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

commit 3d07fa1dd1 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: c2489bb7e6 ("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>
This commit is contained in:
Brian Foster 2023-08-31 08:55:00 -04:00 committed by Greg Kroah-Hartman
parent e43a7ae58d
commit 1dd387668d
1 changed files with 2 additions and 2 deletions
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4
kernel/trace/trace.c
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@ -9395,7 +9395,7 @@ 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;
@ -10267,7 +10267,7 @@ __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 */