From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753026AbcESFhz (ORCPT ); Thu, 19 May 2016 01:37:55 -0400 Received: from g2t2354.austin.hpe.com ([15.233.44.27]:56671 "EHLO g2t2354.austin.hpe.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751301AbcESFhy (ORCPT ); Thu, 19 May 2016 01:37:54 -0400 X-Greylist: delayed 160746 seconds by postgrey-1.27 at vger.kernel.org; Thu, 19 May 2016 01:37:54 EDT From: Soumya PN To: rostedt@goodmis.org, mingo@redhat.com Cc: linux-kernel@vger.kernel.org, chandru.muthu@hpe.com, Soumya PN Subject: [PATCH] ftrace: As disabling interrupts is costly and write_lock variant of tasklist_lock is not held from interrupt context it is not necessary to disable interrupts. Date: Thu, 19 May 2016 18:10:13 +0530 Message-Id: <1463661613-43970-1-git-send-email-soumya.p.n@hpe.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In ftrace.c inside the function alloc_retstack_tasklist()(which will be invoked when function_graph tracing is on) the tasklist_lock is being held as reader while iterating through list of threads. Here the lock being held as reader with irqs disabled. The tasklist_lock is never write_locked in interrupt context so it is safe to not disable interrupts for the duration of read_lock in this block which, can be significant, given the block of code iterates through all threads. Hence changing the code to call read_lock() and read_unlock() instead of read_lock_irqsave() and read_unlock_irqrestore(). Seen the same change is made in "kernel/tracepoint.c" and "kernel/sched/core.c"files with commit ids 'commit 8063e41d2ffc ("tracing: Change syscall_*regfunc() to check PF_KTHREAD and use for_each_process_thread()")' 'commit 3472eaa1f12e ("sched: normalize_rt_tasks(): Don't use _irqsave for tasklist_lock, use task_rq_lock()")' Done basic testing by enabling function graph tracing in x86_64. Signed-off-by: Soumya PN --- kernel/trace/ftrace.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index b1870fb..45bc72f 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5713,7 +5713,6 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list) { int i; int ret = 0; - unsigned long flags; int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE; struct task_struct *g, *t; @@ -5728,8 +5727,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list) goto free; } } - - read_lock_irqsave(&tasklist_lock, flags); + read_lock(&tasklist_lock); do_each_thread(g, t) { if (start == end) { ret = -EAGAIN; @@ -5747,7 +5745,7 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list) } while_each_thread(g, t); unlock: - read_unlock_irqrestore(&tasklist_lock, flags); + read_unlock(&tasklist_lock); free: for (i = start; i < end; i++) kfree(ret_stack_list[i]); -- 1.8.3.1