Re: [for-next][PATCH 7/7] tracing: Use pr_err() instead of WARN() for memory failures

[Joe Perches]

On Sun, 2020-01-26 at 14:19 -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> 
> As warnings can trigger panics, especially when "panic_on_warn" is set,
> memory failure warnings can cause panics and fail fuzz testers that are
> stressing memory.
> 
> Create a MEM_FAIL() macro to use instead of WARN() in the tracing code
> (perhaps this should be a kernel wide macro?), and use that for memory
> failure issues. This should stop failing fuzz tests due to warnings.

It looks as if most of these could just be removed instead
as there is an existing dump_stack() on failure.

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
[]
> @@ -5459,7 +5459,7 @@ static void __init set_ftrace_early_graph(char *buf, int enable)
>  	struct ftrace_hash *hash;
>  
>  	hash = alloc_ftrace_hash(FTRACE_HASH_DEFAULT_BITS);
> -	if (WARN_ON(!hash))
> +	if (MEM_FAIL(!hash, "Failed to allocate hash\n"))
>  		return;

has dump_stack()
 
>  	while (buf) {
> @@ -6591,7 +6591,7 @@ static void add_to_clear_hash_list(struct list_head *clear_list,
>  
>  	func = kmalloc(sizeof(*func), GFP_KERNEL);
>  	if (!func) {
> -		WARN_ONCE(1, "alloc failure, ftrace filter could be stale\n");
> +		MEM_FAIL(1, "alloc failure, ftrace filter could be stale\n");

has dump_stack()

> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
[]
> @@ -3126,7 +3126,7 @@ static int alloc_percpu_trace_buffer(void)
>  	struct trace_buffer_struct *buffers;
>  
>  	buffers = alloc_percpu(struct trace_buffer_struct);
> -	if (WARN(!buffers, "Could not allocate percpu trace_printk buffer"))
> +	if (MEM_FAIL(!buffers, "Could not allocate percpu trace_printk buffer"))
>  		return -ENOMEM;

has dump_stack()

>  
>  	trace_percpu_buffer = buffers;
> @@ -7932,7 +7932,7 @@ static struct dentry *tracing_dentry_percpu(struct trace_array *tr, int cpu)
>  
>  	tr->percpu_dir = tracefs_create_dir("per_cpu", d_tracer);
>  
> -	WARN_ONCE(!tr->percpu_dir,
> +	MEM_FAIL(!tr->percpu_dir,
>  		  "Could not create tracefs directory 'per_cpu/%d'\n", cpu);

keep?
 
>  	return tr->percpu_dir;
> @@ -8253,7 +8253,7 @@ create_trace_option_files(struct trace_array *tr, struct tracer *tracer)
>  	for (cnt = 0; opts[cnt].name; cnt++) {
>  		create_trace_option_file(tr, &topts[cnt], flags,
>  					 &opts[cnt]);
> -		WARN_ONCE(topts[cnt].entry == NULL,
> +		MEM_FAIL(topts[cnt].entry == NULL,
>  			  "Failed to create trace option: %s",
>  			  opts[cnt].name);
>  	}
> @@ -8437,7 +8437,7 @@ static int allocate_trace_buffers(struct trace_array *tr, int size)
>  #ifdef CONFIG_TRACER_MAX_TRACE
>  	ret = allocate_trace_buffer(tr, &tr->max_buffer,
>  				    allocate_snapshot ? size : 1);
> -	if (WARN_ON(ret)) {
> +	if (MEM_FAIL(ret, "Failed to allocate trace buffer\n")) {
>  		ring_buffer_free(tr->array_buffer.buffer);
>  		tr->array_buffer.buffer = NULL;
>  		free_percpu(tr->array_buffer.data);
> @@ -8726,7 +8726,7 @@ static __init void create_trace_instances(struct dentry *d_tracer)
>  	trace_instance_dir = tracefs_create_instance_dir("instances", d_tracer,
>  							 instance_mkdir,
>  							 instance_rmdir);
> -	if (WARN_ON(!trace_instance_dir))
> +	if (MEM_FAIL(!trace_instance_dir, "Failed to create instances directory\n"))
>  		return;
>  }
>  
> @@ -8796,7 +8796,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
>  #endif
>  
>  	if (ftrace_create_function_files(tr, d_tracer))
> -		WARN(1, "Could not allocate function filter files");
> +		MEM_FAIL(1, "Could not allocate function filter files");
>  
>  #ifdef CONFIG_TRACER_SNAPSHOT
>  	trace_create_file("snapshot", 0644, d_tracer,
> @@ -9348,8 +9348,7 @@ __init static int tracer_alloc_buffers(void)
>  
>  	/* TODO: make the number of buffers hot pluggable with CPUS */
>  	if (allocate_trace_buffers(&global_trace, ring_buf_size) < 0) {
> -		printk(KERN_ERR "tracer: failed to allocate ring buffer!\n");
> -		WARN_ON(1);
> +		MEM_FAIL(1, "tracer: failed to allocate ring buffer!\n");

has dump_stack()

>  		goto out_free_savedcmd;
>  	}
>  
> @@ -9422,7 +9421,8 @@ void __init early_trace_init(void)
>  	if (tracepoint_printk) {
>  		tracepoint_print_iter =
>  			kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
> -		if (WARN_ON(!tracepoint_print_iter))
> +		if (MEM_FAIL(!tracepoint_print_iter,
> +			     "Failed to allocate trace iterator\n"))

has dump_stack()

>  			tracepoint_printk = 0;
>  		else
>  			static_key_enable(&tracepoint_printk_key.key);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 4812a36affac..6bb64d89c321 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -94,6 +94,18 @@ enum trace_type {
>  
>  #include "trace_entries.h"
>  
> +/* Use this for memory failure errors */
> +#define MEM_FAIL(condition, fmt, ...) ({			\
> +	static bool __section(.data.once) __warned;		\
> +	int __ret_warn_once = !!(condition);			\
> +								\
> +	if (unlikely(__ret_warn_once && !__warned)) {		\
> +		__warned = true;				\
> +		pr_err("ERROR: " fmt, ##__VA_ARGS__);		\
> +	}							\
> +	unlikely(__ret_warn_once);				\
> +})
> +
>  /*
>   * syscalls are special, and need special handling, this is why
>   * they are not included in trace_entries.h