Messages in this thread Patch in this message | | | From | Brian Foster <> | Subject | [PATCH] tracing: zero the pipe cpumask on alloc to avoid spurious -EBUSY | Date | Thu, 31 Aug 2023 08:55:00 -0400 |
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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.
Fixes: c2489bb7e6be ("tracing: Introduce pipe_cpumask to avoid race on trace_pipes") Signed-off-by: Brian Foster <bfoster@redhat.com> ---
Hi,
I ran into this problem just recently on one of my test VMs immediately after updating to a v6.5 base. A revert of the aforementioned commit addressed the problem. I'm not terribly familiar with the tracing code, but on further inspection I noticed the cpumask doesn't appear to be initialized anywhere. I suppose this could alternatively do a cpumask_clear() or whatever after allocation, but either way this addresses the problem for me.
Please CC on replies as I'm not subscribed to the list. Thanks.
Brian
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 8e64aaad5361..2656ca3b9b39 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -9486,7 +9486,7 @@ 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; @@ -10431,7 +10431,7 @@ __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 */ -- 2.41.0
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