From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752858Ab3E1SmM (ORCPT ); Tue, 28 May 2013 14:42:12 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:27399 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751065Ab3E1SmL (ORCPT ); Tue, 28 May 2013 14:42:11 -0400 X-Authority-Analysis: v=2.0 cv=MNbiabll c=1 sm=0 a=rXTBtCOcEpjy1lPqhTCpEQ==:17 a=mNMOxpOpBa8A:10 a=Ciwy3NGCPMMA:10 a=U_UBT7BNE-4A:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=meVymXHHAAAA:8 a=FFjlQw3OIPcA:10 a=2E_tCxuvyUkL-5MFE2wA:9 a=jeBq3FmKZ4MA:10 a=rXTBtCOcEpjy1lPqhTCpEQ==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 74.67.115.198 Message-Id: <20130528184209.304356745@goodmis.org> User-Agent: quilt/0.60-1 Date: Tue, 28 May 2013 14:38:42 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: "Paul E. McKenney" , Ingo Molnar , Andrew Morton Subject: [PATCH 1/2] rcu: Add _notrace variation of rcu_dereference_raw() and hlist_for_each_entry_rcu() References: <20130528183841.535484906@goodmis.org> Content-Disposition: inline; filename=add_rcu_dereference_raw_notrace.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As rcu_dereference_raw() under RCU debug config options can add quite a bit of checks, and that tracing uses rcu_dereference_raw(), these checks happen with the function tracer. The function tracer also happens to trace these debug checks too. This added overhead can livelock the system. Add a new interface to RCU for both rcu_dereference_raw_notrace() as well as hlist_for_each_entry_rcu_notrace() as the hlist iterator uses the rcu_dereference_raw() as well, and is used a bit with the function tracer. Signed-off-by: Steven Rostedt Index: linux-trace.git/include/linux/rculist.h =================================================================== --- linux-trace.git.orig/include/linux/rculist.h +++ linux-trace.git/include/linux/rculist.h @@ -461,6 +461,26 @@ static inline void hlist_add_after_rcu(s &(pos)->member)), typeof(*(pos)), member)) /** + * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing) + * @pos: the type * to use as a loop cursor. + * @head: the head for your list. + * @member: the name of the hlist_node within the struct. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as hlist_add_head_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + * + * This is the same as hlist_for_each_entry_rcu() except that it does + * not do any RCU debugging or tracing. + */ +#define hlist_for_each_entry_rcu_notrace(pos, head, member) \ + for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\ + typeof(*(pos)), member); \ + pos; \ + pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\ + &(pos)->member)), typeof(*(pos)), member)) + +/** * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type * @pos: the type * to use as a loop cursor. * @head: the head for your list. Index: linux-trace.git/include/linux/rcupdate.h =================================================================== --- linux-trace.git.orig/include/linux/rcupdate.h +++ linux-trace.git/include/linux/rcupdate.h @@ -640,6 +640,15 @@ static inline void rcu_preempt_sleep_che #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ +/* + * The tracing infrastructure traces RCU (we want that), but unfortunately + * some of the RCU checks causes tracing to lock up the system. + * + * The tracing version of rcu_dereference_raw() must not call + * rcu_read_lock_held(). + */ +#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu) + /** * rcu_access_index() - fetch RCU index with no dereferencing * @p: The index to read