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 4A13D1C82F4; Wed, 19 Feb 2025 08:40:18 +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=1739954418; cv=none; b=ne+yPhlA0iNboVOTgU/BSLY/m12tIj5qGQDqvU2QGhw4F1bFj6xLAZvUSoVZp7M3R+gQ3VpzhU5cKE9YNM2QXYdAtHNNFBTBC0xLpI3GfppfWA3168ZvyJBgEllINw2M9rZThljhrYFKXVXVVC2DzhA29B9C832f2xBdZx/kuew= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739954418; c=relaxed/simple; bh=p534Dg/GgL3gteCIM8xwVRPKYBfi/k5Bvfv86xcO9GI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=aPENXa5cSKq9MfOhBOR9SqhPldx1hYvncG32bgZycMRY/1PfhAzxKyEbSjzB4GSPjvstNvzJOiI1zu8hHBCLX9wctRROZGpVKRKNphQHqr1iJ40hN9eyaAW5Hiu4fkeJWx7oKiuOueXztxRAcUuxPhBxSIu2UyytarFcRu4JrMg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Ix6imb6U; 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="Ix6imb6U" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C017AC4CEE8; Wed, 19 Feb 2025 08:40:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1739954418; bh=p534Dg/GgL3gteCIM8xwVRPKYBfi/k5Bvfv86xcO9GI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ix6imb6UsqNuB4fABLZ9JH0lqeQjH1R5AZY85PTU8NZWD1c19b05FBue0fFtX6MO9 my8pXhETq00r6jUt9DaB+0Gj+KaiADFw96JknbYwE/y2L/lTC9Ax/PvN5bGLnhHpPd N969PSM8Q9ZQTyFyEvMkfx0f4pVo+ktI3Pq8z1mA= 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 6.13 198/274] clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context Date: Wed, 19 Feb 2025 09:27:32 +0100 Message-ID: <20250219082617.331756652@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250219082609.533585153@linuxfoundation.org> References: <20250219082609.533585153@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 6.13-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 77d9566d3aa68..2a7802ec480cc 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -373,10 +373,10 @@ 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; @@ -384,6 +384,7 @@ 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; @@ -403,6 +404,7 @@ 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