From 2d542cf34264ac92e9e7ac55c0b096b066d569d2 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Wed, 25 Feb 2009 08:40:09 +0100 Subject: [PATCH] tracing/hw-branch-tracing: convert bts-tracer mutex to a spinlock Impact: fix CPU hotplug lockup bts_hotcpu_handler() is called with irqs disabled, so using mutex_lock() is a no-no. All the BTS codepaths here are atomic (they do not schedule), so using a spinlock is the right solution. Cc: Markus Metzger Signed-off-by: Ingo Molnar --- kernel/trace/trace_hw_branches.c | 57 ++++++++++++++++---------------- 1 file changed, 28 insertions(+), 29 deletions(-) diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c index 3335e807144..7bfdf4c2347 100644 --- a/kernel/trace/trace_hw_branches.c +++ b/kernel/trace/trace_hw_branches.c @@ -3,17 +3,15 @@ * * Copyright (C) 2008-2009 Intel Corporation. * Markus Metzger , 2008-2009 - * */ - -#include -#include +#include +#include #include #include -#include -#include +#include #include #include +#include #include @@ -23,16 +21,17 @@ #define SIZEOF_BTS (1 << 13) -/* The tracer mutex protects the below per-cpu tracer array. - It needs to be held to: - - start tracing on all cpus - - stop tracing on all cpus - - start tracing on a single hotplug cpu - - stop tracing on a single hotplug cpu - - read the trace from all cpus - - read the trace from a single cpu -*/ -static DEFINE_MUTEX(bts_tracer_mutex); +/* + * The tracer lock protects the below per-cpu tracer array. + * It needs to be held to: + * - start tracing on all cpus + * - stop tracing on all cpus + * - start tracing on a single hotplug cpu + * - stop tracing on a single hotplug cpu + * - read the trace from all cpus + * - read the trace from a single cpu + */ +static DEFINE_SPINLOCK(bts_tracer_lock); static DEFINE_PER_CPU(struct bts_tracer *, tracer); static DEFINE_PER_CPU(unsigned char[SIZEOF_BTS], buffer); @@ -47,7 +46,7 @@ static struct trace_array *hw_branch_trace __read_mostly; * Start tracing on the current cpu. * The argument is ignored. * - * pre: bts_tracer_mutex must be locked. + * pre: bts_tracer_lock must be locked. */ static void bts_trace_start_cpu(void *arg) { @@ -66,19 +65,19 @@ static void bts_trace_start_cpu(void *arg) static void bts_trace_start(struct trace_array *tr) { - mutex_lock(&bts_tracer_mutex); + spin_lock(&bts_tracer_lock); on_each_cpu(bts_trace_start_cpu, NULL, 1); trace_hw_branches_enabled = 1; - mutex_unlock(&bts_tracer_mutex); + spin_unlock(&bts_tracer_lock); } /* * Stop tracing on the current cpu. * The argument is ignored. * - * pre: bts_tracer_mutex must be locked. + * pre: bts_tracer_lock must be locked. */ static void bts_trace_stop_cpu(void *arg) { @@ -90,12 +89,12 @@ static void bts_trace_stop_cpu(void *arg) static void bts_trace_stop(struct trace_array *tr) { - mutex_lock(&bts_tracer_mutex); + spin_lock(&bts_tracer_lock); trace_hw_branches_enabled = 0; on_each_cpu(bts_trace_stop_cpu, NULL, 1); - mutex_unlock(&bts_tracer_mutex); + spin_unlock(&bts_tracer_lock); } static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb, @@ -103,7 +102,7 @@ static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb, { unsigned int cpu = (unsigned long)hcpu; - mutex_lock(&bts_tracer_mutex); + spin_lock(&bts_tracer_lock); if (!trace_hw_branches_enabled) goto out; @@ -119,7 +118,7 @@ static int __cpuinit bts_hotcpu_handler(struct notifier_block *nfb, } out: - mutex_unlock(&bts_tracer_mutex); + spin_unlock(&bts_tracer_lock); return NOTIFY_DONE; } @@ -225,7 +224,7 @@ static void trace_bts_at(const struct bts_trace *trace, void *at) /* * Collect the trace on the current cpu and write it into the ftrace buffer. * - * pre: bts_tracer_mutex must be locked + * pre: bts_tracer_lock must be locked */ static void trace_bts_cpu(void *arg) { @@ -261,11 +260,11 @@ out: static void trace_bts_prepare(struct trace_iterator *iter) { - mutex_lock(&bts_tracer_mutex); + spin_lock(&bts_tracer_lock); on_each_cpu(trace_bts_cpu, iter->tr, 1); - mutex_unlock(&bts_tracer_mutex); + spin_unlock(&bts_tracer_lock); } static void trace_bts_close(struct trace_iterator *iter) @@ -275,11 +274,11 @@ static void trace_bts_close(struct trace_iterator *iter) void trace_hw_branch_oops(void) { - mutex_lock(&bts_tracer_mutex); + spin_lock(&bts_tracer_lock); trace_bts_cpu(hw_branch_trace); - mutex_unlock(&bts_tracer_mutex); + spin_unlock(&bts_tracer_lock); } struct tracer bts_tracer __read_mostly = -- 2.41.1