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Message-ID: <20130614162112.GO5146@linux.vnet.ibm.com>
Date: Fri, 14 Jun 2013 09:21:12 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
"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>
Subject: Re: [PATCH] tracing/uprobes: Support ftrace_event_file base
multibuffer
On Fri, Jun 14, 2013 at 11:31:58AM -0400, Steven Rostedt wrote:
> 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.
If irqs and preempt are disabled, I suggest using rcu_dereference_sched().
That is what it is there for. ;-)
Thanx, Paul
> -- 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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