From nobody Fri Dec 19 14:13:28 2025 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 F1D2CAD2E for ; Wed, 20 Dec 2023 00:19:12 +0000 (UTC) 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="N1oZrSP2" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-5ca5b61c841so2045759a12.3 for ; Tue, 19 Dec 2023 16:19:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1703031552; x=1703636352; 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=sqfwQXYrs0dla1Ln+uFCJhXbwMO3b1s4DQoQ/IjlTnQ=; b=N1oZrSP2R+R2WerPrKUNgaQ9//qFIntPz3SemUYd3IsVr7A+oTP/IdePvYsYdyyXZQ AX+MoE9gniRQtLGneHUfadpYqcbJGytt3OsIu6lu3SDAvhR4I32w7RYfRDvmY8pFpNkW cIVyFy3CTXFp+b2QmX8VDdPqeHtvNVInGPCe17k3gEF+8FnkjqNfv3gQruE7oNb5+Sh/ jGRoBEEHZvMWzT6CwwZBQr1ePKowQatHu9pg+mygLBV2hCz3R3wKAlsye3evAzElyIfP H90ojml5Xh1Z9Z/2fQ2xK8iXGqVz47UksLxD6tiLe+wWu9tCv0KNLyMc+272geAE8POD CPfg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1703031552; x=1703636352; 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=sqfwQXYrs0dla1Ln+uFCJhXbwMO3b1s4DQoQ/IjlTnQ=; b=SA13avKNdzLQy/ya57opfWxnMSaKB5AKzTzfLqkij24vGhLaLv4XXF2nXvbIZCQYMf cTr/AM8KlbtN4+zQUfeb/j2Lpyb2ecrdXI1fr1heIb1NgRNN8/1weGajCWzaV7xRnCpj dpDVNS6xBJ0pfGsLyfqlX4IzHSUk6B5O6ICvNZ0fmLu1zvT4GrEMPNFhtBzBW7u/8dqT E3qhxJAaoE63s1MMZBioa5Tqie6la4PFhp6CiTYkMcs7FuedHtdgwRHAZOsbxIhAU7M0 JbOzfiSs0NVgDZLY++u4wCGbIXpHCFZnxhThmlDb9fUFDT45+nKEDjbcpuggmsOnwsOL G4hQ== X-Gm-Message-State: AOJu0Ywzw1L7fBB2kWzlHePyrjfFqmG1n/ZXsrH87EN4yn9qYmHuAZBy c069+r5G9HxyUt30/ge7P4uXG7pjiY5ZhrGVFpVuT1DgjkIcv39BuhHUgDkWU+z8SpNtJ4fHDSU GrR69TRlF4JfymYge81TvfanWx2pzVVNZwfGMGDHB9y0CITYERcI6Yyofa6qaJPOm5MDwmg0= X-Google-Smtp-Source: AGHT+IGh6Z6BHPJUwvSt9BuByFFALZMShZzYYkaVsrXYhrA6wg1FQNteSkJIydioVggPy4D54upfw0/x8kyV X-Received: from jstultz-noogler2.c.googlers.com ([fda3:e722:ac3:cc00:24:72f4:c0a8:600]) (user=jstultz job=sendgmr) by 2002:a05:6a02:68a:b0:5cd:a34c:f9db with SMTP id ca10-20020a056a02068a00b005cda34cf9dbmr23155pgb.10.1703031551064; Tue, 19 Dec 2023 16:19:11 -0800 (PST) Date: Tue, 19 Dec 2023 16:18:16 -0800 In-Reply-To: <20231220001856.3710363-1-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20231220001856.3710363-1-jstultz@google.com> X-Mailer: git-send-email 2.43.0.472.g3155946c3a-goog Message-ID: <20231220001856.3710363-6-jstultz@google.com> Subject: [PATCH v7 05/23] 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 , Youssef Esmat , Mel Gorman , Daniel Bristot de Oliveira , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , 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 adds a blocked_on_state value so we can distinguqish when a task is blocked_on a mutex, but is either blocked, waking up, or runnable (such that it can try to aquire 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 aquire the lock on wakeup Also adds blocked_lock to the task_struct so we can safely serialize the blocked-on state. Finally adds 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 inheritence 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: Youssef Esmat Cc: Mel Gorman Cc: Daniel Bristot de Oliveira 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: 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 ciruclar 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 --- include/linux/sched.h | 40 ++++++++++++++++++++++++++++++++---- init/init_task.c | 1 + kernel/fork.c | 4 ++-- kernel/locking/mutex-debug.c | 9 ++++---- kernel/locking/mutex.c | 35 +++++++++++++++++++++++++++---- kernel/locking/ww_mutex.h | 24 ++++++++++++++++++++-- kernel/sched/core.c | 6 ++++++ 7 files changed, 103 insertions(+), 16 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 1e80c330f755..bfe8670f99a1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -743,6 +743,12 @@ struct kmap_ctrl { #endif }; =20 +enum blocked_on_state { + BO_RUNNABLE, + BO_BLOCKED, + BO_WAKING, +}; + struct task_struct { #ifdef CONFIG_THREAD_INFO_IN_TASK /* @@ -1149,10 +1155,9 @@ 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; @@ -2258,6 +2263,33 @@ static inline int rwlock_needbreak(rwlock_t *lock) #endif } =20 +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 exisiting 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 inline struct mutex *get_task_blocked_on_once(struct task_struct *p) +{ + return READ_ONCE(p->blocked_on); +} + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); diff --git a/init/init_task.c b/init/init_task.c index 5727d42149c3..0c31d7d7c7a9 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -131,6 +131,7 @@ struct task_struct init_task .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 10917c3e1f03..b3ba3d22d8b2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2358,6 +2358,7 @@ __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 @@ -2456,9 +2457,8 @@ __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 bc8abb8549d2..1eedf7c60c00 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -52,17 +52,18 @@ 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_once(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 543774506fdb..6084470773f6 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -592,6 +592,7 @@ __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. */ @@ -622,6 +623,7 @@ __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 (;;) { @@ -652,6 +654,7 @@ __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 */ if (!wake_q_empty(&wake_q)) { @@ -662,6 +665,13 @@ __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 @@ -672,16 +682,25 @@ __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. + */ + 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); + 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) { @@ -706,16 +725,20 @@ __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(current->blocked_on); 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); @@ -925,8 +948,12 @@ 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(next->blocked_on !=3D lock); + next->blocked_on_state =3D BO_WAKING; 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 9facc0ddfdd3..8dd21ff5eee0 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); #endif + /* + * 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(waiter->task->blocked_on !=3D lock); + waiter->task->blocked_on_state =3D BO_WAKING; 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. + */ + owner->blocked_on_state =3D BO_WAKING; 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 a708d225c28e..4e46189d545d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4195,6 +4195,7 @@ bool ttwu_state_match(struct task_struct *p, unsigned= int state, int *success) int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_fla= gs) { guard(preempt)(); + unsigned long flags; int cpu, success =3D 0; =20 if (p =3D=3D current) { @@ -4341,6 +4342,11 @@ int try_to_wake_up(struct task_struct *p, unsigned i= nt state, int wake_flags) =20 ttwu_queue(p, cpu, wake_flags); } + /* XXX can we do something better here for !CONFIG_SCHED_PROXY_EXEC case = */ + raw_spin_lock_irqsave(&p->blocked_lock, flags); + if (p->blocked_on_state =3D=3D BO_WAKING) + p->blocked_on_state =3D BO_RUNNABLE; + raw_spin_unlock_irqrestore(&p->blocked_lock, flags); out: if (success) ttwu_stat(p, task_cpu(p), wake_flags); --=20 2.43.0.472.g3155946c3a-goog