From nobody Tue Oct 7 00:21:13 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 35E732F4338; Wed, 16 Jul 2025 10:19:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752661158; cv=none; b=SDEH6lttoO2hVMFcTEO+Ujn55SpjrpkgtkX5oSYwWq+M4LclQCbxhrv13+g9v4WyK5giDyFq6Kahb10KDK7kw4Nhraac7PK5LQSiV5cEX40RhOExTusDcPdZWCOYFS+X3kx6TLCJOjOxlzayWOzQRSVYgr7Bti7n/gfjU73o6mI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752661158; c=relaxed/simple; bh=ST9ya2/jDiC4Hmwe5bCkQ1jpCEFOQr5oA3c4MYBaTUs=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=sj2TDrH7n6yM1V0XVTJLylX3G+Y9fqDSA2VoQnatp0v/MMZGu/l+n4LKnmtlOxeb9bgoUHkTVDR+oO3gQRzXKCXQBxAIilQ9ZTJiBAClRH+C2LUWSuvYgJYpRW6ZaAfWp37NPXkrLcgdcoVLhjCRKZmtCHwWa2nTwCU+vi6LOnQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=Uwe462pC; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=U3SIVWqc; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="Uwe462pC"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="U3SIVWqc" Date: Wed, 16 Jul 2025 10:19:13 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1752661154; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8xCVeX3e/yVgRACkSNDxQZIA9E222FHkideCjsLa6gQ=; b=Uwe462pCN3ehYe8MUBXocNvNaI45TgUYdNa/DdvTFyr8wG7I6SrT18VPtXJsx49rXuBZcH j3HcJqHcy1dzzpvYAGuyN/d8b9SvpWHQomamo+qLPZuW1v0Nbm3c8dbuE+lu9bFPq4xg7r TVSkgLTWSzDHlxNOfl/9CmNvSvZgiiQ2fc7+Hky90KCShAwTevjp+bLsZnGQ9chdb0iwwe NVPvLfvsjKrGBmEEZjgYBKpaIsk4CrKa9gruQIrWS+csuhz96oFVQWA8+Sn5d5oty0OWwg TnMFx7y8sGBuSf3jsmDxCJMuDoVJrGM29QSocAvJK9Y7/3WJaqAXAYH8VN3vnQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1752661154; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=8xCVeX3e/yVgRACkSNDxQZIA9E222FHkideCjsLa6gQ=; b=U3SIVWqcuTKBH4lsqrDM4YH0U9Le6KWrQcTUq/jVAlMKXAB6A9Nks/g7B1AfYgkoYRvUAX oPFxjFyUtM4QszAQ== From: "tip-bot2 for Peter Zijlstra" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] locking/mutex: Rework task_struct::blocked_on Cc: "Peter Zijlstra (Intel)" , Juri Lelli , "Connor O'Brien" , John Stultz , K Prateek Nayak , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20250712033407.2383110-3-jstultz@google.com> References: <20250712033407.2383110-3-jstultz@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <175266115340.406.7737633482808574220.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the sched/core branch of tip: Commit-ID: 44e4e0297c3c01987399bb9973f4d22a096a62c2 Gitweb: https://git.kernel.org/tip/44e4e0297c3c01987399bb9973f4d22a0= 96a62c2 Author: Peter Zijlstra AuthorDate: Sat, 12 Jul 2025 03:33:43=20 Committer: Peter Zijlstra CommitterDate: Mon, 14 Jul 2025 17:16:31 +02:00 locking/mutex: Rework task_struct::blocked_on Track the blocked-on relation for mutexes, to allow following this relation at schedule time. task | blocked-on v mutex | owner v task 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. For serialization, blocked-on is only set by the task itself (current). And both when setting or clearing (potentially by others), is done while holding the mutex::wait_lock. [minor changes while rebasing] [jstultz: Fix blocked_on tracking in __mutex_lock_common in error paths] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Juri Lelli Signed-off-by: Connor O'Brien Signed-off-by: John Stultz Signed-off-by: Peter Zijlstra (Intel) Tested-by: K Prateek Nayak Link: https://lkml.kernel.org/r/20250712033407.2383110-3-jstultz@google.com --- include/linux/sched.h | 5 +---- kernel/fork.c | 3 +-- kernel/locking/mutex-debug.c | 9 +++++---- kernel/locking/mutex.c | 22 ++++++++++++++++++++++ kernel/locking/ww_mutex.h | 18 ++++++++++++++++-- 5 files changed, 45 insertions(+), 12 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index f225b6b..33ad240 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1230,10 +1230,7 @@ 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 + struct mutex *blocked_on; /* lock we're blocked on */ =20 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER /* diff --git a/kernel/fork.c b/kernel/fork.c index 1ee8eb1..5f87f05 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2123,9 +2123,8 @@ __latent_entropy struct task_struct *copy_process( lockdep_init_task(p); #endif =20 -#ifdef CONFIG_DEBUG_MUTEXES 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 6e6f607..758b7a6 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(task->blocked_on); } =20 void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *wa= iter, struct task_struct *task) { + struct mutex *blocked_on =3D READ_ONCE(task->blocked_on); + 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 a39eccc..e2f5986 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -644,6 +644,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err_early_kill; } =20 + WARN_ON(current->blocked_on); + current->blocked_on =3D lock; set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -680,6 +682,12 @@ __mutex_lock_common(struct mutex *lock, unsigned int s= tate, unsigned int subclas =20 first =3D __mutex_waiter_is_first(lock, &waiter); =20 + /* + * As we likely have been woken up by task + * that has cleared our blocked_on state, re-set + * it to the lock we are trying to aquire. + */ + current->blocked_on =3D lock; set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -691,8 +699,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int s= tate, unsigned int subclas =20 if (first) { trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); + /* clear blocked_on as mutex_optimistic_spin may schedule() */ + current->blocked_on =3D NULL; if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) break; + current->blocked_on =3D lock; trace_contention_begin(lock, LCB_F_MUTEX); } =20 @@ -700,6 +711,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas } raw_spin_lock_irqsave(&lock->wait_lock, flags); acquired: + current->blocked_on =3D NULL; __set_current_state(TASK_RUNNING); =20 if (ww_ctx) { @@ -729,9 +741,11 @@ skip_wait: return 0; =20 err: + current->blocked_on =3D 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_irqrestore_wake(&lock->wait_lock, flags, &wake_q); debug_mutex_free_waiter(&waiter); @@ -942,6 +956,14 @@ static noinline void __sched __mutex_unlock_slowpath(s= truct mutex *lock, unsigne next =3D waiter->task; =20 debug_mutex_wake_waiter(lock, waiter); + /* + * Unlock wakeups can be happening in parallel + * (when optimistic spinners steal and release + * the lock), so blocked_on may already be + * cleared here. + */ + WARN_ON(next->blocked_on && next->blocked_on !=3D lock); + next->blocked_on =3D NULL; wake_q_add(&wake_q, next); } =20 diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 37f025a..45fe05e 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -283,7 +283,15 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER= *waiter, if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)= ) { #ifndef WW_RT debug_mutex_wake_waiter(lock, waiter); + /* + * When waking up the task to die, be sure to clear the + * blocked_on pointer. Otherwise we can see circular + * blocked_on relationships that can't resolve. + */ + WARN_ON(waiter->task->blocked_on && + waiter->task->blocked_on !=3D lock); #endif + waiter->task->blocked_on =3D NULL; wake_q_add(wake_q, waiter->task); } =20 @@ -331,9 +339,15 @@ 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) { + /* + * When waking up the task to wound, be sure to clear the + * blocked_on pointer. Otherwise we can see circular + * blocked_on relationships that can't resolve. + */ + owner->blocked_on =3D NULL; wake_q_add(wake_q, owner); - + } return true; }