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Message-ID: <1371223918.9844.324.camel@gandalf.local.home>
Date: Fri, 14 Jun 2013 11:31:58 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: "zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>,
Oleg Nesterov <oleg@...hat.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"yrl.pp-manager.tt@...achi.com" <yrl.pp-manager.tt@...achi.com>,
"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH] tracing/uprobes: Support ftrace_event_file base
multibuffer
On Fri, 2013-06-14 at 22:21 +0900, Masami Hiramatsu wrote:
> (2013/06/14 10:44), zhangwei(Jovi) wrote:
> > Support multi-buffer on uprobe-based dynamic events by
> > using ftrace_event_file.
> >
> > The code change is based on kprobe-based dynamic events
> > multibuffer support work commited by Masami(commit 41a7dd420c)
>
> I'm not so sure that rcu_dereference_raw() can ensure the safety
> of accessing pointer in uprobe handler. ( since kprobes disables
> irq and preempt, it could use rcu.)
Correct.
>
> Srikar, Oleg, could you check that?
>
> Thank you,
>
> >
> > Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@...wei.com>
> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Oleg Nesterov <oleg@...hat.com>
> > Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> > ---
> > kernel/trace/trace_uprobe.c | 183 +++++++++++++++++++++++++++++++++++++------
> > 1 file changed, 161 insertions(+), 22 deletions(-)
> >
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index d5d0cd3..31f08d6 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -53,6 +53,7 @@ struct trace_uprobe {
> > struct list_head list;
> > struct ftrace_event_class class;
> > struct ftrace_event_call call;
> > + struct ftrace_event_file * __rcu *files;
> > struct trace_uprobe_filter filter;
> > struct uprobe_consumer consumer;
> > struct inode *inode;
> > @@ -513,7 +514,8 @@ static const struct file_operations uprobe_profile_ops = {
> > };
> >
> > static void uprobe_trace_print(struct trace_uprobe *tu,
> > - unsigned long func, struct pt_regs *regs)
> > + unsigned long func, struct pt_regs *regs,
> > + struct ftrace_event_file *ftrace_file)
> > {
> > struct uprobe_trace_entry_head *entry;
> > struct ring_buffer_event *event;
> > @@ -522,9 +524,15 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
> > int size, i;
> > struct ftrace_event_call *call = &tu->call;
> >
> > + WARN_ON(call != ftrace_file->event_call);
> > +
> > + if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
> > + return;
> > +
> > size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
> > - event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
> > - size + tu->size, 0, 0);
> > + event = trace_event_buffer_lock_reserve(&buffer, ftrace_file,
> > + call->event.type,
> > + size + tu->size, 0, 0);
> > if (!event)
> > return;
> >
> > @@ -548,15 +556,35 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
> > /* uprobe handler */
> > static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
> > {
> > - if (!is_ret_probe(tu))
> > - uprobe_trace_print(tu, 0, regs);
> > + struct ftrace_event_file **file;
> > +
> > + if (is_ret_probe(tu))
> > + return 0;
> > +
> > + file = rcu_dereference_raw(tu->files);
Why are you using rcu_dereference_raw() and not rcu_dereference(). The
_raw() is a bit special, and unless you know what you are doing with RCU
here, don't use it.
As I see you using rcu_dereference_raw() all over this patch, along with
mutexes, I believe that you are not using RCU correctly here.
-- Steve
> > + if (unlikely(!file))
> > + return 0;
> > +
> > + while (*file) {
> > + uprobe_trace_print(tu, 0, regs, *file);
> > + file++;
> > + }
> > +
> > return 0;
> > }
> >
> > static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
> > struct pt_regs *regs)
> > {
> > - uprobe_trace_print(tu, func, regs);
> > + struct ftrace_event_file **file = rcu_dereference_raw(tu->files);
> > +
> > + if (unlikely(!file))
> > + return;
> > +
> > + while (*file) {
> > + uprobe_trace_print(tu, func, regs, *file);
> > + file++;
> > + }
> > }
> >
> > /* Event entry printers */
> > @@ -597,6 +625,26 @@ partial:
> > return TRACE_TYPE_PARTIAL_LINE;
> > }
> >
> > +
> > +static int trace_uprobe_nr_files(struct trace_uprobe *tu)
> > +{
> > + struct ftrace_event_file **file;
> > + int ret = 0;
> > +
> > + /*
> > + * Since all tu->files updater is protected by uprobe_enable_lock,
> > + * we don't need to lock an rcu_read_lock.
> > + */
> > + file = rcu_dereference_raw(tu->files);
> > + if (file)
> > + while (*(file++))
> > + ret++;
> > +
> > + return ret;
> > +}
> > +
> > +static DEFINE_MUTEX(uprobe_enable_lock);
> > +
> > static inline bool is_trace_uprobe_enabled(struct trace_uprobe *tu)
> > {
> > return tu->flags & (TP_FLAG_TRACE | TP_FLAG_PROFILE);
> > @@ -607,33 +655,123 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> > struct mm_struct *mm);
> >
> > static int
> > -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> > +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> > + filter_func_t filter)
> > {
> > + int enabled = 0;
> > int ret = 0;
> >
> > + mutex_lock(&uprobe_enable_lock);
> > +
> > if (is_trace_uprobe_enabled(tu))
> > - return -EINTR;
> > + enabled = 1;
> > +
> > + if (file) {
> > + struct ftrace_event_file **new, **old;
> > + int n = trace_uprobe_nr_files(tu);
> > +
> > + old = rcu_dereference_raw(tu->files);
> > + /* 1 is for new one and 1 is for stopper */
> > + new = kzalloc((n + 2) * sizeof(struct ftrace_event_file *),
> > + GFP_KERNEL);
> > + if (!new) {
> > + ret = -ENOMEM;
> > + goto out_unlock;
> > + }
> > + memcpy(new, old, n * sizeof(struct ftrace_event_file *));
> > + new[n] = file;
> > + /* The last one keeps a NULL */
> > +
> > + rcu_assign_pointer(tu->files, new);
> > + tu->flags |= TP_FLAG_TRACE;
> > +
> > + if (old) {
> > + /* Make sure the probe is done with old files */
> > + synchronize_sched();
> > + kfree(old);
> > + }
> > + } else
> > + tu->flags |= TP_FLAG_PROFILE;
> >
> > WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> >
> > - tu->flags |= flag;
> > - tu->consumer.filter = filter;
> > - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > - if (ret)
> > - tu->flags &= ~flag;
> > + if (!enabled) {
> > + tu->consumer.filter = filter;
> > + ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > + if (ret)
> > + tu->flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
> > + }
> >
> > + out_unlock:
> > + mutex_unlock(&uprobe_enable_lock);
> > return ret;
> > }
> >
> > -static void probe_event_disable(struct trace_uprobe *tu, int flag)
> > +static int
> > +trace_uprobe_file_index(struct trace_uprobe *tu, struct ftrace_event_file *file)
> > {
> > - if (!is_trace_uprobe_enabled(tu))
> > - return;
> > + struct ftrace_event_file **files;
> > + int i;
> > +
> > + /*
> > + * Since all tu->files updater is protected by uprobe_enable_lock,
> > + * we don't need to lock an rcu_read_lock.
> > + */
> > + files = rcu_dereference_raw(tu->files);
> > + if (files) {
> > + for (i = 0; files[i]; i++)
> > + if (files[i] == file)
> > + return i;
> > + }
> > +
> > + return -1;
> > +}
> > +
> > +static void
> > +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
> > +{
> > + mutex_lock(&uprobe_enable_lock);
> > +
> > + if (file) {
> > + struct ftrace_event_file **new, **old;
> > + int n = trace_uprobe_nr_files(tu);
> > + int i, j;
> > +
> > + old = rcu_dereference_raw(tu->files);
> > + if (n == 0 || trace_uprobe_file_index(tu, file) < 0)
> > + goto out_unlock;
> > +
> > + if (n == 1) { /* Remove the last file */
> > + tu->flags &= ~TP_FLAG_TRACE;
> > + new = NULL;
> > + } else {
> > + new = kzalloc(n * sizeof(struct ftrace_event_file *),
> > + GFP_KERNEL);
> > + if (!new)
> > + goto out_unlock;
> > +
> > + /* This copy & check loop copies the NULL stopper too */
> > + for (i = 0, j = 0; j < n && i < n + 1; i++)
> > + if (old[i] != file)
> > + new[j++] = old[i];
> > + }
> > +
> > + rcu_assign_pointer(tu->files, new);
> > +
> > + /* Make sure the probe is done with old files */
> > + synchronize_sched();
> > + kfree(old);
> > + } else
> > + tu->flags &= ~TP_FLAG_PROFILE;
> > +
> >
> > WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> >
> > - uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> > - tu->flags &= ~flag;
> > + if (!is_trace_uprobe_enabled(tu))
> > + uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> > +
> > + out_unlock:
> > + mutex_unlock(&uprobe_enable_lock);
> > }
> >
> > static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
> > @@ -869,21 +1007,22 @@ static
> > int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type, void *data)
> > {
> > struct trace_uprobe *tu = event->data;
> > + struct ftrace_event_file *file = data;
> >
> > switch (type) {
> > case TRACE_REG_REGISTER:
> > - return probe_event_enable(tu, TP_FLAG_TRACE, NULL);
> > + return probe_event_enable(tu, file, NULL);
> >
> > case TRACE_REG_UNREGISTER:
> > - probe_event_disable(tu, TP_FLAG_TRACE);
> > + probe_event_disable(tu, file);
> > return 0;
> >
> > #ifdef CONFIG_PERF_EVENTS
> > case TRACE_REG_PERF_REGISTER:
> > - return probe_event_enable(tu, TP_FLAG_PROFILE, uprobe_perf_filter);
> > + return probe_event_enable(tu, NULL, uprobe_perf_filter);
> >
> > case TRACE_REG_PERF_UNREGISTER:
> > - probe_event_disable(tu, TP_FLAG_PROFILE);
> > + probe_event_disable(tu, NULL);
> > return 0;
> >
> > case TRACE_REG_PERF_OPEN:
> >
>
>
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