Commit c2489bb7 authored by Zheng Yejian's avatar Zheng Yejian Committed by Steven Rostedt (Google)
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tracing: Introduce pipe_cpumask to avoid race on trace_pipes 

There is race issue when concurrently splice_read main trace_pipe and
per_cpu trace_pipes which will result in data read out being different
from what actually writen.

As suggested by Steven:
  > I believe we should add a ref count to trace_pipe and the per_cpu
  > trace_pipes, where if they are opened, nothing else can read it.
  >
  > Opening trace_pipe locks all per_cpu ref counts, if any of them are
  > open, then the trace_pipe open will fail (and releases any ref counts
  > it had taken).
  >
  > Opening a per_cpu trace_pipe will up the ref count for just that
  > CPU buffer. This will allow multiple tasks to read different per_cpu
  > trace_pipe files, but will prevent the main trace_pipe file from
  > being opened.

But because we only need to know whether per_cpu trace_pipe is open or
not, using a cpumask instead of using ref count may be easier.

After this patch, users will find that:
 - Main trace_pipe can be opened by only one user, and if it is
   opened, all per_cpu trace_pipes cannot be opened;
 - Per_cpu trace_pipes can be opened by multiple users, but each per_cpu
   trace_pipe can only be opened by one user. And if one of them is
   opened, main trace_pipe cannot be opened.

Link: https://lore.kernel.org/linux-trace-kernel/20230818022645.1948314-1-zhengyejian1@huawei.com



Suggested-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: default avatarZheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent eecb91b9

kernel/trace/trace.c

+48 −7
Original line number Diff line number Diff line
@@ -6718,10 +6718,36 @@ tracing_max_lat_write(struct file *filp, const char __user *ubuf, 


#endif



static int open_pipe_on_cpu(struct trace_array *tr, int cpu)

{

	if (cpu == RING_BUFFER_ALL_CPUS) {

		if (cpumask_empty(tr->pipe_cpumask)) {

			cpumask_setall(tr->pipe_cpumask);

			return 0;

		}

	} else if (!cpumask_test_cpu(cpu, tr->pipe_cpumask)) {

		cpumask_set_cpu(cpu, tr->pipe_cpumask);

		return 0;

	}

	return -EBUSY;

}



static void close_pipe_on_cpu(struct trace_array *tr, int cpu)

{

	if (cpu == RING_BUFFER_ALL_CPUS) {

		WARN_ON(!cpumask_full(tr->pipe_cpumask));

		cpumask_clear(tr->pipe_cpumask);

	} else {

		WARN_ON(!cpumask_test_cpu(cpu, tr->pipe_cpumask));

		cpumask_clear_cpu(cpu, tr->pipe_cpumask);

	}

}



static int tracing_open_pipe(struct inode *inode, struct file *filp)

{

	struct trace_array *tr = inode->i_private;

	struct trace_iterator *iter;

	int cpu;

	int ret;



	ret = tracing_check_open_get_tr(tr);
@@ -6729,13 +6755,16 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) 
		return ret;



	mutex_lock(&trace_types_lock);

	cpu = tracing_get_cpu(inode);

	ret = open_pipe_on_cpu(tr, cpu);

	if (ret)

		goto fail_pipe_on_cpu;



	/* create a buffer to store the information to pass to userspace */

	iter = kzalloc(sizeof(*iter), GFP_KERNEL);

	if (!iter) {

		ret = -ENOMEM;

		__trace_array_put(tr);

		goto out;

		goto fail_alloc_iter;

	}



	trace_seq_init(&iter->seq);
@@ -6758,7 +6787,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) 


	iter->tr = tr;

	iter->array_buffer = &tr->array_buffer;

	iter->cpu_file = tracing_get_cpu(inode);

	iter->cpu_file = cpu;

	mutex_init(&iter->mutex);

	filp->private_data = iter;
@@ -6768,12 +6797,15 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp) 
	nonseekable_open(inode, filp);



	tr->trace_ref++;

out:



	mutex_unlock(&trace_types_lock);

	return ret;



fail:

	kfree(iter);

fail_alloc_iter:

	close_pipe_on_cpu(tr, cpu);

fail_pipe_on_cpu:

	__trace_array_put(tr);

	mutex_unlock(&trace_types_lock);

	return ret;
@@ -6790,7 +6822,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file) 


	if (iter->trace->pipe_close)

		iter->trace->pipe_close(iter);



	close_pipe_on_cpu(tr, iter->cpu_file);

	mutex_unlock(&trace_types_lock);



	free_cpumask_var(iter->started);
@@ -9454,6 +9486,9 @@ static struct trace_array *trace_array_create(const char *name) 
	if (!alloc_cpumask_var(&tr->tracing_cpumask, GFP_KERNEL))

		goto out_free_tr;



	if (!alloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL))

		goto out_free_tr;



	tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS;



	cpumask_copy(tr->tracing_cpumask, cpu_all_mask);
@@ -9495,6 +9530,7 @@ static struct trace_array *trace_array_create(const char *name) 
 out_free_tr:

	ftrace_free_ftrace_ops(tr);

	free_trace_buffers(tr);

	free_cpumask_var(tr->pipe_cpumask);

	free_cpumask_var(tr->tracing_cpumask);

	kfree(tr->name);

	kfree(tr);
@@ -9597,6 +9633,7 @@ static int __remove_instance(struct trace_array *tr) 
	}

	kfree(tr->topts);



	free_cpumask_var(tr->pipe_cpumask);

	free_cpumask_var(tr->tracing_cpumask);

	kfree(tr->name);

	kfree(tr);
@@ -10394,12 +10431,14 @@ __init static int tracer_alloc_buffers(void) 
	if (trace_create_savedcmd() < 0)

		goto out_free_temp_buffer;



	if (!alloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL))

		goto out_free_savedcmd;



	/* TODO: make the number of buffers hot pluggable with CPUS */

	if (allocate_trace_buffers(&global_trace, ring_buf_size) < 0) {

		MEM_FAIL(1, "tracer: failed to allocate ring buffer!\n");

		goto out_free_savedcmd;

		goto out_free_pipe_cpumask;

	}



	if (global_trace.buffer_disabled)

		tracing_off();
@@ -10452,6 +10491,8 @@ __init static int tracer_alloc_buffers(void) 


	return 0;



out_free_pipe_cpumask:

	free_cpumask_var(global_trace.pipe_cpumask);

out_free_savedcmd:

	free_saved_cmdlines_buffer(savedcmd);

out_free_temp_buffer:

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -377,6 +377,8 @@ struct trace_array { 
	struct list_head	events;

	struct trace_event_file *trace_marker_file;

	cpumask_var_t		tracing_cpumask; /* only trace on set CPUs */

	/* one per_cpu trace_pipe can be opened by only one user */

	cpumask_var_t		pipe_cpumask;

	int			ref;

	int			trace_ref;

#ifdef CONFIG_FUNCTION_TRACER