From mboxrd@z Thu Jan 1 00:00:00 1970 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 B07581C701E; Wed, 19 Feb 2025 09:03:12 +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=1739955792; cv=none; b=EkSsgBl8F9y5zSiD3lGKg0WrhKtfYJ0uaNuAB7YOv7KR4Nlc45LxBJwIhwJKVNMoUtT54kQ6p3ZNFxDU9LYTb/e7n4B0d5bqkEG/9A7ajbwH68hzWAb5OqaA8Z6tg+x36afAjmg8hfGiSHqtXyAtMJR3SGzNJT4H5ZFr9f/ToQg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739955792; c=relaxed/simple; bh=B1+JgsycXNMo8/I4F1QmpquFn6CkJ+6yjz4xY5cD6kI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VsppRAtJfYNnciAC8daUXOjQjv7xfVOlIeoQEZmNW4Z9Tw1x3W8EruOYJE/KiulM1TSbi8+oQ+rqs/yqQv5adUiwqxcUGldYbpDFC/fiAzTL4H/EtZN5BKd61AGnCYT8LOb4zLhfptciFt5Txh+JTO2NDcjiTuEgnS7/ojvza9M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=igM2Nzhz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="igM2Nzhz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 328B7C4CED1; Wed, 19 Feb 2025 09:03:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1739955792; bh=B1+JgsycXNMo8/I4F1QmpquFn6CkJ+6yjz4xY5cD6kI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=igM2NzhzxIqiTgKB9yfKzYK1mK0WVO+SiPhVfDofvYU3ASr6cVcfekZZrdipmSzYH Naiv/Bv/jdMCfhmwS3gXz/ePLkFTD/1xT3LktHLSxWKRrjBC96DNKZaDIQ2GpUpk87 azLae9HGUtuVfUQf9nWUP3OUZ7Q5vPUPILXvWF3M= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sebastian Andrzej Siewior , Waiman Long , Thomas Gleixner , "Paul E. McKenney" , Sasha Levin Subject: [PATCH 6.6 098/152] clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context Date: Wed, 19 Feb 2025 09:28:31 +0100 Message-ID: <20250219082553.935115306@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250219082550.014812078@linuxfoundation.org> References: <20250219082550.014812078@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Waiman Long [ Upstream commit 6bb05a33337b2c842373857b63de5c9bf1ae2a09 ] The following bug report happened with a PREEMPT_RT kernel: BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 2012, name: kwatchdog preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 get_random_u32+0x4f/0x110 clocksource_verify_choose_cpus+0xab/0x1a0 clocksource_verify_percpu.part.0+0x6b/0x330 clocksource_watchdog_kthread+0x193/0x1a0 It is due to the fact that clocksource_verify_choose_cpus() is invoked with preemption disabled. This function invokes get_random_u32() to obtain random numbers for choosing CPUs. The batched_entropy_32 local lock and/or the base_crng.lock spinlock in driver/char/random.c will be acquired during the call. In PREEMPT_RT kernel, they are both sleeping locks and so cannot be acquired in atomic context. Fix this problem by using migrate_disable() to allow smp_processor_id() to be reliably used without introducing atomic context. preempt_disable() is then called after clocksource_verify_choose_cpus() but before the clocksource measurement is being run to avoid introducing unexpected latency. Fixes: 7560c02bdffb ("clocksource: Check per-CPU clock synchronization when marked unstable") Suggested-by: Sebastian Andrzej Siewior Signed-off-by: Waiman Long Signed-off-by: Thomas Gleixner Reviewed-by: Paul E. McKenney Reviewed-by: Sebastian Andrzej Siewior Link: https://lore.kernel.org/all/20250131173323.891943-2-longman@redhat.com Signed-off-by: Sasha Levin --- kernel/time/clocksource.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 6b5b7c9c14732..3130f24daf597 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -351,10 +351,10 @@ void clocksource_verify_percpu(struct clocksource *cs) cpumask_clear(&cpus_ahead); cpumask_clear(&cpus_behind); cpus_read_lock(); - preempt_disable(); + migrate_disable(); clocksource_verify_choose_cpus(); if (cpumask_empty(&cpus_chosen)) { - preempt_enable(); + migrate_enable(); cpus_read_unlock(); pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); return; @@ -362,6 +362,7 @@ void clocksource_verify_percpu(struct clocksource *cs) testcpu = smp_processor_id(); pr_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); + preempt_disable(); for_each_cpu(cpu, &cpus_chosen) { if (cpu == testcpu) continue; @@ -381,6 +382,7 @@ void clocksource_verify_percpu(struct clocksource *cs) cs_nsec_min = cs_nsec; } preempt_enable(); + migrate_enable(); cpus_read_unlock(); if (!cpumask_empty(&cpus_ahead)) pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", -- 2.39.5