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/include/net/hwbm.h

#ifndef _HWBM_H
#define _HWBM_H

struct hwbm_pool {
	/* Capacity of the pool */
	int size;
	/* Size of the buffers managed */
	int frag_size;
	/* Number of buffers currently used by this pool */
	int buf_num;
	/* constructor called during alocation */
	int (*construct)(struct hwbm_pool *bm_pool, void *buf);
	/* protect acces to the buffer counter*/
	spinlock_t lock;
	/* private data */
	void *priv;
};
#ifdef CONFIG_HWBM
void hwbm_buf_free(struct hwbm_pool *bm_pool, void *buf);
int hwbm_pool_refill(struct hwbm_pool *bm_pool, gfp_t gfp);
int hwbm_pool_add(struct hwbm_pool *bm_pool, unsigned int buf_num, gfp_t gfp);
#else
void hwbm_buf_free(struct hwbm_pool *bm_pool, void *buf) {}
int hwbm_pool_refill(struct hwbm_pool *bm_pool, gfp_t gfp) { return 0; }
int hwbm_pool_add(struct hwbm_pool *bm_pool, unsigned int buf_num, gfp_t gfp)
{ return 0; }
#endif /* CONFIG_HWBM */
#endif /* _HWBM_H */