From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752563Ab0CSNyz (ORCPT ); Fri, 19 Mar 2010 09:54:55 -0400 Received: from mail.openrapids.net ([64.15.138.104]:38747 "EHLO blackscsi.openrapids.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752203Ab0CSNyy (ORCPT ); Fri, 19 Mar 2010 09:54:54 -0400 Date: Fri, 19 Mar 2010 09:54:51 -0400 From: Mathieu Desnoyers To: "Paul E. McKenney" Cc: Lai Jiangshan , mingo@elte.hu, akpm@linux-foundation.org, dipankar@in.ibm.com, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, Alexey Dobriyan , Peter Zijlstra , linux-kernel@vger.kernel.org, Christoph Lameter , Pekka Enberg Subject: Re: [PATCH] tree/tiny rcu: Add debug RCU head option (v2) Message-ID: <20100319135451.GA18079@Krystal> References: <20100319013024.GA28456@Krystal> <4BA2FA01.30102@cn.fujitsu.com> <20100319050532.GE2894@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100319050532.GE2894@linux.vnet.ibm.com> X-Editor: vi X-Info: http://www.efficios.com X-Operating-System: Linux/2.6.26-2-686 (i686) X-Uptime: 09:52:05 up 55 days, 16:29, 8 users, load average: 1.20, 1.10, 1.09 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > On Fri, Mar 19, 2010 at 12:13:53PM +0800, Lai Jiangshan wrote: > > CC: Christoph Lameter > > CC: Pekka Enberg > > > > I have written a patch like this before. > > > > but SLUB opposed me, so I did not post it. > > > > @ slub.c > > static void free_slab(struct kmem_cache *s, struct page *page) > > { > > if (unlikely(s->flags & SLAB_DESTROY_BY_RCU)) { > > /* > > * RCU free overloads the RCU head over the LRU > > */ > > struct rcu_head *head = (void *)&page->lru; > > > > call_rcu(head, rcu_free_slab); > > } else > > __free_slab(s, page); > > } > > > > I think it is not your patch's fault, but the above code has > > already existed. > > > > In your patch, struct rcu_head::debug will share the same memory of > > the other field of struct page, (especially share the struct page::flags > > which I encountered) > > > > I tested it very long time before, so I can't give you dmesg. > > Ouch!!! > > If this only causes a problem for SLUB, maybe a workaround is to make > the config variable depend on !SLUB. But this would seem to increase > the urgency of using the debug objects Hrm.. looking into the port to debugobjects, there are a few things that are not precisely well set at the moment for it: - We need to have two distinct active states, with a check that we move between the two. This does not seem to be currently supported by debugobjects. - RCU heads are never explicitely freed. So yeah, that means we will have to modify a lot of callers. Thanks, Mathieu > > Thanx, Paul > > > Lai > > > > Mathieu Desnoyers wrote: > > > Poisoning the rcu_head callback list. > > > > > > Helps finding racy users of call_rcu(), which results in hangs because list > > > entries are overwritten and/or skipped. > > > > > > A lot of non-initialized rcu list heads will be found with this option enabled. > > > It is important to do not just blindly initialize them before each call_rcu, but > > > rather to perform the initialization at the proper location, after the memory > > > has been allocated, so we can effectively detect incorrect call_rcu users. > > > > > > This patch version does not use "debug objects", although it probably should. > > > Some day I might find time to look into this transition, but the patch is usable > > > as is. > > > > > > The weird #ifdef in the networking code comes from an agreement with Eric > > > Dumazet about how to disable the build check for the networking code. For those > > > who wonder about the existence of this build-time check: it generates a build > > > error when the size of struct dst_entry grows (because it is very performance > > > sensitive). So the agreement here has been to disable the check when the > > > DEBUG_RCU_HEAD config option is active. > > > > > > Signed-off-by: Mathieu Desnoyers > > > CC: "Paul E. McKenney" > > > CC: mingo@elte.hu > > > CC: akpm@linux-foundation.org > > > CC: mingo@elte.hu > > > CC: laijs@cn.fujitsu.com > > > CC: dipankar@in.ibm.com > > > CC: josh@joshtriplett.org > > > CC: dvhltc@us.ibm.com > > > CC: niv@us.ibm.com > > > CC: tglx@linutronix.de > > > CC: peterz@infradead.org > > > CC: rostedt@goodmis.org > > > CC: Valdis.Kletnieks@vt.edu > > > CC: dhowells@redhat.com > > > CC: eric.dumazet@gmail.com > > > CC: Alexey Dobriyan > > > CC: Peter Zijlstra > > > --- > > > include/linux/rcupdate.h | 13 ++++++++++++- > > > include/net/dst.h | 2 ++ > > > kernel/rcutiny.c | 9 +++++++++ > > > kernel/rcutree.c | 10 ++++++++++ > > > lib/Kconfig.debug | 9 +++++++++ > > > 5 files changed, 42 insertions(+), 1 deletion(-) > > > > > > Index: linux-2.6-lttng/include/linux/rcupdate.h > > > =================================================================== > > > --- linux-2.6-lttng.orig/include/linux/rcupdate.h 2010-03-18 20:27:25.000000000 -0400 > > > +++ linux-2.6-lttng/include/linux/rcupdate.h 2010-03-18 20:30:54.000000000 -0400 > > > @@ -49,6 +49,9 @@ > > > struct rcu_head { > > > struct rcu_head *next; > > > void (*func)(struct rcu_head *head); > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > + struct rcu_head *debug; > > > +#endif > > > }; > > > > > > /* Exported common interfaces */ > > > @@ -71,11 +74,19 @@ extern void rcu_init(void); > > > #error "Unknown RCU implementation specified to kernel configuration" > > > #endif > > > > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > +#define RCU_HEAD_INIT { .next = NULL, .func = NULL, .debug = NULL } > > > +#define INIT_RCU_HEAD(ptr) do { \ > > > + (ptr)->next = NULL; (ptr)->func = NULL; (ptr)->debug = NULL; \ > > > +} while (0) > > > +#else > > > #define RCU_HEAD_INIT { .next = NULL, .func = NULL } > > > -#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT > > > #define INIT_RCU_HEAD(ptr) do { \ > > > (ptr)->next = NULL; (ptr)->func = NULL; \ > > > } while (0) > > > +#endif > > > + > > > +#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT > > > > > > #ifdef CONFIG_DEBUG_LOCK_ALLOC > > > extern struct lockdep_map rcu_lock_map; > > > Index: linux-2.6-lttng/kernel/rcutree.c > > > =================================================================== > > > --- linux-2.6-lttng.orig/kernel/rcutree.c 2010-03-18 20:27:25.000000000 -0400 > > > +++ linux-2.6-lttng/kernel/rcutree.c 2010-03-18 20:31:16.000000000 -0400 > > > @@ -39,6 +39,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > #include > > > #include > > > #include > > > @@ -1060,6 +1061,10 @@ static void rcu_do_batch(struct rcu_stat > > > next = list->next; > > > prefetch(next); > > > trace_rcu_tree_callback(list); > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > + WARN_ON_ONCE(list->debug != LIST_POISON1); > > > + list->debug = NULL; > > > +#endif > > > list->func(list); > > > list = next; > > > if (++count >= rdp->blimit) > > > @@ -1350,6 +1355,11 @@ __call_rcu(struct rcu_head *head, void ( > > > unsigned long flags; > > > struct rcu_data *rdp; > > > > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > + WARN_ON_ONCE(head->debug); > > > + head->debug = LIST_POISON1; > > > +#endif > > > + > > > head->func = func; > > > head->next = NULL; > > > > > > Index: linux-2.6-lttng/lib/Kconfig.debug > > > =================================================================== > > > --- linux-2.6-lttng.orig/lib/Kconfig.debug 2010-03-18 20:27:25.000000000 -0400 > > > +++ linux-2.6-lttng/lib/Kconfig.debug 2010-03-18 20:27:38.000000000 -0400 > > > @@ -661,6 +661,15 @@ config DEBUG_LIST > > > > > > If unsure, say N. > > > > > > +config DEBUG_RCU_HEAD > > > + bool "Debug RCU callbacks" > > > + depends on DEBUG_KERNEL > > > + depends on TREE_RCU > > > + help > > > + Enable this to turn on debugging of RCU list heads (call_rcu() usage). > > > + Seems to find problems more quickly with stress-tests in single-cpu > > > + mode. > > > + > > > config DEBUG_SG > > > bool "Debug SG table operations" > > > depends on DEBUG_KERNEL > > > Index: linux-2.6-lttng/include/net/dst.h > > > =================================================================== > > > --- linux-2.6-lttng.orig/include/net/dst.h 2010-03-18 20:27:25.000000000 -0400 > > > +++ linux-2.6-lttng/include/net/dst.h 2010-03-18 20:35:02.000000000 -0400 > > > @@ -159,7 +159,9 @@ static inline void dst_hold(struct dst_e > > > * If your kernel compilation stops here, please check > > > * __pad_to_align_refcnt declaration in struct dst_entry > > > */ > > > +#ifndef CONFIG_DEBUG_RCU_HEAD > > > BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63); > > > +#endif > > > atomic_inc(&dst->__refcnt); > > > } > > > > > > Index: linux-2.6-lttng/kernel/rcutiny.c > > > =================================================================== > > > --- linux-2.6-lttng.orig/kernel/rcutiny.c 2010-03-18 20:35:14.000000000 -0400 > > > +++ linux-2.6-lttng/kernel/rcutiny.c 2010-03-18 20:39:12.000000000 -0400 > > > @@ -35,6 +35,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > /* Global control variables for rcupdate callback mechanism. */ > > > struct rcu_ctrlblk { > > > @@ -163,6 +164,10 @@ static void __rcu_process_callbacks(stru > > > while (list) { > > > next = list->next; > > > prefetch(next); > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > + WARN_ON_ONCE(list->debug != LIST_POISON1); > > > + list->debug = NULL; > > > +#endif > > > list->func(list); > > > list = next; > > > } > > > @@ -210,6 +215,10 @@ static void __call_rcu(struct rcu_head * > > > { > > > unsigned long flags; > > > > > > +#ifdef CONFIG_DEBUG_RCU_HEAD > > > + WARN_ON_ONCE(head->debug); > > > + head->debug = LIST_POISON1; > > > +#endif > > > head->func = func; > > > head->next = NULL; > > > > > > > > -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com