From nobody Thu Nov 28 09:52:49 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1C4F91D079B; Wed, 2 Oct 2024 14:57:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881068; cv=none; b=ZpZVFccqSDJ3h5nmo3l/4F0ZFLZ0LAl6MfSYTHYRF+AF5Xau/YASRUDYb7bbZiNUUhKdrRxXZysvvmhq4nmwNIjQFV/zrZ/BhN8miNfb6wJeH3ff+D+t6m4nKS3Qzi7D5kSwWy7ErbQpl0oasJ2ZQHQQEH+I8o4Nj3Qn7mZI+h8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881068; c=relaxed/simple; bh=52YRPDjGp4dDviquEXrrl2kjbqpQryVts8kljcTPeDY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hzRGxVNPjSSXvmenqZOIBt9vW2WSZ1h0KtxzlBKpNOkXASY53nnFaRP8SrGzvZznA+HcCVJELxKnbUG2spzXmnEvIiQe3c+b7tWqRb1h8XqUr3vyNNRurugvD750sjfu5Z+o2cyg36SpNrYxl7rWPE1GY05zrQrA+wQV1hGta9w= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=F75B7Wsv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="F75B7Wsv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3FB1C4CEC2; Wed, 2 Oct 2024 14:57:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727881067; bh=52YRPDjGp4dDviquEXrrl2kjbqpQryVts8kljcTPeDY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=F75B7WsvBbvuxc7fsu+By/22DRQxkIj+tWtpyw0rstH6Zr3zHNGV9P2WpR1tPS9Pg wX0aTUxv2tqrMA6ODjShbWOCL9IK0IzmlpiBOZpiQrOO1tnQc7e5P4apJk5HaFxhXn TAuv7M37lNIni9xqcaFW5ZZ1YsrygDYRNI69oZe3MyqVp+beYogl0UGsSjfG0PN5pg x+IPQwsW+cqGnQMQvKjX5A+O/xpcdfYDxZBM10K39BqaC4Ia2j1YqRfBsIEKdfagNT 7JGDSbaZSIBCX+sGXxS5E3NAf9cbQ2/nl+Pd9cVSRSMofSthj9Ig/9fF7D+NfB5LbL RwRcag8PXKBjQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Boqun Feng , Joel Fernandes , Neeraj Upadhyay , "Paul E . McKenney" , Uladzislau Rezki , Zqiang , rcu Subject: [PATCH 1/3] rcu/nocb: Use switch/case on NOCB timer state machine Date: Wed, 2 Oct 2024 16:57:36 +0200 Message-ID: <20241002145738.38226-2-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20241002145738.38226-1-frederic@kernel.org> References: <20241002145738.38226-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" It's more convenient to benefit from the fallthrough feature of switch / case to handle the timer state machine. Also a new state is about to be added that will take advantage of it. No intended functional change. Signed-off-by: Frederic Weisbecker --- kernel/rcu/tree_nocb.h | 33 +++++++++++++++++++++++---------- 1 file changed, 23 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 97b99cd06923..2fb803f863da 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -271,22 +271,35 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, = int waketype, =20 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); =20 - /* - * Bypass wakeup overrides previous deferments. In case of - * callback storms, no need to wake up too early. - */ - if (waketype =3D=3D RCU_NOCB_WAKE_LAZY && - rdp->nocb_defer_wakeup =3D=3D RCU_NOCB_WAKE_NOT) { - mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush()); - WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); - } else if (waketype =3D=3D RCU_NOCB_WAKE_BYPASS) { + switch (waketype) { + case RCU_NOCB_WAKE_BYPASS: + /* + * Bypass wakeup overrides previous deferments. In case of + * callback storms, no need to wake up too early. + */ mod_timer(&rdp_gp->nocb_timer, jiffies + 2); WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); - } else { + break; + case RCU_NOCB_WAKE_LAZY: + if (rdp->nocb_defer_wakeup =3D=3D RCU_NOCB_WAKE_NOT) { + mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush()); + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + } + /* + * If the timer is already armed, a non-lazy enqueue may have happened + * in-between. Don't delay it and fall-through. + */ + break; + case RCU_NOCB_WAKE: + fallthrough; + case RCU_NOCB_WAKE_FORCE: if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE) mod_timer(&rdp_gp->nocb_timer, jiffies + 1); if (rdp_gp->nocb_defer_wakeup < waketype) WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + break; + default: + WARN_ON_ONCE(1); } =20 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); --=20 2.46.0 From nobody Thu Nov 28 09:52:49 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 535328F40; Wed, 2 Oct 2024 14:57:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881070; cv=none; b=T8WY5LmtG2Uxpjue1jhemzIMygQZwR+whCEdH3yLiellB2Q3T7JkxJl9QLVF6ejDZ4X/j0ltDV0bvwqBDdk1P1y0GHAy3Hhj7gtqIgdWnjy+izDOyni6n3D1SYK41AronOob83IwZGmdzh6qRJUvet3IJN20yMuKVcB+cuNBlt0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881070; c=relaxed/simple; bh=SYJkoM5PGYwL725ftsKaTc8bvBhYpRQfbSnmPZHax3c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jxI3jcGKmzVdFsLMq3PMVeA/gbr+o/kiHHk2Jxxnb4AyJFx104wYTWzGdE5WROGC3uUHPoN0rIO1CGfgM7lvQ0AgOyMiQ1xtBdEH/yr6cWfDIoE7vkK493AVPaIucDd326JVQAHHOsPr+4fnS3r2ZT7swb/YCwNxuZ9aJkooC1A= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=awdZS7b1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="awdZS7b1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0BF31C4CECE; Wed, 2 Oct 2024 14:57:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727881070; bh=SYJkoM5PGYwL725ftsKaTc8bvBhYpRQfbSnmPZHax3c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=awdZS7b1nsHiDnErnZfcDNy/1vYhTsJaUk57GzK/w+4XLqRQLgV8tY9KoOHRitF2l EQ3x6edRBguRS8DZqE6jh0vwI6bI391QZZlQ7WocZptxfGhQcnguyErkNt0jLADrSG zqXTN54x9n+WgGyuiWjfN1EWRy/FrOSGAQhOE2mjRLk2kJSzzyqQQLWKpbGaeciv+S jwTbRR/l4DCelLOWk+xRazfYpv1Gxw4O/PLUk9MnTIRGERNZz3I5ZCPdYhNLo+G8/Q tZoYesd75TzH2EDUoHZaqjqPEEE1niDla8mRXUoAV//0iKeg84lmfja/33SHtiEBgN gylgITOO4nJHQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Boqun Feng , Joel Fernandes , Neeraj Upadhyay , "Paul E . McKenney" , Uladzislau Rezki , Zqiang , rcu , kernel test robot Subject: [PATCH 2/3] rcu/nocb: Fix rcuog wake-up from offline softirq Date: Wed, 2 Oct 2024 16:57:37 +0200 Message-ID: <20241002145738.38226-3-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20241002145738.38226-1-frederic@kernel.org> References: <20241002145738.38226-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" After a CPU has set itself offline and before it eventually calls rcutree_report_cpu_dead(), there are still opportunities for callbacks to be enqueued, for example from an IRQ. When that happens on NOCB, the rcuog wake-up is deferred through an IPI to an online CPU in order not to call into the scheduler and risk arming the RT-bandwidth after hrtimers have been migrated out and disabled. But performing a synchronized IPI from an IRQ is buggy as reported in the following scenario: WARNING: CPU: 1 PID: 26 at kernel/smp.c:633 smp_call_function_single Modules linked in: rcutorture torture CPU: 1 UID: 0 PID: 26 Comm: migration/1 Not tainted 6.11.0-rc1-00012-g9139= f93209d1 #1 Stopper: multi_cpu_stop+0x0/0x320 <- __stop_cpus+0xd0/0x120 RIP: 0010:smp_call_function_single swake_up_one_online __call_rcu_nocb_wake __call_rcu_common ? rcu_torture_one_read call_timer_fn __run_timers run_timer_softirq handle_softirqs irq_exit_rcu ? tick_handle_periodic sysvec_apic_timer_interrupt The periodic tick must be shutdown when the CPU is offline, just like is done for oneshot tick. This must be fixed but this is not enough: softirqs can happen on any hardirq tail and reproduce the above scenario. Fix this with introducing a special deferred rcuog wake up mode when the CPU is offline. This deferred wake up doesn't arm any timer and simply wait for rcu_report_cpu_dead() to be called in order to flush any pending rcuog wake up. Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202409231644.4c55582d-lkp@intel.com Fixes: 9139f93209d1 ("rcu/nocb: Fix RT throttling hrtimer armed from offlin= e CPU") Signed-off-by: Frederic Weisbecker Reviewed-by: Joel Fernandes (Google) --- kernel/rcu/tree.h | 1 + kernel/rcu/tree_nocb.h | 14 ++++++++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index a9a811d9d7a3..7ed060edd12b 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -290,6 +290,7 @@ struct rcu_data { #define RCU_NOCB_WAKE_LAZY 2 #define RCU_NOCB_WAKE 3 #define RCU_NOCB_WAKE_FORCE 4 +#define RCU_NOCB_WAKE_OFFLINE 5 =20 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) /* For jiffies_till_first_fqs and */ diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 2fb803f863da..8648233e1717 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -295,6 +295,8 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, in= t waketype, case RCU_NOCB_WAKE_FORCE: if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE) mod_timer(&rdp_gp->nocb_timer, jiffies + 1); + fallthrough; + case RCU_NOCB_WAKE_OFFLINE: if (rdp_gp->nocb_defer_wakeup < waketype) WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); break; @@ -562,8 +564,16 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp,= bool was_alldone, lazy_len =3D READ_ONCE(rdp->lazy_len); if (was_alldone) { rdp->qlen_last_fqs_check =3D len; - // Only lazy CBs in bypass list - if (lazy_len && bypass_len =3D=3D lazy_len) { + if (cpu_is_offline(rdp->cpu)) { + /* + * Offline CPUs can't call swake_up_one_online() from IRQs. Rely + * on the final deferred wake-up rcutree_report_cpu_dead() + */ + rcu_nocb_unlock(rdp); + wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_OFFLINE, + TPS("WakeEmptyIsDeferredOffline")); + } else if (lazy_len && bypass_len =3D=3D lazy_len) { + // Only lazy CBs in bypass list rcu_nocb_unlock(rdp); wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY, TPS("WakeLazy")); --=20 2.46.0 From nobody Thu Nov 28 09:52:49 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 58F4C1D0B89; Wed, 2 Oct 2024 14:57:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881072; cv=none; b=W3tC/W0Kcze5O58FliIzU/yAqqXgwca5OZSPs6gosLC7XgLeEM2E/5BUg+YqvnQWVvgccQWS3mbtD1SwDzYR4tiOOuAORlgNhBo/76J24QAVL9ndQ3TVGB4Jvazs8ixxdRjtAWsH3GgoiV8IBHQihaHROYIPqdQ6fbxhOSLQsRA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727881072; c=relaxed/simple; bh=4jN7m4YdBZpe108+MCUL/gz1eAHliwNklGS/JkzIwho=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PF77DT2VAL9kg1c5zsWX4LXwNBxm0eBdJuLbGpbUQm8vx7B/uUjrVAUJMXRmoUauaLLxWV8lMNPGAneMDSRoWXZyyT/Oq3xmmut0+y8N3A/dT76kvy9zJHmRtdYSuYYAQMMbt/T2VC2hTxzz7Msk+BPZzf+92NOPO28jOwK5yvQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qY58D3Kl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qY58D3Kl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5FC9CC4CECF; Wed, 2 Oct 2024 14:57:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1727881072; bh=4jN7m4YdBZpe108+MCUL/gz1eAHliwNklGS/JkzIwho=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=qY58D3KlK0tRBqsKkUDY1pzUaYqgPGgj7mXMnAMOr2JH2v7LXE3JCU7o6W8gi6Juc JMVrpPX0G0kwPSPLvcbQ2wtUC6YdRjLtqFWRPBJ1m+52f/ICF7E9igm0bE2o0J5BTw jg/7mHZ4EXEhn9StcP3QOLNUn/xlL8pBpY5CdimB34VH6YuqfH1CfQcfb6dZrZu8WY 5FyXZufbzcaHbBQJoQilB04WsZv3XMlw5zwqsU3JnWABQyLFnuLxAMPGVXxoEdDlqB /SeI48Ayq+JvaRqc/lpeMFjTR+3/18N5PwNtsh7lSRnljHgZ0GvX54rlAAg7WdsZL2 SLFjMor11fdIQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Boqun Feng , Joel Fernandes , Neeraj Upadhyay , "Paul E . McKenney" , Uladzislau Rezki , Zqiang , rcu Subject: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind spot Date: Wed, 2 Oct 2024 16:57:38 +0200 Message-ID: <20241002145738.38226-4-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20241002145738.38226-1-frederic@kernel.org> References: <20241002145738.38226-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Callbacks enqueued after rcutree_report_cpu_dead() fall into RCU barrier blind spot. Report any potential misuse. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Reviewed-by: Joel Fernandes (Google) Tested-by: Paul E. McKenney --- kernel/rcu/tree.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a60616e69b66..36070b6bf4a1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3084,8 +3084,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callbac= k_t func, bool lazy_in) head->func =3D func; head->next =3D NULL; kasan_record_aux_stack_noalloc(head); + local_irq_save(flags); rdp =3D this_cpu_ptr(&rcu_data); + RCU_LOCKDEP_WARN(rcu_rdp_cpu_online(rdp), "Callback enqueued on offline C= PU!"); + lazy =3D lazy_in && !rcu_async_should_hurry(); =20 /* Add the callback to our list. */ --=20 2.46.0