From nobody Sat Feb 7 15:10:40 2026 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B0A8B1BF7E8 for ; Mon, 25 Nov 2024 19:52:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732564332; cv=none; b=tGEZNt0YZXXVEgFLEu7lDkWg32JdE8xU6Ougvk8vNws+0vui6SsUYmKb2mlxK+/Jgy0f/txbZVd6FfD48umlCZ9UuE4rez/YS7izrHAiAS/FiGYKoUU006PAax4YAjqrkuutVXqK8atk/PSg2PsslE54wF+UF92PojazeUgLIUE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732564332; c=relaxed/simple; bh=xyZ12uWc11HrkARvtSL1yJv5GPBzvsXBQDaclEx5iuk=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=N27nqWdXG0A/g9W3NpPGvVvxAB/wAN4Gm7iWXyI1+J3shXFvJjgxvd0TxDDenBMN2dTutc00qwws7MiIVznJODHX7zMxQ3zqwHqqYJSRL9ddzqoeuYn18B7D6r+CE3Q2stB2z13KfS6qqB4TkWKhKC0WgCj2IZ8zId03lLoiDOg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ikLesNxL; arc=none smtp.client-ip=209.85.214.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--jstultz.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ikLesNxL" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-212a337cf0bso33456865ad.0 for ; Mon, 25 Nov 2024 11:52:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1732564330; x=1733169130; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=/LKBY/kpPXDrgd01Wy0hrPJQtD2fGMqawNoGE5KKOdE=; b=ikLesNxLVseK1v7bq41g6cCFFsmTifdrha4dYjmDaQo+UZIwq26UCvKx9Ysa7DvFRv LVdhSbZyjZRr6eXLJa9fQ0h9S/sJw517RLO0yClbzm3yLZEhtY/nB0K2iSHcPapQ7QdF si2fKRHjRuHufXKvSq6MC7qW79BhBff+NxXjOxNKpeHRnGvd3e5aDX7dPHs4glx0fXMc XU5vIlBQjlE7O0cfiee9gr6Ae4x1JxiIntGSEgvhmBsIFbwypwjoQxnrV/w334m4mGfC nm7Vf6XsnekVUjp9Ay20bUQ07zzOsfb8PJeOrvhoowN7AHFo36bXJcqJQ/2fMk11V9zG pqcA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732564330; x=1733169130; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=/LKBY/kpPXDrgd01Wy0hrPJQtD2fGMqawNoGE5KKOdE=; b=egDYa3lmbhIq46HyXKSG9yzWaiBeg7WIEf77xH+vOtU2PVNduLOO9o92X6xw76wxgO lIz7kkHYkOwuqNAIw823mRIrMsBBsc42WJjfTte5IlEijAY7pvT/ij6g4byyD2RzPzet kgRVX3PVU9RcdPCznMgDghaN3PGQ+6b8O+9P3guORH6YZl3gRHV6KwVG2rcrxyx+8akg rNJ6PZF+1ggw7wq+4xe7vT/jSmHjj3anidX6+ubNAVF6Bn5UpdbC+/5J7BnBJHw9Dsgw TvuYvoW+OEu3GfBBXx49pD9xfBi2taf1FIxO7PNWy1fyV8kMSpY9/B9b5+v+GRMYx3Wi de6g== X-Gm-Message-State: AOJu0YwtHa4nAY4zaS1XFy1vf7klfDvVL+V5LmkIZ2tpCbrIRPiPZYeF aVW+xe/Xlxnn1Tj8uaHCYvldR2LgPqeULRPP5MRzR2+BM1eGGEHepTREUJ0QbXL/uSZxQmWInZo qW+ilWojS9RHL4CKYg0DZDvf1UX75aF0UUpDZ20Z6bdze5fh30uAztkrpZ0QYdcmQ89AlAU3H5y Vlcn1vyaMXB2MwBHiuMzhOecZAPnG262/BSHhBGkSlZbuv X-Google-Smtp-Source: AGHT+IE+RMYGzLs6IPrxwch9JnbbYVK9DgFEwAHd9/qSzhKRkT1ZDF/SmDMf9RpBf6yyKgPg02niQ0oHTM54 X-Received: from plbkd8.prod.google.com ([2002:a17:903:13c8:b0:212:472e:4a64]) (user=jstultz job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:cf01:b0:20c:e8df:2516 with SMTP id d9443c01a7336-2129f81e889mr179409315ad.42.1732564329853; Mon, 25 Nov 2024 11:52:09 -0800 (PST) Date: Mon, 25 Nov 2024 11:51:56 -0800 In-Reply-To: <20241125195204.2374458-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241125195204.2374458-1-jstultz@google.com> X-Mailer: git-send-email 2.47.0.371.ga323438b13-goog Message-ID: <20241125195204.2374458-3-jstultz@google.com> Subject: [RFC][PATCH v14 2/7] locking/mutex: Rework task_struct::blocked_on From: John Stultz To: LKML Cc: Peter Zijlstra , Joel Fernandes , Qais Yousef , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Zimuzo Ezeozue , Mel Gorman , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , kernel-team@android.com, "Connor O'Brien" , John Stultz Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Peter Zijlstra Track the blocked-on relation for mutexes, to allow following this relation at schedule time. task | blocked-on v mutex | owner v task Also add a blocked_on_state value so we can distinguish when a task is blocked_on a mutex, but is either blocked, waking up, or runnable (such that it can try to acquire the lock its blocked on). This avoids some of the subtle & racy games where the blocked_on state gets cleared, only to have it re-added by the mutex_lock_slowpath call when it tries to acquire the lock on wakeup Also add blocked_lock to the task_struct so we can safely serialize the blocked-on state. Finally add wrappers that are useful to provide correctness checks. Folded in from a patch by: Valentin Schneider This all will be used for tracking blocked-task/mutex chains with the prox-execution patch in a similar fashion to how priority inheritance is done with rt_mutexes. Cc: Joel Fernandes Cc: Qais Yousef Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Steven Rostedt Cc: Ben Segall Cc: Zimuzo Ezeozue Cc: Mel Gorman Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Cc: "Paul E. McKenney" Cc: Metin Kaya Cc: Xuewen Yan Cc: K Prateek Nayak Cc: Thomas Gleixner Cc: Daniel Lezcano Cc: kernel-team@android.com Signed-off-by: Peter Zijlstra (Intel) [minor changes while rebasing] Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Connor O'Brien [jstultz: Fix blocked_on tracking in __mutex_lock_common in error paths] Signed-off-by: John Stultz --- v2: * Fixed blocked_on tracking in error paths that was causing crashes v4: * Ensure we clear blocked_on when waking ww_mutexes to die or wound. This is critical so we don't get circular blocked_on relationships that can't be resolved. v5: * Fix potential bug where the skip_wait path might clear blocked_on when that path never set it * Slight tweaks to where we set blocked_on to make it consistent, along with extra WARN_ON correctness checking * Minor comment changes v7: * Minor commit message change suggested by Metin Kaya * Fix WARN_ON conditionals in unlock path (as blocked_on might already be cleared), found while looking at issue Metin Kaya raised. * Minor tweaks to be consistent in what we do under the blocked_on lock, also tweaked variable name to avoid confusion with label, and comment typos, as suggested by Metin Kaya * Minor tweak for CONFIG_SCHED_PROXY_EXEC name change * Moved unused block of code to later in the series, as suggested by Metin Kaya * Switch to a tri-state to be able to distinguish from waking and runnable so we can later safely do return migration from ttwu * Folded together with related blocked_on changes v8: * Fix issue leaving task BO_BLOCKED when calling into optimistic spinning path. * Include helper to better handle BO_BLOCKED->BO_WAKING transitions v9: * Typo fixup pointed out by Metin * Cleanup BO_WAKING->BO_RUNNABLE transitions for the !proxy case * Many cleanups and simplifications suggested by Metin v11: * Whitespace fixup pointed out by Metin v13: * Refactor set_blocked_on helpers clean things up a bit v14: * Small build fixup with PREEMPT_RT --- include/linux/sched.h | 66 ++++++++++++++++++++++++++++++++---- init/init_task.c | 1 + kernel/fork.c | 4 +-- kernel/locking/mutex-debug.c | 9 ++--- kernel/locking/mutex.c | 40 ++++++++++++++++++---- kernel/locking/ww_mutex.h | 24 +++++++++++-- kernel/sched/core.c | 1 + 7 files changed, 125 insertions(+), 20 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 24e338ac34d7b..0ad8033f8c2b9 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -775,6 +776,12 @@ struct kmap_ctrl { #endif }; =20 +enum blocked_on_state { + BO_RUNNABLE, + BO_BLOCKED, + BO_WAKING, +}; + struct task_struct { #ifdef CONFIG_THREAD_INFO_IN_TASK /* @@ -1195,10 +1202,9 @@ struct task_struct { struct rt_mutex_waiter *pi_blocked_on; #endif =20 -#ifdef CONFIG_DEBUG_MUTEXES - /* Mutex deadlock detection: */ - struct mutex_waiter *blocked_on; -#endif + enum blocked_on_state blocked_on_state; + struct mutex *blocked_on; /* lock we're blocked on */ + raw_spinlock_t blocked_lock; =20 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP int non_block_count; @@ -2118,6 +2124,56 @@ extern int __cond_resched_rwlock_write(rwlock_t *loc= k); __cond_resched_rwlock_write(lock); \ }) =20 +static inline void __set_blocked_on_runnable(struct task_struct *p) +{ + lockdep_assert_held(&p->blocked_lock); + + if (p->blocked_on_state =3D=3D BO_WAKING) + p->blocked_on_state =3D BO_RUNNABLE; +} + +static inline void set_blocked_on_runnable(struct task_struct *p) +{ + unsigned long flags; + + if (!sched_proxy_exec()) + return; + + raw_spin_lock_irqsave(&p->blocked_lock, flags); + __set_blocked_on_runnable(p); + raw_spin_unlock_irqrestore(&p->blocked_lock, flags); +} + +static inline void set_blocked_on_waking(struct task_struct *p) +{ + lockdep_assert_held(&p->blocked_lock); + + if (p->blocked_on_state =3D=3D BO_BLOCKED) + p->blocked_on_state =3D BO_WAKING; +} + +static inline void set_task_blocked_on(struct task_struct *p, struct mutex= *m) +{ + lockdep_assert_held(&p->blocked_lock); + + /* + * Check we are clearing values to NULL or setting NULL + * to values to ensure we don't overwrite existing mutex + * values or clear already cleared values + */ + WARN_ON((!m && !p->blocked_on) || (m && p->blocked_on)); + + p->blocked_on =3D m; + p->blocked_on_state =3D m ? BO_BLOCKED : BO_RUNNABLE; +} + +static inline struct mutex *get_task_blocked_on(struct task_struct *p) +{ + lockdep_assert_held(&p->blocked_lock); + + return p->blocked_on; +} + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); @@ -2157,8 +2213,6 @@ extern bool sched_task_on_rq(struct task_struct *p); extern unsigned long get_wchan(struct task_struct *p); extern struct task_struct *cpu_curr_snapshot(int cpu); =20 -#include - /* * In order to reduce various lock holder preemption latencies provide an * interface to see if a vCPU is currently running or not. diff --git a/init/init_task.c b/init/init_task.c index e557f622bd906..7e29d86153d9f 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -140,6 +140,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = =3D { .journal_info =3D NULL, INIT_CPU_TIMERS(init_task) .pi_lock =3D __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock), + .blocked_lock =3D __RAW_SPIN_LOCK_UNLOCKED(init_task.blocked_lock), .timer_slack_ns =3D 50000, /* 50 usec default slack */ .thread_pid =3D &init_struct_pid, .thread_node =3D LIST_HEAD_INIT(init_signals.thread_head), diff --git a/kernel/fork.c b/kernel/fork.c index f253e81d0c28e..160bead843afb 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2231,6 +2231,7 @@ __latent_entropy struct task_struct *copy_process( ftrace_graph_init_task(p); =20 rt_mutex_init_task(p); + raw_spin_lock_init(&p->blocked_lock); =20 lockdep_assert_irqs_enabled(); #ifdef CONFIG_PROVE_LOCKING @@ -2329,9 +2330,8 @@ __latent_entropy struct task_struct *copy_process( lockdep_init_task(p); #endif =20 -#ifdef CONFIG_DEBUG_MUTEXES + p->blocked_on_state =3D BO_RUNNABLE; p->blocked_on =3D NULL; /* not blocked yet */ -#endif #ifdef CONFIG_BCACHE p->sequential_io =3D 0; p->sequential_io_avg =3D 0; diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index 6e6f6071cfa27..1d8cff71f65e1 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -53,17 +53,18 @@ void debug_mutex_add_waiter(struct mutex *lock, struct = mutex_waiter *waiter, { lockdep_assert_held(&lock->wait_lock); =20 - /* Mark the current thread as blocked on the lock: */ - task->blocked_on =3D waiter; + /* Current thread can't be already blocked (since it's executing!) */ + DEBUG_LOCKS_WARN_ON(get_task_blocked_on(task)); } =20 void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *wa= iter, struct task_struct *task) { + struct mutex *blocked_on =3D get_task_blocked_on(task); + DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list)); DEBUG_LOCKS_WARN_ON(waiter->task !=3D task); - DEBUG_LOCKS_WARN_ON(task->blocked_on !=3D waiter); - task->blocked_on =3D NULL; + DEBUG_LOCKS_WARN_ON(blocked_on && blocked_on !=3D lock); =20 INIT_LIST_HEAD(&waiter->list); waiter->task =3D NULL; diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 3302e52f0c967..8f5d3fe6c1029 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -597,6 +597,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas } =20 raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); /* * After waiting to acquire the wait_lock, try again. */ @@ -627,6 +628,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err_early_kill; } =20 + set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -639,7 +641,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas * the handoff. */ if (__mutex_trylock(lock)) - goto acquired; + break; /* acquired */; =20 /* * Check for signals and kill conditions while holding @@ -657,6 +659,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err; } =20 + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); /* Make sure we do wakeups before calling schedule */ wake_up_q(&wake_q); @@ -666,6 +669,13 @@ __mutex_lock_common(struct mutex *lock, unsigned int s= tate, unsigned int subclas =20 first =3D __mutex_waiter_is_first(lock, &waiter); =20 + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); + + /* + * Re-set blocked_on_state as unlock path set it to WAKING/RUNNABLE + */ + current->blocked_on_state =3D BO_BLOCKED; set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -676,16 +686,26 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas break; =20 if (first) { + bool opt_acquired; + + /* + * mutex_optimistic_spin() can schedule, so we need to + * release these locks before calling it. + */ + current->blocked_on_state =3D BO_RUNNABLE; + raw_spin_unlock(¤t->blocked_lock); + raw_spin_unlock_irqrestore(&lock->wait_lock, flags); trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); - if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) + opt_acquired =3D mutex_optimistic_spin(lock, ww_ctx, &waiter); + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); + current->blocked_on_state =3D BO_BLOCKED; + if (opt_acquired) break; trace_contention_begin(lock, LCB_F_MUTEX); } - - raw_spin_lock_irqsave(&lock->wait_lock, flags); } - raw_spin_lock_irqsave(&lock->wait_lock, flags); -acquired: + set_task_blocked_on(current, NULL); __set_current_state(TASK_RUNNING); =20 if (ww_ctx) { @@ -710,16 +730,20 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas if (ww_ctx) ww_mutex_lock_acquired(ww, ww_ctx); =20 + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); wake_up_q(&wake_q); preempt_enable(); return 0; =20 err: + set_task_blocked_on(current, NULL); __set_current_state(TASK_RUNNING); __mutex_remove_waiter(lock, &waiter); err_early_kill: + WARN_ON(get_task_blocked_on(current)); trace_contention_end(lock, ret); + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); debug_mutex_free_waiter(&waiter); mutex_release(&lock->dep_map, ip); @@ -928,8 +952,12 @@ static noinline void __sched __mutex_unlock_slowpath(s= truct mutex *lock, unsigne =20 next =3D waiter->task; =20 + raw_spin_lock(&next->blocked_lock); debug_mutex_wake_waiter(lock, waiter); + WARN_ON(get_task_blocked_on(next) !=3D lock); + set_blocked_on_waking(next); wake_q_add(&wake_q, next); + raw_spin_unlock(&next->blocked_lock); } =20 if (owner & MUTEX_FLAG_HANDOFF) diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 37f025a096c9d..d9ff2022eef6f 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -281,10 +281,21 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITE= R *waiter, return false; =20 if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)= ) { + /* nested as we should hold current->blocked_lock already */ + raw_spin_lock_nested(&waiter->task->blocked_lock, SINGLE_DEPTH_NESTING); #ifndef WW_RT debug_mutex_wake_waiter(lock, waiter); + /* + * When waking up the task to die, be sure to set the + * blocked_on_state to WAKING. Otherwise we can see + * circular blocked_on relationships that can't + * resolve. + */ + WARN_ON(get_task_blocked_on(waiter->task) !=3D lock); #endif + set_blocked_on_waking(waiter->task); wake_q_add(wake_q, waiter->task); + raw_spin_unlock(&waiter->task->blocked_lock); } =20 return true; @@ -331,9 +342,18 @@ static bool __ww_mutex_wound(struct MUTEX *lock, * it's wounded in __ww_mutex_check_kill() or has a * wakeup pending to re-read the wounded state. */ - if (owner !=3D current) + if (owner !=3D current) { + /* nested as we should hold current->blocked_lock already */ + raw_spin_lock_nested(&owner->blocked_lock, SINGLE_DEPTH_NESTING); + /* + * When waking up the task to wound, be sure to set the + * blocked_on_state flag. Otherwise we can see circular + * blocked_on relationships that can't resolve. + */ + set_blocked_on_waking(owner); wake_q_add(wake_q, owner); - + raw_spin_unlock(&owner->blocked_lock); + } return true; } =20 diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d712e177d3b75..f8714050b6d0d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4350,6 +4350,7 @@ int try_to_wake_up(struct task_struct *p, unsigned in= t state, int wake_flags) ttwu_queue(p, cpu, wake_flags); } out: + set_blocked_on_runnable(p); if (success) ttwu_stat(p, task_cpu(p), wake_flags); =20 --=20 2.47.0.371.ga323438b13-goog