[RFC PATCH 3/9] fprobe: Add nr_maxactive to specify rethook_node pool size

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add nr_maxactive to specify rethook_node pool size. This means
the maximum number of actively running target functions concurrently
for probing by exit_handler. Note that if the running function is
preempted or sleep, it is still counted as 'active'.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 include/linux/fprobe.h |    2 ++
 kernel/trace/fprobe.c  |    5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/fprobe.h b/include/linux/fprobe.h
index e0d4e6136249..678f741a7b33 100644
--- a/include/linux/fprobe.h
+++ b/include/linux/fprobe.h
@@ -14,6 +14,7 @@
  * @flags: The status flag.
  * @rethook: The rethook data structure. (internal data)
  * @entry_data_size: The private data storage size.
+ * @nr_maxactive: The max number of active functions.
  * @entry_handler: The callback function for function entry.
  * @exit_handler: The callback function for function exit.
  */
@@ -31,6 +32,7 @@ struct fprobe {
 	unsigned int		flags;
 	struct rethook		*rethook;
 	size_t			entry_data_size;
+	int			nr_maxactive;
 
 	void (*entry_handler)(struct fprobe *fp, unsigned long entry_ip,
 			      struct pt_regs *regs, void *entry_data);
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index fa25d09c9d57..f222848571f2 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -143,7 +143,10 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
 	}
 
 	/* Initialize rethook if needed */
-	size = num * num_possible_cpus() * 2;
+	if (fp->nr_maxactive)
+		size = fp->nr_maxactive;
+	else
+		size = num * num_possible_cpus() * 2;
 	if (size < 0)
 		return -E2BIG;