From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:35895 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751013AbbGaALg (ORCPT ); Thu, 30 Jul 2015 20:11:36 -0400 Subject: Patch "tracing: Have branch tracer use recursive field of task struct" has been added to the 3.14-stable tree To: rostedt@goodmis.org, fengguang.wu@intel.com, gregkh@linuxfoundation.org Cc: , From: Date: Thu, 30 Jul 2015 17:11:35 -0700 Message-ID: <14383014959541@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled tracing: Have branch tracer use recursive field of task struct to the 3.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tracing-have-branch-tracer-use-recursive-field-of-task-struct.patch and it can be found in the queue-3.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 6224beb12e190ff11f3c7d4bf50cb2922878f600 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Tue, 7 Jul 2015 15:05:03 -0400 Subject: tracing: Have branch tracer use recursive field of task struct From: "Steven Rostedt (Red Hat)" commit 6224beb12e190ff11f3c7d4bf50cb2922878f600 upstream. Fengguang Wu's tests triggered a bug in the branch tracer's start up test when CONFIG_DEBUG_PREEMPT set. This was because that config adds some debug logic in the per cpu field, which calls back into the branch tracer. The branch tracer has its own recursive checks, but uses a per cpu variable to implement it. If retrieving the per cpu variable calls back into the branch tracer, you can see how things will break. Instead of using a per cpu variable, use the trace_recursion field of the current task struct. Simply set a bit when entering the branch tracing and clear it when leaving. If the bit is set on entry, just don't do the tracing. There's also the case with lockdep, as the local_irq_save() called before the recursion can also trigger code that can call back into the function. Changing that to a raw_local_irq_save() will protect that as well. This prevents the recursion and the inevitable crash that follows. Link: http://lkml.kernel.org/r/20150630141803.GA28071@wfg-t540p.sh.intel.com Reported-by: Fengguang Wu Tested-by: Fengguang Wu Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.h | 1 + kernel/trace/trace_branch.c | 17 ++++++++++------- 2 files changed, 11 insertions(+), 7 deletions(-) --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -422,6 +422,7 @@ enum { TRACE_CONTROL_BIT, + TRACE_BRANCH_BIT, /* * Abuse of the trace_recursion. * As we need a way to maintain state if we are tracing the function --- a/kernel/trace/trace_branch.c +++ b/kernel/trace/trace_branch.c @@ -37,9 +37,12 @@ probe_likely_condition(struct ftrace_bra struct trace_branch *entry; struct ring_buffer *buffer; unsigned long flags; - int cpu, pc; + int pc; const char *p; + if (current->trace_recursion & TRACE_BRANCH_BIT) + return; + /* * I would love to save just the ftrace_likely_data pointer, but * this code can also be used by modules. Ugly things can happen @@ -50,10 +53,10 @@ probe_likely_condition(struct ftrace_bra if (unlikely(!tr)) return; - local_irq_save(flags); - cpu = raw_smp_processor_id(); - data = per_cpu_ptr(tr->trace_buffer.data, cpu); - if (atomic_inc_return(&data->disabled) != 1) + raw_local_irq_save(flags); + current->trace_recursion |= TRACE_BRANCH_BIT; + data = this_cpu_ptr(tr->trace_buffer.data); + if (atomic_read(&data->disabled)) goto out; pc = preempt_count(); @@ -82,8 +85,8 @@ probe_likely_condition(struct ftrace_bra __buffer_unlock_commit(buffer, event); out: - atomic_dec(&data->disabled); - local_irq_restore(flags); + current->trace_recursion &= ~TRACE_BRANCH_BIT; + raw_local_irq_restore(flags); } static inline Patches currently in stable-queue which might be from rostedt@goodmis.org are queue-3.14/tracing-have-branch-tracer-use-recursive-field-of-task-struct.patch queue-3.14/tracing-filter-do-not-allow-infix-to-exceed-end-of-string.patch queue-3.14/tracing-filter-do-not-warn-on-operand-count-going-below-zero.patch