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: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Zheng Yejian 2023-08-18 10:26:45 +08:00 committed by Steven Rostedt (Google)
parent eecb91b9f9
commit c2489bb7e6
2 changed files with 50 additions and 7 deletions

View File

@ -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:

View File

@ -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