Commit 3d07fa1d authored by Brian Foster's avatar Brian Foster Committed by Steven Rostedt (Google)
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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: c2489bb7 ("tracing: Introduce pipe_cpumask to avoid race on trace_pipes")
Reviewed-by: default avatarZheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 2a30dbcb

kernel/trace/trace.c

+2 −2
Original line number Diff line number Diff line
@@ -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 */