tracing: Fix hwlat kthread migration

The hwlat tracer creates a kernel thread at start of the tracer. It is
pinned to a single CPU and will move to the next CPU after each period of
running. If the user modifies the migration thread's affinity, it will not
change after that happens.

The original code created the thread at the first instance it was called,
but later was changed to destroy the thread after the tracer was finished,
and would not be created until the next instance of the tracer was
established. The code that initialized the affinity was only called on the
initial instantiation of the tracer. After that, it was not initialized, and
the previous affinity did not match the current newly created one, making
it appear that the user modified the thread's affinity when it did not, and
the thread failed to migrate again.

Cc: stable@vger.kernel.org
Fixes: 0330f7aa8ee6 ("tracing: Have hwlat trace migrate across tracing_cpumask CPUs")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

path: root/dev.h

#ifndef DEV_H
#define DEV_H

#include <sys/socket.h>
#include "built_in.h"

extern size_t device_mtu(const char *ifname);
extern int device_address(const char *ifname, int af, struct sockaddr_storage *ss);
extern int __device_ifindex(const char *ifname);
extern int device_ifindex(const char *ifname);
extern int device_type(const char *ifname);
extern short device_get_flags(const char *ifname);
extern void device_set_flags(const char *ifname, const short flags);
extern int device_up_and_running(const char *ifname);
extern u32 device_bitrate(const char *ifname);
extern short device_enter_promiscuous_mode(const char *ifname);
extern void device_leave_promiscuous_mode(const char *ifname, short oldflags);
extern const char *device_type2str(uint16_t type);
extern const char *device_addr2str(const unsigned char *addr, int alen, int type,
				   char *buf, int blen);
#endif /* DEV_H */