Messages in this thread | | | Date | Thu, 31 Aug 2023 21:51:18 +0800 | Subject | Re: [PATCH] tracing: zero the pipe cpumask on alloc to avoid spurious -EBUSY | From | Zheng Yejian <> |
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On 2023/8/31 20:55, Brian Foster wrote: > 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.
Yes, pipe_cpumask must be initialized.
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Thanks, Zheng Yejian
> > 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 */
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