From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754404Ab1DUBny (ORCPT ); Wed, 20 Apr 2011 21:43:54 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:63641 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752533Ab1DUBnE (ORCPT ); Wed, 20 Apr 2011 21:43:04 -0400 X-Authority-Analysis: v=1.1 cv=ZtuXOl23UuD1yoJUTgnZ6i6Z5VPlPhPMWCeUNtN8OGA= c=1 sm=0 a=vhdKIqpQuCYA:10 a=iKYZGZOP-K4A:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=20KFwNOVAAAA:8 a=meVymXHHAAAA:8 a=JneOFEaHyrGEK7axOc0A:9 a=ZOvx8THDl3A8O_X6SWIA:7 a=jEp0ucaQiEUA:10 a=jeBq3FmKZ4MA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Message-Id: <20110421014259.380621789@goodmis.org> User-Agent: quilt/0.48-1 Date: Wed, 20 Apr 2011 21:41:55 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , "H. Peter Anvin" , Frederic Weisbecker , Peter Zijlstra Subject: [PATCH 2/7] lockdep: Print a nice description of normal deadlocks References: <20110421014153.126662477@goodmis.org> Content-Disposition: inline; filename=0002-lockdep-Print-a-nice-description-of-normal-deadlocks.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Steven Rostedt The lockdep output can be pretty cryptic, having a nice output can save a lot of head scratching. When a normal deadlock scenario is detected by lockdep (lock A -> lock B and there exists a place where lock B -> lock A) we get the following output: other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(lockB); lock(lockA); lock(lockB); lock(lockA); *** DEADLOCK *** On cases where there's a deeper chair, it shows the partial chain that can cause the issue: Chain exists of: lockC --> lockA --> lockB Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(lockB); lock(lockA); lock(lockB); lock(lockC); *** DEADLOCK *** Acked-by: Peter Zijlstra Signed-off-by: Steven Rostedt --- kernel/lockdep.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 55 insertions(+), 0 deletions(-) diff --git a/kernel/lockdep.c b/kernel/lockdep.c index bb77c030..1039008 100644 --- a/kernel/lockdep.c +++ b/kernel/lockdep.c @@ -1065,6 +1065,56 @@ print_circular_bug_entry(struct lock_list *target, int depth) return 0; } +static void +print_circular_lock_scenario(struct held_lock *src, + struct held_lock *tgt, + struct lock_list *prt) +{ + struct lock_class *source = hlock_class(src); + struct lock_class *target = hlock_class(tgt); + struct lock_class *parent = prt->class; + + /* + * A direct locking problem where unsafe_class lock is taken + * directly by safe_class lock, then all we need to show + * is the deadlock scenario, as it is obvious that the + * unsafe lock is taken under the safe lock. + * + * But if there is a chain instead, where the safe lock takes + * an intermediate lock (middle_class) where this lock is + * not the same as the safe lock, then the lock chain is + * used to describe the problem. Otherwise we would need + * to show a different CPU case for each link in the chain + * from the safe_class lock to the unsafe_class lock. + */ + if (parent != source) { + printk("Chain exists of:\n "); + __print_lock_name(source); + printk(" --> "); + __print_lock_name(parent); + printk(" --> "); + __print_lock_name(target); + printk("\n\n"); + } + + printk(" Possible unsafe locking scenario:\n\n"); + printk(" CPU0 CPU1\n"); + printk(" ---- ----\n"); + printk(" lock("); + __print_lock_name(target); + printk(");\n"); + printk(" lock("); + __print_lock_name(parent); + printk(");\n"); + printk(" lock("); + __print_lock_name(target); + printk(");\n"); + printk(" lock("); + __print_lock_name(source); + printk(");\n"); + printk("\n *** DEADLOCK ***\n\n"); +} + /* * When a circular dependency is detected, print the * header first: @@ -1108,6 +1158,7 @@ static noinline int print_circular_bug(struct lock_list *this, { struct task_struct *curr = current; struct lock_list *parent; + struct lock_list *first_parent; int depth; if (!debug_locks_off_graph_unlock() || debug_locks_silent) @@ -1121,6 +1172,7 @@ static noinline int print_circular_bug(struct lock_list *this, print_circular_bug_header(target, depth, check_src, check_tgt); parent = get_lock_parent(target); + first_parent = parent; while (parent) { print_circular_bug_entry(parent, --depth); @@ -1128,6 +1180,9 @@ static noinline int print_circular_bug(struct lock_list *this, } printk("\nother info that might help us debug this:\n\n"); + print_circular_lock_scenario(check_src, check_tgt, + first_parent); + lockdep_print_held_locks(curr); printk("\nstack backtrace:\n"); -- 1.7.2.3