tracing: Zero the pipe cpumask on alloc to avoid spurious -EBUSY

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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 23579fba1a57e8ca964964c93b6a34fbec9e01d8..35783a7baf151cf7f3c7eb65cbf228bba433fe97 100644 (file)
--- 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 */