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[94.245.46.61]) by smtp.gmail.com with ESMTPSA id c16sm2045676lfb.36.2021.02.28.11.47.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 28 Feb 2021 11:47:02 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Sun, 28 Feb 2021 20:47:00 +0100 To: Sangmoon Kim , neeraju@codeaurora.org, paulmck@kernel.org Cc: neeraju@codeaurora.org, jiangshanlai@gmail.com, joel@joelfernandes.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, paulmck@kernel.org, rcu@vger.kernel.org, rostedt@goodmis.org Subject: Re: [PATCH v2] rcu/tree: Add a trace event for RCU stall warnings Message-ID: <20210228194700.GA55724@pc638.lan> References: <20210224151711.7823-1-sangmoon.kim@samsung.com> <20210225040612.9917-1-sangmoon.kim@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210225040612.9917-1-sangmoon.kim@samsung.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org > The event allows us to trace the RCU stall when > sysctl_panic_on_rcu_stall is disabled. > > The first parameter is the name of RCU flavour like other trace > events. The second one shows us which function detected stalls. > > The RCU stall is mainly caused by external factors such as interrupt > handling or task scheduling or something else. Therefore, this event > uses TRACE_EVENT macro, not dedicated one, so that someone interested > in the RCU stall can use it without CONFIG_RCU_TRACE. > > Signed-off-by: Sangmoon Kim > --- > Changes in v2: > - Move the tracepoints before printing out stall messages. > > include/trace/events/rcu.h | 28 ++++++++++++++++++++++++++++ > kernel/rcu/tree_exp.h | 1 + > kernel/rcu/tree_stall.h | 2 ++ > 3 files changed, 31 insertions(+) > > diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h > index 155b5cb43cfd..8476f3161bd0 100644 > --- a/include/trace/events/rcu.h > +++ b/include/trace/events/rcu.h > @@ -432,6 +432,34 @@ TRACE_EVENT_RCU(rcu_fqs, > __entry->cpu, __entry->qsevent) > ); > > +/* > + * Tracepoint for RCU stall events. Takes a string identifying the RCU flavor > + * and a string identifying which function detected the RCU stall as follows: > + * > + * "StallDetected": Scheduler-tick detects other CPU's stalls. > + * "SelfDetected": Scheduler-tick detects a current CPU's stall. > + * "ExpeditedStall": Expedited grace period detects stalls. > + */ > +TRACE_EVENT(rcu_stall_warning, > + > + TP_PROTO(const char *rcuname, const char *msg), > + > + TP_ARGS(rcuname, msg), > + > + TP_STRUCT__entry( > + __field(const char *, rcuname) > + __field(const char *, msg) > + ), > + > + TP_fast_assign( > + __entry->rcuname = rcuname; > + __entry->msg = msg; > + ), > + > + TP_printk("%s %s", > + __entry->rcuname, __entry->msg) > +); > + > #endif /* #if defined(CONFIG_TREE_RCU) */ > > /* > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index 8760b6ead770..6e1ac5b41f69 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -521,6 +521,7 @@ static void synchronize_rcu_expedited_wait(void) > if (rcu_stall_is_suppressed()) > continue; > panic_on_rcu_stall(); > + trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall")); > pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", > rcu_state.name); > ndetected = 0; > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h > index 70d48c52fabc..ed50056a3c7b 100644 > --- a/kernel/rcu/tree_stall.h > +++ b/kernel/rcu/tree_stall.h > @@ -488,6 +488,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) > * See Documentation/RCU/stallwarn.rst for info on how to debug > * RCU CPU stall warnings. > */ > + trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected")); > pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); > rcu_for_each_leaf_node(rnp) { > raw_spin_lock_irqsave_rcu_node(rnp, flags); > @@ -554,6 +555,7 @@ static void print_cpu_stall(unsigned long gps) > * See Documentation/RCU/stallwarn.rst for info on how to debug > * RCU CPU stall warnings. > */ > + trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected")); > pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name); > raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags); > print_cpu_stall_info(smp_processor_id()); > -- > 2.17.1 > One small nit, the patch is not cleanelly applied on latest dev so it should be rebased unless Paul fixes it on his own :) Anyway to me it looks OK. Reviewed-by: Uladzislau Rezki (Sony) -- Vlad Rezki