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SubjectRe: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe
On 07/17, Steven Rostedt wrote:
>
> On Tue, 2013-07-16 at 15:38 -0400, Steven Rostedt wrote:
>
> > > Btw, Steven, what about other pending (and orthogonal changes) ?
> > > >From Jovi, from me. I see nothing new in linux-trace.git#for-next...
> >
> > My INBOX is full with too much crap. I thought I grabbed the patches
> > from you and Jovi, but they may have been something else.
> >
> > Can you just tell me what the subjects were. My INBOX currently has
> > >10,000 emails, and it's just getting worse.

Please see the attached mbox. It contains 2 series with
perf_trace_buf/perf_xxx hacks.

1-3 looks very simple and straightforward.

4-6 reimplement TP_perf_assign(), we already discussed this (and you even
did the performance testing), but I am still not sure if you agree with
this hack or not.

And 2 patches from Jovi, acked by Masami and me:

[PATCH 1/2 v6] tracing/uprobes: Support ftrace_event_file base multibuffer
[PATCH 2/2 v6] tracing/uprobes: Support soft-mode disabling

Oleg.
From aa40385bba7692f4b53572da24119c3b293c9aa1 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 17 Jun 2013 19:02:04 +0200
Subject: [PATCH 1/6] tracing/function: Avoid perf_trace_buf_*() if event_function.perf_events is empty

perf_trace_buf_prepare() + perf_trace_buf_submit(head, task => NULL)
make no sense if hlist_empty(head). Change perf_ftrace_function_call()
to check event_function.perf_events beforehand.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/trace/trace_event_perf.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 84b1e04..12df557 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -266,6 +266,10 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
struct pt_regs regs;
int rctx;

+ head = this_cpu_ptr(event_function.perf_events);
+ if (hlist_empty(head))
+ return;
+
#define ENTRY_SIZE (ALIGN(sizeof(struct ftrace_entry) + sizeof(u32), \
sizeof(u64)) - sizeof(u32))

@@ -279,8 +283,6 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,

entry->ip = ip;
entry->parent_ip = parent_ip;
-
- head = this_cpu_ptr(event_function.perf_events);
perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, 0,
1, &regs, head, NULL);

--
1.5.5.1

From 803ce880302ef7d21bdad2196cddc76b4c1a49a1 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 17 Jun 2013 19:02:07 +0200
Subject: [PATCH 2/6] tracing/syscall: Avoid perf_trace_buf_*() if sys_data->perf_events is empty

perf_trace_buf_prepare() + perf_trace_buf_submit(head, task => NULL)
make no sense if hlist_empty(head). Change perf_syscall_enter/exit()
to check sys_data->{enter,exit}_event->perf_events beforehand.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/trace/trace_syscalls.c | 12 ++++++++----
1 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 322e164..ea5b672 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -566,6 +566,10 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
if (!sys_data)
return;

+ head = this_cpu_ptr(sys_data->enter_event->perf_events);
+ if (hlist_empty(head))
+ return;
+
/* get the size after alignment with the u32 buffer size field */
size = sizeof(unsigned long) * sys_data->nb_args + sizeof(*rec);
size = ALIGN(size + sizeof(u32), sizeof(u64));
@@ -583,8 +587,6 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
rec->nr = syscall_nr;
syscall_get_arguments(current, regs, 0, sys_data->nb_args,
(unsigned long *)&rec->args);
-
- head = this_cpu_ptr(sys_data->enter_event->perf_events);
perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
}

@@ -642,6 +644,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
if (!sys_data)
return;

+ head = this_cpu_ptr(sys_data->exit_event->perf_events);
+ if (hlist_empty(head))
+ return;
+
/* We can probably do that at build time */
size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
size -= sizeof(u32);
@@ -661,8 +667,6 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)

rec->nr = syscall_nr;
rec->ret = syscall_get_return_value(current, regs);
-
- head = this_cpu_ptr(sys_data->exit_event->perf_events);
perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
}

--
1.5.5.1

From 6037b2b9af2e6122380e967406f89ae9410fc5d6 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Mon, 17 Jun 2013 19:02:11 +0200
Subject: [PATCH 3/6] tracing/perf: Move the PERF_MAX_TRACE_SIZE check into perf_trace_buf_prepare()

Every perf_trace_buf_prepare() caller does
WARN_ONCE(size > PERF_MAX_TRACE_SIZE, message) and "message" is
almost the same.
Shift this WARN_ONCE() into perf_trace_buf_prepare(). This changes
the meaning of _ONCE, but I think this is fine.

- 4947014 2932448 10104832 17984294 1126b26 vmlinux
+ 4948422 2932448 10104832 17985702 11270a6 vmlinux

on my build.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/trace/ftrace.h | 4 ----
kernel/trace/trace_event_perf.c | 4 ++++
kernel/trace/trace_kprobe.c | 6 ------
kernel/trace/trace_syscalls.c | 12 ------------
kernel/trace/trace_uprobe.c | 2 --
5 files changed, 4 insertions(+), 24 deletions(-)
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 19edd7f..c162a57 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -666,10 +666,6 @@ perf_trace_##call(void *__data, proto) \
sizeof(u64)); \
__entry_size -= sizeof(u32); \
\
- if (WARN_ONCE(__entry_size > PERF_MAX_TRACE_SIZE, \
- "profile buffer not large enough")) \
- return; \
- \
entry = (struct ftrace_raw_##call *)perf_trace_buf_prepare( \
__entry_size, event_call->event.type, &__regs, &rctx); \
if (!entry) \
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 12df557..80c36bc 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -236,6 +236,10 @@ __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,

BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));

+ if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
+ "perf buffer not large enough"))
+ return NULL;
+
pc = preempt_count();

*rctxp = perf_swevent_get_recursion_context();
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 7ed6976..ae6ce83 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1087,9 +1087,6 @@ kprobe_perf_func(struct trace_probe *tp, struct pt_regs *regs)
__size = sizeof(*entry) + tp->size + dsize;
size = ALIGN(__size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);
- if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
- "profile buffer not large enough"))
- return;

entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
if (!entry)
@@ -1120,9 +1117,6 @@ kretprobe_perf_func(struct trace_probe *tp, struct kretprobe_instance *ri,
__size = sizeof(*entry) + tp->size + dsize;
size = ALIGN(__size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);
- if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
- "profile buffer not large enough"))
- return;

entry = perf_trace_buf_prepare(size, call->event.type, regs, &rctx);
if (!entry)
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index ea5b672..b7e3447 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -575,10 +575,6 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
size = ALIGN(size + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

- if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
- "perf buffer not large enough"))
- return;
-
rec = (struct syscall_trace_enter *)perf_trace_buf_prepare(size,
sys_data->enter_event->event.type, regs, &rctx);
if (!rec)
@@ -652,14 +648,6 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
size -= sizeof(u32);

- /*
- * Impossible, but be paranoid with the future
- * How to put this check outside runtime?
- */
- if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
- "exit event has grown above perf buffer size"))
- return;
-
rec = (struct syscall_trace_exit *)perf_trace_buf_prepare(size,
sys_data->exit_event->event.type, regs, &rctx);
if (!rec)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index d5d0cd3..a23d2d7 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -818,8 +818,6 @@ static void uprobe_perf_print(struct trace_uprobe *tu,

size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
size = ALIGN(size + tu->size + sizeof(u32), sizeof(u64)) - sizeof(u32);
- if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE, "profile buffer not large enough"))
- return;

preempt_disable();
head = this_cpu_ptr(call->perf_events);
--
1.5.5.1

From f883693f6e02a9c5c1e32b47490671ffa554a6fe Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 18 Jun 2013 21:22:11 +0200
Subject: [PATCH 4/6] tracing/perf: expand TRACE_EVENT(sched_stat_runtime)

To simplify the review of the next patch:

1. We are going to reimplent __perf_task/counter and embedd them
into TP_ARGS(). expand TRACE_EVENT(sched_stat_runtime) into
DECLARE_EVENT_CLASS() + DEFINE_EVENT(), this way they can use
different TP_ARGS's.

2. Change perf_trace_##call() macri to do perf_fetch_caller_regs()
right before perf_trace_buf_prepare(). This way it evaluates
"args" asap.

Note: after 87f44bbc perf_trace_buf_prepare() doesn't need
"struct pt_regs *regs", perhaps it makes sense to remove this
argument. And perhaps we can teach perf_trace_buf_submit()
to accept regs == NULL and do fetch_caller_regs(CALLER_ADDR1)
in this case.

3. Cosmetic, but the typecast from "void*" buys nothing. It just
adds the noise, remove it.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/trace/events/sched.h | 6 +++++-
include/trace/ftrace.h | 7 +++----
2 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index e5586ca..249c024 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -372,7 +372,7 @@ DEFINE_EVENT(sched_stat_template, sched_stat_blocked,
* Tracepoint for accounting runtime (time the task is executing
* on a CPU).
*/
-TRACE_EVENT(sched_stat_runtime,
+DECLARE_EVENT_CLASS(sched_stat_runtime,

TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),

@@ -401,6 +401,10 @@ TRACE_EVENT(sched_stat_runtime,
(unsigned long long)__entry->vruntime)
);

+DEFINE_EVENT(sched_stat_runtime, sched_stat_runtime,
+ TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),
+ TP_ARGS(tsk, runtime, vruntime));
+
/*
* Tracepoint for showing priority inheritance modifying a tasks
* priority.
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index c162a57..aed594a 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -659,15 +659,14 @@ perf_trace_##call(void *__data, proto) \
int __data_size; \
int rctx; \
\
- perf_fetch_caller_regs(&__regs); \
- \
__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
sizeof(u64)); \
__entry_size -= sizeof(u32); \
\
- entry = (struct ftrace_raw_##call *)perf_trace_buf_prepare( \
- __entry_size, event_call->event.type, &__regs, &rctx); \
+ perf_fetch_caller_regs(&__regs); \
+ entry = perf_trace_buf_prepare(__entry_size, \
+ event_call->event.type, &__regs, &rctx); \
if (!entry) \
return; \
\
--
1.5.5.1

From 74318b1e89e7d6e6de9bb4992ab41e761c1175f6 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 18 Jun 2013 21:22:14 +0200
Subject: [PATCH 5/6] tracing/perf: reimplement TP_perf_assign() logic

TP_perf_assign/__perf_xxx is used to change the default values
of __addr/__count/__task variables for perf_trace_buf_submit().

Unfortunately, TP_perf_assign() is called "too late", we want to
have a fast-path "__task != NULL" check in perf_trace_##call() at
the start. So this patch simply embeds __perf_xxx() into TP_ARGS(),
this way DECLARE_EVENT_CLASS() can use the result of assignments
hidden in "args" right after ftrace_get_offsets_##call() which is
mostly trivial.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/trace/events/sched.h | 16 +++-------------
include/trace/ftrace.h | 19 +++++++++++--------
2 files changed, 14 insertions(+), 21 deletions(-)
diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
index 249c024..2e7d994 100644
--- a/include/trace/events/sched.h
+++ b/include/trace/events/sched.h
@@ -57,7 +57,7 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,

TP_PROTO(struct task_struct *p, int success),

- TP_ARGS(p, success),
+ TP_ARGS(__perf_task(p), success),

TP_STRUCT__entry(
__array( char, comm, TASK_COMM_LEN )
@@ -73,9 +73,6 @@ DECLARE_EVENT_CLASS(sched_wakeup_template,
__entry->prio = p->prio;
__entry->success = success;
__entry->target_cpu = task_cpu(p);
- )
- TP_perf_assign(
- __perf_task(p);
),

TP_printk("comm=%s pid=%d prio=%d success=%d target_cpu=%03d",
@@ -313,7 +310,7 @@ DECLARE_EVENT_CLASS(sched_stat_template,

TP_PROTO(struct task_struct *tsk, u64 delay),

- TP_ARGS(tsk, delay),
+ TP_ARGS(__perf_task(tsk), __perf_count(delay)),

TP_STRUCT__entry(
__array( char, comm, TASK_COMM_LEN )
@@ -325,10 +322,6 @@ DECLARE_EVENT_CLASS(sched_stat_template,
memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
__entry->pid = tsk->pid;
__entry->delay = delay;
- )
- TP_perf_assign(
- __perf_count(delay);
- __perf_task(tsk);
),

TP_printk("comm=%s pid=%d delay=%Lu [ns]",
@@ -376,7 +369,7 @@ DECLARE_EVENT_CLASS(sched_stat_runtime,

TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),

- TP_ARGS(tsk, runtime, vruntime),
+ TP_ARGS(tsk, __perf_count(runtime), vruntime),

TP_STRUCT__entry(
__array( char, comm, TASK_COMM_LEN )
@@ -390,9 +383,6 @@ DECLARE_EVENT_CLASS(sched_stat_runtime,
__entry->pid = tsk->pid;
__entry->runtime = runtime;
__entry->vruntime = vruntime;
- )
- TP_perf_assign(
- __perf_count(runtime);
),

TP_printk("comm=%s pid=%d runtime=%Lu [ns] vruntime=%Lu [ns]",
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index aed594a..8886877 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -503,8 +503,14 @@ static inline notrace int ftrace_get_offsets_##call( \
#undef TP_fast_assign
#define TP_fast_assign(args...) args

-#undef TP_perf_assign
-#define TP_perf_assign(args...)
+#undef __perf_addr
+#define __perf_addr(a) (a)
+
+#undef __perf_count
+#define __perf_count(c) (c)
+
+#undef __perf_task
+#define __perf_task(t) (t)

#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
@@ -632,16 +638,13 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
#define __get_str(field) (char *)__get_dynamic_array(field)

#undef __perf_addr
-#define __perf_addr(a) __addr = (a)
+#define __perf_addr(a) (__addr = (a))

#undef __perf_count
-#define __perf_count(c) __count = (c)
+#define __perf_count(c) (__count = (c))

#undef __perf_task
-#define __perf_task(t) __task = (t)
-
-#undef TP_perf_assign
-#define TP_perf_assign(args...) args
+#define __perf_task(t) (__task = (t))

#undef DECLARE_EVENT_CLASS
#define DECLARE_EVENT_CLASS(call, proto, args, tstruct, assign, print) \
--
1.5.5.1

From f5e6c3976bd68a72d7259e3282c5fda20fcefa4c Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 18 Jun 2013 21:22:18 +0200
Subject: [PATCH 6/6] tracing/perf: Avoid perf_trace_buf_*() in perf_trace_##call() when possible

perf_trace_buf_prepare() + perf_trace_buf_submit(task => NULL)
make no sense if hlist_empty(head). Change perf_trace_##call()
to check ->perf_events beforehand and do nothing if it is empty.

However, we can only do this if __task == NULL, so we also add
the __builtin_constant_p(__task) check.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
include/trace/ftrace.h | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 8886877..04455b8 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -663,6 +663,12 @@ perf_trace_##call(void *__data, proto) \
int rctx; \
\
__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
+ \
+ head = this_cpu_ptr(event_call->perf_events); \
+ if (__builtin_constant_p(!__task) && !__task && \
+ hlist_empty(head)) \
+ return; \
+ \
__entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),\
sizeof(u64)); \
__entry_size -= sizeof(u32); \
@@ -677,7 +683,6 @@ perf_trace_##call(void *__data, proto) \
\
{ assign; } \
\
- head = this_cpu_ptr(event_call->perf_events); \
perf_trace_buf_submit(entry, __entry_size, rctx, __addr, \
__count, &__regs, head, __task); \
}
--
1.5.5.1
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