From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751904AbeAZWXQ (ORCPT ); Fri, 26 Jan 2018 17:23:16 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:45284 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751404AbeAZWXP (ORCPT ); Fri, 26 Jan 2018 17:23:15 -0500 Date: Fri, 26 Jan 2018 14:22:59 -0800 From: "Paul E. McKenney" To: Lihao Liang Cc: "Guohanjun (Hanjun Guo)" , heng.z@huawei.com, hb.chen@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 07/16] prcu: Implement call_prcu() API Reply-To: paulmck@linux.vnet.ibm.com References: <1516694381-20333-1-git-send-email-lianglihao@huawei.com> <1516694381-20333-8-git-send-email-lianglihao@huawei.com> <20180125062031.GW3741@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18012622-0040-0000-0000-000003E9BDB0 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008433; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000248; SDB=6.00980813; UDB=6.00497241; IPR=6.00760114; BA=6.00005797; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00019234; XFM=3.00000015; UTC=2018-01-26 22:23:01 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18012622-0041-0000-0000-000007DF2677 Message-Id: <20180126222259.GJ3741@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-01-26_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1801260292 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 26, 2018 at 08:44:50AM +0000, Lihao Liang wrote: > On Thu, Jan 25, 2018 at 6:20 AM, Paul E. McKenney > wrote: > > On Tue, Jan 23, 2018 at 03:59:32PM +0800, lianglihao@huawei.com wrote: > >> From: Lihao Liang > >> > >> This is PRCU's counterpart of RCU's call_rcu() API. > >> > >> Reviewed-by: Heng Zhang > >> Signed-off-by: Lihao Liang > >> --- > >> include/linux/prcu.h | 25 ++++++++++++++++++++ > >> init/main.c | 2 ++ > >> kernel/rcu/prcu.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++--- > >> 3 files changed, 91 insertions(+), 3 deletions(-) > >> > >> diff --git a/include/linux/prcu.h b/include/linux/prcu.h > >> index 653b4633..e5e09c9b 100644 > >> --- a/include/linux/prcu.h > >> +++ b/include/linux/prcu.h > >> @@ -2,15 +2,36 @@ > >> #define __LINUX_PRCU_H > >> > >> #include > >> +#include > >> #include > >> #include > >> > >> #define CONFIG_PRCU > >> > >> +struct prcu_version_head { > >> + unsigned long long version; > >> + struct prcu_version_head *next; > >> +}; > >> + > >> +/* Simple unsegmented callback list for PRCU. */ > >> +struct prcu_cblist { > >> + struct rcu_head *head; > >> + struct rcu_head **tail; > >> + struct prcu_version_head *version_head; > >> + struct prcu_version_head **version_tail; > >> + long len; > >> +}; > >> + > >> +#define PRCU_CBLIST_INITIALIZER(n) { \ > >> + .head = NULL, .tail = &n.head, \ > >> + .version_head = NULL, .version_tail = &n.version_head, \ > >> +} > >> + > >> struct prcu_local_struct { > >> unsigned int locked; > >> unsigned int online; > >> unsigned long long version; > >> + struct prcu_cblist cblist; > >> }; > >> > >> struct prcu_struct { > >> @@ -24,6 +45,8 @@ struct prcu_struct { > >> void prcu_read_lock(void); > >> void prcu_read_unlock(void); > >> void synchronize_prcu(void); > >> +void call_prcu(struct rcu_head *head, rcu_callback_t func); > >> +void prcu_init(void); > >> void prcu_note_context_switch(void); > >> > >> #else /* #ifdef CONFIG_PRCU */ > >> @@ -31,6 +54,8 @@ void prcu_note_context_switch(void); > >> #define prcu_read_lock() do {} while (0) > >> #define prcu_read_unlock() do {} while (0) > >> #define synchronize_prcu() do {} while (0) > >> +#define call_prcu() do {} while (0) > >> +#define prcu_init() do {} while (0) > >> #define prcu_note_context_switch() do {} while (0) > >> > >> #endif /* #ifdef CONFIG_PRCU */ > >> diff --git a/init/main.c b/init/main.c > >> index f8665104..4925964e 100644 > >> --- a/init/main.c > >> +++ b/init/main.c > >> @@ -38,6 +38,7 @@ > >> #include > >> #include > >> #include > >> +#include > >> #include > >> #include > >> #include > >> @@ -574,6 +575,7 @@ asmlinkage __visible void __init start_kernel(void) > >> workqueue_init_early(); > >> > >> rcu_init(); > >> + prcu_init(); > >> > >> /* Trace events are available after this */ > >> trace_init(); > >> diff --git a/kernel/rcu/prcu.c b/kernel/rcu/prcu.c > >> index a00b9420..f198285c 100644 > >> --- a/kernel/rcu/prcu.c > >> +++ b/kernel/rcu/prcu.c > >> @@ -1,11 +1,12 @@ > >> #include > >> -#include > >> #include > >> -#include > >> +#include > >> #include > >> - > >> +#include > >> #include > >> > >> +#include "rcu.h" > >> + > >> DEFINE_PER_CPU_SHARED_ALIGNED(struct prcu_local_struct, prcu_local); > >> > >> struct prcu_struct global_prcu = { > >> @@ -16,6 +17,16 @@ struct prcu_struct global_prcu = { > >> }; > >> struct prcu_struct *prcu = &global_prcu; > >> > >> +/* Initialize simple callback list. */ > >> +static void prcu_cblist_init(struct prcu_cblist *rclp) > >> +{ > >> + rclp->head = NULL; > >> + rclp->tail = &rclp->head; > >> + rclp->version_head = NULL; > >> + rclp->version_tail = &rclp->version_head; > >> + rclp->len = 0; > >> +} > >> + > >> static inline void prcu_report(struct prcu_local_struct *local) > >> { > >> unsigned long long global_version; > >> @@ -123,3 +134,53 @@ void prcu_note_context_switch(void) > >> prcu_report(local); > >> put_cpu_ptr(&prcu_local); > >> } > >> + > >> +void call_prcu(struct rcu_head *head, rcu_callback_t func) > >> +{ > >> + unsigned long flags; > >> + struct prcu_local_struct *local; > >> + struct prcu_cblist *rclp; > >> + struct prcu_version_head *vhp; > >> + > >> + debug_rcu_head_queue(head); > >> + > >> + /* Use GFP_ATOMIC with IRQs disabled */ > >> + vhp = kmalloc(sizeof(struct prcu_version_head), GFP_ATOMIC); > >> + if (!vhp) > >> + return; > > > > Silently failing to post the callback can cause system hangs. I suggest > > finding some way to avoid allocating on the call_prcu() code path. > > > > You're absolutely right. We were also thinking of changing the > function return type from void to int to indicate whether the memory > allocation is successful or not. Suppose that you are a user of such a function. When it returns indicating failure, what are you supposed to do? What would be the complexity of the resulting failure-handling code? Having it simply unconditionally succeed is much friendlier to the user, especially given that it is not all that hard to make it do so. Thanx, Paul