tracing/kprobes: Turn trace_probe->files into list_head

I think that "ftrace_event_file *trace_probe[]" complicates the
code for no reason, turn it into list_head to simplify the code.
enable_trace_probe() no longer needs synchronize_sched().

This needs the extra sizeof(list_head) memory for every attached
ftrace_event_file, hopefully not a problem in this case.

Link: http://lkml.kernel.org/r/20130620173814.GA13165@redhat.com
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 282f86cfd30451d7cb23ca57cebbd7875c305202..405b5b0f903e9b6ec192ab5acd3b893dbabbaa94 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -35,12 +35,17 @@ struct trace_probe {
        const char              *symbol;        /* symbol name */
        struct ftrace_event_class       class;
        struct ftrace_event_call        call;
-       struct ftrace_event_file * __rcu *files;
+       struct list_head        files;
        ssize_t                 size;           /* trace entry size */
        unsigned int            nr_args;
        struct probe_arg        args[];
 };
 
+struct event_file_link {
+       struct ftrace_event_file        *file;
+       struct list_head                list;
+};
+
 #define SIZEOF_TRACE_PROBE(n)                  \
        (offsetof(struct trace_probe, args) +   \
        (sizeof(struct probe_arg) * (n)))
@@ -150,6 +155,7 @@ static struct trace_probe *alloc_trace_probe(const char *group,
                goto error;
 
        INIT_LIST_HEAD(&tp->list);
+       INIT_LIST_HEAD(&tp->files);
        return tp;
 error:
        kfree(tp->call.name);
@@ -183,22 +189,6 @@ static struct trace_probe *find_trace_probe(const char *event,
        return NULL;
 }
 
-/*
- * This and enable_trace_probe/disable_trace_probe rely on event_mutex
- * held by the caller, __ftrace_set_clr_event().
- */
-static int trace_probe_nr_files(struct trace_probe *tp)
-{
-       struct ftrace_event_file **file = rcu_dereference_raw(tp->files);
-       int ret = 0;
-
-       if (file)
-               while (*(file++))
-                       ret++;
-
-       return ret;
-}
-
 /*
  * Enable trace_probe
  * if the file is NULL, enable "perf" handler, or enable "trace" handler.
@@ -209,29 +199,18 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
        int ret = 0;
 
        if (file) {
-               struct ftrace_event_file **new, **old;
-               int n = trace_probe_nr_files(tp);
-
-               old = rcu_dereference_raw(tp->files);
-               /* 1 is for new one and 1 is for stopper */
-               new = kzalloc((n + 2) * sizeof(struct ftrace_event_file *),
-                             GFP_KERNEL);
-               if (!new) {
+               struct event_file_link *link;
+
+               link = kmalloc(sizeof(*link), GFP_KERNEL);
+               if (!link) {
                        ret = -ENOMEM;
                        goto out;
                }
-               memcpy(new, old, n * sizeof(struct ftrace_event_file *));
-               new[n] = file;
-               /* The last one keeps a NULL */
 
-               rcu_assign_pointer(tp->files, new);
-               tp->flags |= TP_FLAG_TRACE;
+               link->file = file;
+               list_add_tail_rcu(&link->list, &tp->files);
 
-               if (old) {
-                       /* Make sure the probe is done with old files */
-                       synchronize_sched();
-                       kfree(old);
-               }
+               tp->flags |= TP_FLAG_TRACE;
        } else
                tp->flags |= TP_FLAG_PROFILE;
 
@@ -245,24 +224,16 @@ enable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
        return ret;
 }
 
-static int
-trace_probe_file_index(struct trace_probe *tp, struct ftrace_event_file *file)
+static struct event_file_link *
+find_event_file_link(struct trace_probe *tp, struct ftrace_event_file *file)
 {
-       struct ftrace_event_file **files;
-       int i;
+       struct event_file_link *link;
 
-       /*
-        * Since all tp->files updater is protected by probe_enable_lock,
-        * we don't need to lock an rcu_read_lock.
-        */
-       files = rcu_dereference_raw(tp->files);
-       if (files) {
-               for (i = 0; files[i]; i++)
-                       if (files[i] == file)
-                               return i;
-       }
+       list_for_each_entry(link, &tp->files, list)
+               if (link->file == file)
+                       return link;
 
-       return -1;
+       return NULL;
 }
 
 /*
@@ -275,38 +246,23 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
        int ret = 0;
 
        if (file) {
-               struct ftrace_event_file **new, **old;
-               int n = trace_probe_nr_files(tp);
-               int i, j;
+               struct event_file_link *link;
 
-               old = rcu_dereference_raw(tp->files);
-               if (n == 0 || trace_probe_file_index(tp, file) < 0) {
+               link = find_event_file_link(tp, file);
+               if (!link) {
                        ret = -EINVAL;
                        goto out;
                }
 
-               if (n == 1) {   /* Remove the last file */
-                       tp->flags &= ~TP_FLAG_TRACE;
-                       new = NULL;
-               } else {
-                       new = kzalloc(n * sizeof(struct ftrace_event_file *),
-                                     GFP_KERNEL);
-                       if (!new) {
-                               ret = -ENOMEM;
-                               goto out;
-                       }
-
-                       /* 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];
-               }
+               list_del_rcu(&link->list);
+               /* synchronize with kprobe_trace_func/kretprobe_trace_func */
+               synchronize_sched();
+               kfree(link);
 
-               rcu_assign_pointer(tp->files, new);
+               if (!list_empty(&tp->files))
+                       goto out;
 
-               /* Make sure the probe is done with old files */
-               synchronize_sched();
-               kfree(old);
+               tp->flags &= ~TP_FLAG_TRACE;
        } else
                tp->flags &= ~TP_FLAG_PROFILE;
 
@@ -871,20 +827,10 @@ __kprobe_trace_func(struct trace_probe *tp, struct pt_regs *regs,
 static __kprobes void
 kprobe_trace_func(struct trace_probe *tp, struct pt_regs *regs)
 {
-       /*
-        * Note: preempt is already disabled around the kprobe handler.
-        * However, we still need an smp_read_barrier_depends() corresponding
-        * to smp_wmb() in rcu_assign_pointer() to access the pointer.
-        */
-       struct ftrace_event_file **file = rcu_dereference_raw(tp->files);
-
-       if (unlikely(!file))
-               return;
+       struct event_file_link *link;
 
-       while (*file) {
-               __kprobe_trace_func(tp, regs, *file);
-               file++;
-       }
+       list_for_each_entry_rcu(link, &tp->files, list)
+               __kprobe_trace_func(tp, regs, link->file);
 }
 
 /* Kretprobe handler */
@@ -931,20 +877,10 @@ static __kprobes void
 kretprobe_trace_func(struct trace_probe *tp, struct kretprobe_instance *ri,
                     struct pt_regs *regs)
 {
-       /*
-        * Note: preempt is already disabled around the kprobe handler.
-        * However, we still need an smp_read_barrier_depends() corresponding
-        * to smp_wmb() in rcu_assign_pointer() to access the pointer.
-        */
-       struct ftrace_event_file **file = rcu_dereference_raw(tp->files);
-
-       if (unlikely(!file))
-               return;
+       struct event_file_link *link;
 
-       while (*file) {
-               __kretprobe_trace_func(tp, ri, regs, *file);
-               file++;
-       }
+       list_for_each_entry_rcu(link, &tp->files, list)
+               __kretprobe_trace_func(tp, ri, regs, link->file);
 }
 
 /* Event entry printers */