From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753515AbdHODA5 (ORCPT ); Mon, 14 Aug 2017 23:00:57 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:37876 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753208AbdHODAy (ORCPT ); Mon, 14 Aug 2017 23:00:54 -0400 From: Sergey Senozhatsky To: Petr Mladek , Steven Rostedt Cc: Jan Kara , Andrew Morton , Peter Zijlstra , "Rafael J . Wysocki" , Eric Biederman , Greg Kroah-Hartman , Jiri Slaby , Pavel Machek , Andreas Mohr , Tetsuo Handa , linux-kernel@vger.kernel.org, Sergey Senozhatsky , Sergey Senozhatsky Subject: [RFC][PATCHv5 12/13] printk: do not cond_resched() when we can offload Date: Tue, 15 Aug 2017 11:56:24 +0900 Message-Id: <20170815025625.1977-13-sergey.senozhatsky@gmail.com> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170815025625.1977-1-sergey.senozhatsky@gmail.com> References: <20170815025625.1977-1-sergey.senozhatsky@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org console_unlock() may sleep with console_sem locked, which is a bit counter intuitive: we neither print pending logbuf messages to the serial console, nor let anyone else to do it for us. With printing offloading enabled, however, we can disable preemption, because we know for sure how long we can stay in console_unlock() and that eventually we will offload to another task. Signed-off-by: Sergey Senozhatsky --- kernel/printk/printk.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 0ffbaa33280f..ba82152ce5d9 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2432,6 +2432,14 @@ void console_unlock(void) * and cleared after the the "again" goto label. */ do_cond_resched = console_may_schedule; + /* + * Forbid scheduling under the console_sem lock when offloading + * is enabled. Scheduling will just slow down the print out in + * this case. + */ + if (printk_offloading_enabled() && is_printk_offloading_safe()) + do_cond_resched = 0; + again: console_may_schedule = 0; @@ -2447,6 +2455,7 @@ void console_unlock(void) return; } + preempt_disable(); for (;;) { struct printk_log *msg; size_t ext_len = 0; @@ -2507,8 +2516,11 @@ void console_unlock(void) start_critical_timings(); printk_safe_exit_irqrestore(flags); - if (do_cond_resched) + if (do_cond_resched) { + preempt_enable(); cond_resched(); + preempt_disable(); + } } console_locked = 0; @@ -2518,6 +2530,7 @@ void console_unlock(void) raw_spin_unlock(&logbuf_lock); + preempt_enable(); up_console_sem(); /* -- 2.14.1