@@ -581,7 +620,9 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
static int __init test_ww_mutex_init(void)
{
int ncpus = num_online_cpus();
- int ret;
+ int ret, i;
+
+ printk(KERN_INFO "Beginning ww mutex selftests\n");
wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
if (!wq)
@@ -591,17 +632,19 @@ static int __init test_ww_mutex_init(void)
if (ret)
return ret;
- ret = test_aa();
+ ret = test_aa(false);
if (ret)
return ret;
- ret = test_abba(false);
+ ret = test_aa(true);
if (ret)
return ret;
- ret = test_abba(true);
- if (ret)
- return ret;
+ for (i = 0; i < 4; i++) {
+ ret = test_abba(i & 1, i & 2);
+ if (ret)
+ return ret;
+ }
ret = test_cycle(ncpus);
if (ret)
@@ -619,6 +662,7 @@ static int __init test_ww_mutex_init(void)
if (ret)
return ret;
+ printk(KERN_INFO "All ww mutex selftests passed\n");
return 0;
}
diff --git a/kernel/locking/ww_rt_mutex.c b/kernel/locking/ww_rt_mutex.c
index 3f1fff7d2780..0e00205cf467 100644
--- a/kernel/locking/ww_rt_mutex.c
+++ b/kernel/locking/ww_rt_mutex.c
@@ -9,6 +9,31 @@
#define WW_RT
#include "rtmutex.c"
+int ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+ struct rt_mutex *rtm = &lock->base;
+
+ if (!ww_ctx)
+ return rt_mutex_trylock(rtm);
+
+ /*
+ * Reset the wounded flag after a kill. No other process can
+ * race and wound us here, since they can't have a valid owner
+ * pointer if we don't have any locks held.
+ */
+ if (ww_ctx->acquired == 0)
+ ww_ctx->wounded = 0;
+
+ if (__rt_mutex_trylock(&rtm->rtmutex)) {
+ ww_mutex_set_context_fastpath(lock, ww_ctx);
+ mutex_acquire_nest(&rtm->dep_map, 0, 1, ww_ctx->dep_map, _RET_IP_);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(ww_mutex_trylock);
+
static int __sched
__ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx,
unsigned int state, unsigned long ip)