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Subject[PATCH 5/9] hw-breakpoints: Use overflow handler instead of the event callback
Date
struct perf_event::event callback was called when a breakpoint
triggers. But this is a rather opaque callback, pretty
tied-only to the breakpoint API and not really integrated into perf
as it triggers even when we don't overflow.

We prefer to use overflow_handler() as it fits into the perf events
rules, being called only when we overflow.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "K. Prasad" <prasad@linux.vnet.ibm.com>
---
arch/x86/kernel/hw_breakpoint.c | 5 ++---
arch/x86/kernel/ptrace.c | 9 ++++++---
include/linux/hw_breakpoint.h | 25 +++++++++++--------------
include/linux/perf_event.h | 13 +++++++------
kernel/hw_breakpoint.c | 17 +++++------------
kernel/perf_event.c | 24 +++++++++---------------
kernel/trace/trace_ksym.c | 5 +++--
samples/hw_breakpoint/data_breakpoint.c | 7 +++++--
8 files changed, 48 insertions(+), 57 deletions(-)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index d42f65a..05d5fec 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -362,8 +362,7 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp,
return ret;
}

- if (bp->callback)
- ret = arch_store_info(bp);
+ ret = arch_store_info(bp);

if (ret < 0)
return ret;
@@ -519,7 +518,7 @@ static int __kprobes hw_breakpoint_handler(struct die_args *args)
break;
}

- (bp->callback)(bp, args->regs);
+ perf_bp_event(bp, args->regs);

rcu_read_unlock();
}
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index dbb3955..b361d28 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -555,7 +555,9 @@ static int genregs_set(struct task_struct *target,
return ret;
}

-static void ptrace_triggered(struct perf_event *bp, void *data)
+static void ptrace_triggered(struct perf_event *bp, int nmi,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
{
int i;
struct thread_struct *thread = &(current->thread);
@@ -599,7 +601,7 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len, int type,
{
int err;
int gen_len, gen_type;
- DEFINE_BREAKPOINT_ATTR(attr);
+ struct perf_event_attr attr;

/*
* We shoud have at least an inactive breakpoint at this
@@ -721,9 +723,10 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
{
struct perf_event *bp;
struct thread_struct *t = &tsk->thread;
- DEFINE_BREAKPOINT_ATTR(attr);
+ struct perf_event_attr attr;

if (!t->ptrace_bps[nr]) {
+ hw_breakpoint_init(&attr);
/*
* Put stub len and type to register (reserve) an inactive but
* correct bp
diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index d33096e..4d14a38 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -20,19 +20,16 @@ enum {

#ifdef CONFIG_HAVE_HW_BREAKPOINT

-/* As it's for in-kernel or ptrace use, we want it to be pinned */
-#define DEFINE_BREAKPOINT_ATTR(name) \
-struct perf_event_attr name = { \
- .type = PERF_TYPE_BREAKPOINT, \
- .size = sizeof(name), \
- .pinned = 1, \
-};
-
static inline void hw_breakpoint_init(struct perf_event_attr *attr)
{
attr->type = PERF_TYPE_BREAKPOINT;
attr->size = sizeof(*attr);
+ /*
+ * As it's for in-kernel or ptrace use, we want it to be pinned
+ * and to call its callback every hits.
+ */
attr->pinned = 1;
+ attr->sample_period = 1;
}

static inline unsigned long hw_breakpoint_addr(struct perf_event *bp)
@@ -52,7 +49,7 @@ static inline int hw_breakpoint_len(struct perf_event *bp)

extern struct perf_event *
register_user_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered,
+ perf_overflow_handler_t triggered,
struct task_struct *tsk);

/* FIXME: only change from the attr, and don't unregister */
@@ -64,12 +61,12 @@ modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr);
*/
extern struct perf_event *
register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
- perf_callback_t triggered,
+ perf_overflow_handler_t triggered,
int cpu);

extern struct perf_event **
register_wide_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered);
+ perf_overflow_handler_t triggered);

extern int register_perf_hw_breakpoint(struct perf_event *bp);
extern int __register_perf_hw_breakpoint(struct perf_event *bp);
@@ -90,18 +87,18 @@ static inline struct arch_hw_breakpoint *counter_arch_bp(struct perf_event *bp)

static inline struct perf_event *
register_user_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered,
+ perf_overflow_handler_t triggered,
struct task_struct *tsk) { return NULL; }
static inline struct perf_event *
modify_user_hw_breakpoint(struct perf_event *bp,
struct perf_event_attr *attr) { return NULL; }
static inline struct perf_event *
register_wide_hw_breakpoint_cpu(struct perf_event_attr *attr,
- perf_callback_t triggered,
+ perf_overflow_handler_t triggered,
int cpu) { return NULL; }
static inline struct perf_event **
register_wide_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered) { return NULL; }
+ perf_overflow_handler_t triggered) { return NULL; }
static inline int
register_perf_hw_breakpoint(struct perf_event *bp) { return -ENOSYS; }
static inline int
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 84bd28a..d2f2667 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -565,10 +565,13 @@ struct perf_pending_entry {
void (*func)(struct perf_pending_entry *);
};

-typedef void (*perf_callback_t)(struct perf_event *, void *);
-
struct perf_sample_data;

+typedef void (*perf_callback_t)(struct perf_event *, void *);
+typedef void (*perf_overflow_handler_t)(struct perf_event *, int,
+ struct perf_sample_data *,
+ struct pt_regs *regs);
+
/**
* struct perf_event - performance event kernel representation:
*/
@@ -660,9 +663,7 @@ struct perf_event {
struct pid_namespace *ns;
u64 id;

- void (*overflow_handler)(struct perf_event *event,
- int nmi, struct perf_sample_data *data,
- struct pt_regs *regs);
+ perf_overflow_handler_t overflow_handler;

#ifdef CONFIG_EVENT_PROFILE
struct event_filter *filter;
@@ -779,7 +780,7 @@ extern struct perf_event *
perf_event_create_kernel_counter(struct perf_event_attr *attr,
int cpu,
pid_t pid,
- perf_callback_t callback);
+ perf_overflow_handler_t callback);
extern u64 perf_event_read_value(struct perf_event *event,
u64 *enabled, u64 *running);

diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index 2d10b01..b600fc2 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -259,7 +259,7 @@ void release_bp_slot(struct perf_event *bp)
}


-int __register_perf_hw_breakpoint(struct perf_event *bp)
+int register_perf_hw_breakpoint(struct perf_event *bp)
{
int ret;

@@ -276,19 +276,12 @@ int __register_perf_hw_breakpoint(struct perf_event *bp)
* This is a quick hack that will be removed soon, once we remove
* the tmp breakpoints from ptrace
*/
- if (!bp->attr.disabled || bp->callback == perf_bp_event)
+ if (!bp->attr.disabled || !bp->overflow_handler)
ret = arch_validate_hwbkpt_settings(bp, bp->ctx->task);

return ret;
}

-int register_perf_hw_breakpoint(struct perf_event *bp)
-{
- bp->callback = perf_bp_event;
-
- return __register_perf_hw_breakpoint(bp);
-}
-
/**
* register_user_hw_breakpoint - register a hardware breakpoint for user space
* @attr: breakpoint attributes
@@ -297,7 +290,7 @@ int register_perf_hw_breakpoint(struct perf_event *bp)
*/
struct perf_event *
register_user_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered,
+ perf_overflow_handler_t triggered,
struct task_struct *tsk)
{
return perf_event_create_kernel_counter(attr, -1, tsk->pid, triggered);
@@ -322,7 +315,7 @@ modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
unregister_hw_breakpoint(bp);

return perf_event_create_kernel_counter(attr, -1, bp->ctx->task->pid,
- bp->callback);
+ bp->overflow_handler);
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);

@@ -347,7 +340,7 @@ EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);
*/
struct perf_event **
register_wide_hw_breakpoint(struct perf_event_attr *attr,
- perf_callback_t triggered)
+ perf_overflow_handler_t triggered)
{
struct perf_event **cpu_events, **pevent, *bp;
long err;
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 6b7ddba..fd43ff4 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -4286,15 +4286,8 @@ static void bp_perf_event_destroy(struct perf_event *event)
static const struct pmu *bp_perf_event_init(struct perf_event *bp)
{
int err;
- /*
- * The breakpoint is already filled if we haven't created the counter
- * through perf syscall
- * FIXME: manage to get trigerred to NULL if it comes from syscalls
- */
- if (!bp->callback)
- err = register_perf_hw_breakpoint(bp);
- else
- err = __register_perf_hw_breakpoint(bp);
+
+ err = register_perf_hw_breakpoint(bp);
if (err)
return ERR_PTR(err);

@@ -4390,7 +4383,7 @@ perf_event_alloc(struct perf_event_attr *attr,
struct perf_event_context *ctx,
struct perf_event *group_leader,
struct perf_event *parent_event,
- perf_callback_t callback,
+ perf_overflow_handler_t overflow_handler,
gfp_t gfpflags)
{
const struct pmu *pmu;
@@ -4433,10 +4426,10 @@ perf_event_alloc(struct perf_event_attr *attr,

event->state = PERF_EVENT_STATE_INACTIVE;

- if (!callback && parent_event)
- callback = parent_event->callback;
+ if (!overflow_handler && parent_event)
+ overflow_handler = parent_event->overflow_handler;

- event->callback = callback;
+ event->overflow_handler = overflow_handler;

if (attr->disabled)
event->state = PERF_EVENT_STATE_OFF;
@@ -4776,7 +4769,8 @@ err_put_context:
*/
struct perf_event *
perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
- pid_t pid, perf_callback_t callback)
+ pid_t pid,
+ perf_overflow_handler_t overflow_handler)
{
struct perf_event *event;
struct perf_event_context *ctx;
@@ -4793,7 +4787,7 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
}

event = perf_event_alloc(attr, cpu, ctx, NULL,
- NULL, callback, GFP_KERNEL);
+ NULL, overflow_handler, GFP_KERNEL);
if (IS_ERR(event)) {
err = PTR_ERR(event);
goto err_put_context;
diff --git a/kernel/trace/trace_ksym.c b/kernel/trace/trace_ksym.c
index ddfa0fd..acb87d4 100644
--- a/kernel/trace/trace_ksym.c
+++ b/kernel/trace/trace_ksym.c
@@ -79,11 +79,12 @@ void ksym_collect_stats(unsigned long hbp_hit_addr)
}
#endif /* CONFIG_PROFILE_KSYM_TRACER */

-void ksym_hbp_handler(struct perf_event *hbp, void *data)
+void ksym_hbp_handler(struct perf_event *hbp, int nmi,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
{
struct ring_buffer_event *event;
struct ksym_trace_entry *entry;
- struct pt_regs *regs = data;
struct ring_buffer *buffer;
int pc;

diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index 2952550..c69cbe9 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -41,7 +41,9 @@ module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
" write operations on the kernel symbol");

-static void sample_hbp_handler(struct perf_event *temp, void *data)
+static void sample_hbp_handler(struct perf_event *bp, int nmi,
+ struct perf_sample_data *data,
+ struct pt_regs *regs)
{
printk(KERN_INFO "%s value is changed\n", ksym_name);
dump_stack();
@@ -51,8 +53,9 @@ static void sample_hbp_handler(struct perf_event *temp, void *data)
static int __init hw_break_module_init(void)
{
int ret;
- DEFINE_BREAKPOINT_ATTR(attr);
+ struct perf_event_attr attr;

+ hw_breakpoint_init(&attr);
attr.bp_addr = kallsyms_lookup_name(ksym_name);
attr.bp_len = HW_BREAKPOINT_LEN_4;
attr.bp_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
--
1.6.2.3


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