From: Brian Foster bfoster@redhat.com

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@r...

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 --- kernel/trace/trace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 23579fba1a57..35783a7baf15 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9474,7 +9474,7 @@ 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)) + if (!zalloc_cpumask_var(&tr->pipe_cpumask, GFP_KERNEL)) goto out_free_tr;

tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS; @@ -10419,7 +10419,7 @@ __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)) + if (!zalloc_cpumask_var(&global_trace.pipe_cpumask, GFP_KERNEL)) goto out_free_savedcmd;

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