Re: [PATCH tip/tracing/markers] markers: simplify marker_set_format()

[Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>]

* Lai Jiangshan (laijs@cn.fujitsu.com) wrote:
> 
> current marker_set_format() is complex this patch simplify it, 
> and decrease the overhead of marker_update_probes().
> 

Yep, I think I did put the format string after the name \0, which was
rather tricky. I agree that such change makes the code more readable at
the expense of doing 2 allocations per marker rather than one, but
readability might be a good thing here.

Thanks !

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/marker.c b/kernel/marker.c
> index e49a9c5..ef43c86 100644
> --- a/kernel/marker.c
> +++ b/kernel/marker.c
> @@ -65,6 +65,7 @@ struct marker_entry {
>  	void *oldptr;
>  	int rcu_pending;
>  	unsigned char ptype:1;
> +	unsigned char format_allocated:1;
>  	char name[0];	/* Contains name'\0'format'\0' */
>  };
>  
> @@ -415,6 +416,7 @@ static struct marker_entry *add_marker(const char *name, const char *format)
>  	e->single.probe_private = NULL;
>  	e->multi = NULL;
>  	e->ptype = 0;
> +	e->format_allocated = 0;
>  	e->refcount = 0;
>  	e->rcu_pending = 0;
>  	hlist_add_head(&e->hlist, head);
> @@ -446,6 +448,8 @@ static int remove_marker(const char *name)
>  	if (e->single.func != __mark_empty_function)
>  		return -EBUSY;
>  	hlist_del(&e->hlist);
> +	if (e->format_allocated)
> +		kfree(e->format);
>  	/* Make sure the call_rcu has been executed */
>  	if (e->rcu_pending)
>  		rcu_barrier_sched();
> @@ -456,57 +460,34 @@ static int remove_marker(const char *name)
>  /*
>   * Set the mark_entry format to the format found in the element.
>   */
> -static int marker_set_format(struct marker_entry **entry, const char *format)
> +static int marker_set_format(struct marker_entry *entry, const char *format)
>  {
> -	struct marker_entry *e;
> -	size_t name_len = strlen((*entry)->name) + 1;
> -	size_t format_len = strlen(format) + 1;
> -
> -
> -	e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
> -			GFP_KERNEL);
> -	if (!e)
> +	entry->format = kstrdup(format, GFP_KERNEL);
> +	if (!entry->format)
>  		return -ENOMEM;
> -	memcpy(&e->name[0], (*entry)->name, name_len);
> -	e->format = &e->name[name_len];
> -	memcpy(e->format, format, format_len);
> -	if (strcmp(e->format, MARK_NOARGS) == 0)
> -		e->call = marker_probe_cb_noarg;
> -	else
> -		e->call = marker_probe_cb;
> -	e->single = (*entry)->single;
> -	e->multi = (*entry)->multi;
> -	e->ptype = (*entry)->ptype;
> -	e->refcount = (*entry)->refcount;
> -	e->rcu_pending = 0;
> -	hlist_add_before(&e->hlist, &(*entry)->hlist);
> -	hlist_del(&(*entry)->hlist);
> -	/* Make sure the call_rcu has been executed */
> -	if ((*entry)->rcu_pending)
> -		rcu_barrier_sched();
> -	kfree(*entry);
> -	*entry = e;
> +	entry->format_allocated = 1;
> +
>  	trace_mark(core_marker_format, "name %s format %s",
> -			e->name, e->format);
> +			entry->name, entry->format);
>  	return 0;
>  }
>  
>  /*
>   * Sets the probe callback corresponding to one marker.
>   */
> -static int set_marker(struct marker_entry **entry, struct marker *elem,
> +static int set_marker(struct marker_entry *entry, struct marker *elem,
>  		int active)
>  {
>  	int ret;
> -	WARN_ON(strcmp((*entry)->name, elem->name) != 0);
> +	WARN_ON(strcmp(entry->name, elem->name) != 0);
>  
> -	if ((*entry)->format) {
> -		if (strcmp((*entry)->format, elem->format) != 0) {
> +	if (entry->format) {
> +		if (strcmp(entry->format, elem->format) != 0) {
>  			printk(KERN_NOTICE
>  				"Format mismatch for probe %s "
>  				"(%s), marker (%s)\n",
> -				(*entry)->name,
> -				(*entry)->format,
> +				entry->name,
> +				entry->format,
>  				elem->format);
>  			return -EPERM;
>  		}
> @@ -522,34 +503,33 @@ static int set_marker(struct marker_entry **entry, struct marker *elem,
>  	 * pass from a "safe" callback (with argument) to an "unsafe"
>  	 * callback (does not set arguments).
>  	 */
> -	elem->call = (*entry)->call;
> +	elem->call = entry->call;
>  	/*
>  	 * Sanity check :
>  	 * We only update the single probe private data when the ptr is
>  	 * set to a _non_ single probe! (0 -> 1 and N -> 1, N != 1)
>  	 */
>  	WARN_ON(elem->single.func != __mark_empty_function
> -		&& elem->single.probe_private
> -		!= (*entry)->single.probe_private &&
> -		!elem->ptype);
> -	elem->single.probe_private = (*entry)->single.probe_private;
> +		&& elem->single.probe_private != entry->single.probe_private
> +		&& !elem->ptype);
> +	elem->single.probe_private = entry->single.probe_private;
>  	/*
>  	 * Make sure the private data is valid when we update the
>  	 * single probe ptr.
>  	 */
>  	smp_wmb();
> -	elem->single.func = (*entry)->single.func;
> +	elem->single.func = entry->single.func;
>  	/*
>  	 * We also make sure that the new probe callbacks array is consistent
>  	 * before setting a pointer to it.
>  	 */
> -	rcu_assign_pointer(elem->multi, (*entry)->multi);
> +	rcu_assign_pointer(elem->multi, entry->multi);
>  	/*
>  	 * Update the function or multi probe array pointer before setting the
>  	 * ptype.
>  	 */
>  	smp_wmb();
> -	elem->ptype = (*entry)->ptype;
> +	elem->ptype = entry->ptype;
>  	elem->state = active;
>  
>  	return 0;
> @@ -593,8 +573,7 @@ void marker_update_probe_range(struct marker *begin,
>  	for (iter = begin; iter < end; iter++) {
>  		mark_entry = get_marker(iter->name);
>  		if (mark_entry) {
> -			set_marker(&mark_entry, iter,
> -					!!mark_entry->refcount);
> +			set_marker(mark_entry, iter, !!mark_entry->refcount);
>  			/*
>  			 * ignore error, continue
>  			 */
> @@ -656,7 +635,7 @@ int marker_probe_register(const char *name, const char *format,
>  			ret = PTR_ERR(entry);
>  	} else if (format) {
>  		if (!entry->format)
> -			ret = marker_set_format(&entry, format);
> +			ret = marker_set_format(entry, format);
>  		else if (strcmp(entry->format, format))
>  			ret = -EPERM;
>  	}
> 
> 
> 
> 
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68