From nobody Tue Oct 7 00:21:15 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 A18D22F3643; Wed, 16 Jul 2025 10:19:11 +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=1752661153; cv=none; b=MyMLagCmSSWQ5n0cCKnHBfg+mowgbn3bsj1+vMu5N5mqorXNNJ8C89wK+t+tPtea91xuYnGHieRGlRo8FAtjbAYc1wseDUYwONSmtfQx2EA9rum6tXVg0Feqj3PdCh1O/ZTTAzZ7ezDHtHd1NWCspuQ5w5cc1gbzollBYgpsa0c= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752661153; c=relaxed/simple; bh=dWx3lE0Oluia463vcQ6dFzI2NW8+/vOygcPeDt62Dn8=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=UQWnu2l572pmBEaAI79xgzzKj3OJBVETBvvcrlD7GwaV4flO00LW9Kzq3D56t80tZjFjJY9thr7DkTUxioZ7I0VAcjO+CaDXB+68DckTV3rcDvyCJtRVPBQcGhiMQvFabajhbmhur8d6Sot3k+Oqhn8vOsonSnp5Mb75O1M84XY= 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=xiypQgZo; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=UIAP95Cg; 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="xiypQgZo"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="UIAP95Cg" Date: Wed, 16 Jul 2025 10:19:06 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1752661148; 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=i5P0rcU56d3KD5w0GfT1aGVYBx5dqRenk94Cnj0Egis=; b=xiypQgZogezcAiEvsQt5xtN88DkK1fBKhIeI4B/LLxq5UKrsutxSxP/vsrKR8jVZCeGU+L 0EjNPT545Fzp/iXwW02CQ6bkxCPEIwOx/3BwiRKrBfwj7xYoVaKTw/7BNBD1TcY1pW5+jc 4DdR2/3LJjILKoybbiavSFgmI6LnfjXT7YJNjk9cIJc6Ewb06i/nsPQX9ulnbsDctt0FbN uqqhHkOo3H2IvkNVUMejphBgajf7Om5kjY3l6V7ZdL7ioyj5HoNmq6CsyMNQnGehtLSAW8 Zemr1WpWCYoSf6QYNsfQl3NhPQvWh3XdgewcRy+fh6EQHblEfsCbUR43e698+Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1752661148; 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=i5P0rcU56d3KD5w0GfT1aGVYBx5dqRenk94Cnj0Egis=; b=UIAP95CgTB14VUKxqVHQshERk0OHPFrTsK8RWD7uBSQSCFSzwQ9a1SZNFarnMXt55C+swA EmSI1dnxARltAWAg== From: "tip-bot2 for Luis Claudio R. Goncalves" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched: Do not call __put_task_struct() on rt if pi_blocked_on is set Cc: Crystal Wood , "Luis Claudio R. Goncalves" , "Peter Zijlstra (Intel)" , Wander Lairson Costa , Valentin Schneider , Sebastian Andrzej Siewior , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <175266114691.406.7896002779139561970.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: 8671bad873ebeb082afcf7b4501395c374da6023 Gitweb: https://git.kernel.org/tip/8671bad873ebeb082afcf7b4501395c37= 4da6023 Author: Luis Claudio R. Goncalves AuthorDate: Mon, 07 Jul 2025 11:03:59 -03:00 Committer: Peter Zijlstra CommitterDate: Mon, 14 Jul 2025 17:16:33 +02:00 sched: Do not call __put_task_struct() on rt if pi_blocked_on is set With PREEMPT_RT enabled, some of the calls to put_task_struct() coming from rt_mutex_adjust_prio_chain() could happen in preemptible context and with a mutex enqueued. That could lead to this sequence: rt_mutex_adjust_prio_chain() put_task_struct() __put_task_struct() sched_ext_free() spin_lock_irqsave() rtlock_lock() ---> TRIGGERS lockdep_assert(!current->pi_blocked_o= n); This is not a SCHED_EXT bug. The first cleanup function called by __put_task_struct() is sched_ext_free() and it happens to take a (RT) spin_lock, which in the scenario described above, would trigger the lockdep assertion of "!current->pi_blocked_on". Crystal Wood was able to identify the problem as __put_task_struct() being called during rt_mutex_adjust_prio_chain(), in the context of a process with a mutex enqueued. Instead of adding more complex conditions to decide when to directly call __put_task_struct() and when to defer the call, unconditionally resort to the deferred call on PREEMPT_RT to simplify the code. Fixes: 893cdaaa3977 ("sched: avoid false lockdep splat in put_task_struct()= ") Suggested-by: Crystal Wood Signed-off-by: Luis Claudio R. Goncalves Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Wander Lairson Costa Reviewed-by: Valentin Schneider Reviewed-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/aGvTz5VaPFyj0pBV@uudg.org --- include/linux/sched/task.h | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index c517dbc..ea41795 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -131,24 +131,17 @@ static inline void put_task_struct(struct task_struct= *t) return; =20 /* - * In !RT, it is always safe to call __put_task_struct(). - * Under RT, we can only call it in preemptible context. - */ - if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) { - static DEFINE_WAIT_OVERRIDE_MAP(put_task_map, LD_WAIT_SLEEP); - - lock_map_acquire_try(&put_task_map); - __put_task_struct(t); - lock_map_release(&put_task_map); - return; - } - - /* - * under PREEMPT_RT, we can't call put_task_struct + * Under PREEMPT_RT, we can't call __put_task_struct * in atomic context because it will indirectly - * acquire sleeping locks. + * acquire sleeping locks. The same is true if the + * current process has a mutex enqueued (blocked on + * a PI chain). + * + * In !RT, it is always safe to call __put_task_struct(). + * Though, in order to simplify the code, resort to the + * deferred call too. * - * call_rcu() will schedule delayed_put_task_struct_rcu() + * call_rcu() will schedule __put_task_struct_rcu_cb() * to be called in process context. * * __put_task_struct() is called when @@ -161,7 +154,7 @@ static inline void put_task_struct(struct task_struct *= t) * * delayed_free_task() also uses ->rcu, but it is only called * when it fails to fork a process. Therefore, there is no - * way it can conflict with put_task_struct(). + * way it can conflict with __put_task_struct(). */ call_rcu(&t->rcu, __put_task_struct_rcu_cb); }