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Message-ID: <5225C38C.2090305@huawei.com>
Date: Tue, 3 Sep 2013 19:10:04 +0800
From: "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>
To: Namhyung Kim <namhyung@...nel.org>
CC: Steven Rostedt <rostedt@...dmis.org>,
Namhyung Kim <namhyung.kim@....com>,
Hyeoncheol Lee <cheol.lee@....com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
LKML <linux-kernel@...r.kernel.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Oleg Nesterov <oleg@...hat.com>,
Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a
ring buffer
On 2013/9/3 13:44, Namhyung Kim wrote:
> From: Namhyung Kim <namhyung.kim@....com>
>
> 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.
>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: zhangwei(Jovi) <jovi.zhangwei@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> kernel/trace/trace_uprobe.c | 97 +++++++++++++++++++++++++++++++++++++--------
> 1 file changed, 81 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 9f2d12d2311d..9ede401759ab 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -530,21 +530,46 @@ 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);
> - if (!event)
> + size, 0, 0);
> + if (!event) {
> + mutex_unlock(mutex);
> return;
> + }
>
> entry = ring_buffer_event_data(event);
> if (is_ret_probe(tu)) {
> @@ -556,13 +581,12 @@ 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);
> +
> + mutex_unlock(mutex);
> }
>
> /* uprobe handler */
> @@ -630,6 +654,17 @@ 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)
> + return -ENOMEM;
> +
Do we need add atomic_dec if allocate percpu buffer failed?
> + 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 +681,11 @@ 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 +816,33 @@ 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 +862,18 @@ 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 */
>
--
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