by Namhyung Kim

[permalink] [raw]

Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

Hi Jovi,

[SNIP]

On Tue, 3 Sep 2013 19:10:04 +0800, zhangwei wrote:
>> + if (atomic_inc_return(&uprobe_buffer_ref) == 1) {
>> + int cpu;
>> +
>> + uprobe_cpu_buffer = __alloc_percpu(PAGE_SIZE, PAGE_SIZE);
>> + if (uprobe_cpu_buffer == NULL)
>> + return -ENOMEM;
>> +
>
> Do we need add atomic_dec if allocate percpu buffer failed?

Good catch! I'll fix it. :)

Thanks,
Namhyung

>
>> + for_each_possible_cpu(cpu)
>> + mutex_init(&per_cpu(uprobe_cpu_mutex, cpu));
>> + }
>> +
>> WARN_ON(!uprobe_filter_is_empty(&tu->filter));

2013-09-04 08:13:52

by Namhyung Kim

[permalink] [raw]

Subject: [PATCH v5.1 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

From: Namhyung Kim <[email protected]>

Fetching from user space should be done in a non-atomic context. So
use a per-cpu buffer and copy its content to the ring buffer
atomically. Note that we can migrate during accessing user memory
thus use a per-cpu mutex to protect concurrent accesses.

This is needed since we'll be able to fetch args from an user memory
which can be swapped out. Before that uprobes could fetch args from
registers only which saved in a kernel space.

While at it, use __get_data_size() and store_trace_args() to reduce
code duplication.

Reviewed-by: Masami Hiramatsu <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: zhangwei(Jovi) <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
---
kernel/trace/trace_uprobe.c | 98 +++++++++++++++++++++++++++++++++++++--------
1 file changed, 82 insertions(+), 16 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 9f2d12d2311d..c32f8f2ddc11 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -530,21 +530,44 @@ static const struct file_operations uprobe_profile_ops = {
.release = seq_release,
};

+static atomic_t uprobe_buffer_ref = ATOMIC_INIT(0);
+static void __percpu *uprobe_cpu_buffer;
+static DEFINE_PER_CPU(struct mutex, uprobe_cpu_mutex);
+
static void uprobe_trace_print(struct trace_uprobe *tu,
unsigned long func, struct pt_regs *regs)
{
struct uprobe_trace_entry_head *entry;
struct ring_buffer_event *event;
struct ring_buffer *buffer;
- void *data;
- int size, i;
+ struct mutex *mutex;
+ void *data, *arg_buf;
+ int size, dsize, esize;
+ int cpu;
struct ftrace_event_call *call = &tu->p.call;

- size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
+ dsize = __get_data_size(&tu->p, regs);
+ esize = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
+
+ if (WARN_ON_ONCE(!uprobe_cpu_buffer || tu->p.size + dsize > PAGE_SIZE))
+ return;
+
+ cpu = raw_smp_processor_id();
+ mutex = &per_cpu(uprobe_cpu_mutex, cpu);
+ arg_buf = per_cpu_ptr(uprobe_cpu_buffer, cpu);
+
+ /*
+ * Use per-cpu buffers for fastest access, but we might migrate
+ * so the mutex makes sure we have sole access to it.
+ */
+ mutex_lock(mutex);
+ store_trace_args(esize, &tu->p, regs, arg_buf, dsize);
+
+ size = esize + tu->p.size + dsize;
event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
- size + tu->p.size, 0, 0);
+ size, 0, 0);
if (!event)
- return;
+ goto out;

entry = ring_buffer_event_data(event);
if (is_ret_probe(tu)) {
@@ -556,13 +579,13 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
data = DATAOF_TRACE_ENTRY(entry, false);
}

- for (i = 0; i < tu->p.nr_args; i++) {
- call_fetch(&tu->p.args[i].fetch, regs,
- data + tu->p.args[i].offset);
- }
+ memcpy(data, arg_buf, tu->p.size + dsize);

if (!filter_current_check_discard(buffer, call, entry, event))
trace_buffer_unlock_commit(buffer, event, 0, 0);
+
+out:
+ mutex_unlock(mutex);
}

/* uprobe handler */
@@ -630,6 +653,19 @@ probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
if (trace_probe_is_enabled(&tu->p))
return -EINTR;

+ if (atomic_inc_return(&uprobe_buffer_ref) == 1) {
+ int cpu;
+
+ uprobe_cpu_buffer = __alloc_percpu(PAGE_SIZE, PAGE_SIZE);
+ if (uprobe_cpu_buffer == NULL) {
+ atomic_dec(&uprobe_buffer_ref);
+ return -ENOMEM;
+ }
+
+ for_each_possible_cpu(cpu)
+ mutex_init(&per_cpu(uprobe_cpu_mutex, cpu));
+ }
+
WARN_ON(!uprobe_filter_is_empty(&tu->filter));

tu->p.flags |= flag;
@@ -646,6 +682,11 @@ static void probe_event_disable(struct trace_uprobe *tu, int flag)
if (!trace_probe_is_enabled(&tu->p))
return;

+ if (atomic_dec_and_test(&uprobe_buffer_ref)) {
+ free_percpu(uprobe_cpu_buffer);
+ uprobe_cpu_buffer = NULL;
+ }
+
WARN_ON(!uprobe_filter_is_empty(&tu->filter));

uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
@@ -776,11 +817,33 @@ static void uprobe_perf_print(struct trace_uprobe *tu,
struct ftrace_event_call *call = &tu->p.call;
struct uprobe_trace_entry_head *entry;
struct hlist_head *head;
- void *data;
- int size, rctx, i;
+ struct mutex *mutex;
+ void *data, *arg_buf;
+ int size, dsize, esize;
+ int cpu;
+ int rctx;

- size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
- size = ALIGN(size + tu->p.size + sizeof(u32), sizeof(u64)) - sizeof(u32);
+ dsize = __get_data_size(&tu->p, regs);
+ esize = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
+
+ if (WARN_ON_ONCE(!uprobe_cpu_buffer))
+ return;
+
+ size = esize + tu->p.size + dsize;
+ size = ALIGN(size + sizeof(u32), sizeof(u64)) - sizeof(u32);
+ if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE, "profile buffer not large enough"))
+ return;
+
+ cpu = raw_smp_processor_id();
+ mutex = &per_cpu(uprobe_cpu_mutex, cpu);
+ arg_buf = per_cpu_ptr(uprobe_cpu_buffer, cpu);
+
+ /*
+ * Use per-cpu buffers for fastest access, but we might migrate
+ * so the mutex makes sure we have sole access to it.
+ */
+ mutex_lock(mutex);
+ store_trace_args(esize, &tu->p, regs, arg_buf, dsize);

preempt_disable();
head = this_cpu_ptr(call->perf_events);
@@ -800,15 +863,18 @@ static void uprobe_perf_print(struct trace_uprobe *tu,
data = DATAOF_TRACE_ENTRY(entry, false);
}

- for (i = 0; i < tu->p.nr_args; i++) {
- struct probe_arg *parg = &tu->p.args[i];
+ memcpy(data, arg_buf, tu->p.size + dsize);
+
+ if (size - esize > tu->p.size + dsize) {
+ int len = tu->p.size + dsize;

- call_fetch(&parg->fetch, regs, data + parg->offset);
+ memset(data + len, 0, size - esize - len);
}

perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
out:
preempt_enable();
+ mutex_unlock(mutex);
}

/* uprobe profile handler */
--
1.7.11.7