From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751250Ab0CSFFi (ORCPT ); Fri, 19 Mar 2010 01:05:38 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:58945 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751094Ab0CSFFh (ORCPT ); Fri, 19 Mar 2010 01:05:37 -0400 Date: Thu, 18 Mar 2010 22:05:32 -0700 From: "Paul E. McKenney" To: Lai Jiangshan Cc: Mathieu Desnoyers , 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: <20100319050532.GE2894@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100319013024.GA28456@Krystal> <4BA2FA01.30102@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BA2FA01.30102@cn.fujitsu.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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; > > > > >