Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934496AbbHDOyf (ORCPT ); Tue, 4 Aug 2015 10:54:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:59202 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964945AbbHDOmN (ORCPT ); Tue, 4 Aug 2015 10:42:13 -0400 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Steven Rostedt (Red Hat)" , Jiri Slaby Subject: [PATCH 3.12 090/123] tracing: Have branch tracer use recursive field of task struct Date: Tue, 4 Aug 2015 16:40:34 +0200 Message-Id: X-Mailer: git-send-email 2.5.0 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3530 Lines: 104 From: "Steven Rostedt (Red Hat)" 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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: Jiri Slaby --- kernel/trace/trace.h | 1 + kernel/trace/trace_branch.c | 17 ++++++++++------- 2 files changed, 11 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 7e8be3e50f83..be4f503787cb 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -420,6 +420,7 @@ 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 diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c index d594da0dc03c..cb89197adf5c 100644 --- a/kernel/trace/trace_branch.c +++ b/kernel/trace/trace_branch.c @@ -37,9 +37,12 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect) 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_branch_data *f, int val, int expect) 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_branch_data *f, int val, int expect) __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 -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/