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 352CC1C4A24; Mon, 10 Mar 2025 18:02:24 +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=1741629745; cv=none; b=EFZpZx1wg8AyYyFauFUAer5OAGDSPaLVvOLJNK8naZoCuEfKMA1TcAC1DrE5POl3G2ZTfvFx2p/8gX/eqw5rsEYJgN+1vSsCaWnLGW8Wkyc8RYqv9ell7hrMPVChq6cxPsyrk7zobMx8/VezDausGqdMPBycL9iUDGfntXxhTiQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741629745; c=relaxed/simple; bh=g5d9NLG7k54W7ZHSwsCz6RsYLm1Tgnplb1/PGmJUqVw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KAZ1dfpBalHU6kJ7rHWTXWq34iQ1jS0rPm6OoW/dFFPpOq0WnLEVpSxCCCcj1PjhyWPMrtq6DfaTk8b3LF++4zcCW8JgqUNyv7nmjX3VtinKJCrZV5Hjl3oTZyYzyygfyrS7ttHiEiZ5eptthM/rPjQCFZFjIbqJ8UmdPvuamrw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fhqck++Q; 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="fhqck++Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 57A81C4CEE5; Mon, 10 Mar 2025 18:02:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1741629744; bh=g5d9NLG7k54W7ZHSwsCz6RsYLm1Tgnplb1/PGmJUqVw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fhqck++Q4vKiiL/HwM06wNiRHZP7IdRwqXgFiyIAdLCWhL79q54UGtMBybO7pZQT+ kbeolNM1Uh09mCOirDC3XFxOaCXeemyvM7zONtP2g/cPb5XKwFz65mOwiWC4+cU88+ x/Ne5WO5XldG4fbu/sJN4LhsZrDdw+DKhN7dA3Bw= 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 5.15 391/620] clocksource: Use migrate_disable() to avoid calling get_random_u32() in atomic context Date: Mon, 10 Mar 2025 18:03:57 +0100 Message-ID: <20250310170601.029807331@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250310170545.553361750@linuxfoundation.org> References: <20250310170545.553361750@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-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 8d9b11555f7ef..32efc87c41f20 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -342,10 +342,10 @@ 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; @@ -353,6 +353,7 @@ 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; @@ -372,6 +373,7 @@ 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