[PATCH 5.10 310/406] tracing: Zero the pipe cpumask on alloc to avoid spurious -EBUSY

Greg Kroah-Hartman
2023-09-17T19:39:39Z

From: Brian Foster <bfoster@redhat.com>

commit 3d07fa1dd19035eb0b13ae6697efd5caa9033e74 upstream.

The pipe cpumask used to serialize opens between the main and percpu
trace pipes is not zeroed or initialized. This can result in
spurious -EBUSY returns if underlying memory is not fully zeroed.
This has been observed by immediate failure to read the main
trace_pipe file on an otherwise newly booted and idle system:

# cat /sys/kernel/debug/tracing/trace_pipe
cat: /sys/kernel/debug/tracing/trace_pipe: Device or resource busy

Zero the allocation of pipe_cpumask to avoid the problem.

Link: https://lore.kernel.org/linux-trace-kernel/20230831125500.986862-1-bfoster@redhat.com

Cc: stable@vger.kernel.org
Fixes: c2489bb7e6be ("tracing: Introduce pipe_cpumask to avoid race on trace_pipes")
Reviewed-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8890,7 +8890,7 @@ static struct trace_array *trace_array_c
if (!alloc_cpumask_var(&tr->tracing_cpumask, GFP_KERNEL))
goto out_free_tr;

- if (!alloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL))
goto out_free_tr;

tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS;
@@ -9736,7 +9736,7 @@ __init static int tracer_alloc_buffers(v
if (trace_create_savedcmd() < 0)
goto out_free_temp_buffer;

- if (!alloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL))
+ if (!zalloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL))
goto out_free_savedcmd;

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