Subject: Re: [PATCH 20/28] coresight: tmc-etr: Do not call smp_processor_id() from preemptible

From: Greg KH <[email-masked]>
Date: Thu, 20 Jun 2019 08:02:50 +0200

On Wed, Jun 19, 2019 at 01:53:10PM -0600, Mathieu Poirier wrote:
> From: Suzuki K Poulose <[email-masked]>
> 
> During a perf session we try to allocate buffers on the "node" associated
> with the CPU the event is bound to. If it's not bound to a CPU, we use
> the current CPU node, using smp_processor_id(). However this is unsafe
> in a pre-emptible context and could generate the splats as below :
> 
>  BUG: using smp_processor_id() in preemptible [00000000] code: perf/1743
>  caller is alloc_etr_buf.isra.6+0x80/0xa0
>  CPU: 1 PID: 1743 Comm: perf Not tainted 5.1.0-rc6-147786-g116841e #344
>  Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Feb  1 2019
>   Call trace:
>    dump_backtrace+0x0/0x150
>    show_stack+0x14/0x20
>    dump_stack+0x9c/0xc4
>    debug_smp_processor_id+0x10c/0x110
>    alloc_etr_buf.isra.6+0x80/0xa0
>    tmc_alloc_etr_buffer+0x12c/0x1f0
>    etm_setup_aux+0x1c4/0x230
>    rb_alloc_aux+0x1b8/0x2b8
>    perf_mmap+0x35c/0x478
>    mmap_region+0x34c/0x4f0
>    do_mmap+0x2d8/0x418
>    vm_mmap_pgoff+0xd0/0xf8
>    ksys_mmap_pgoff+0x88/0xf8
>    __arm64_sys_mmap+0x28/0x38
>    el0_svc_handler+0xd8/0x138
>    el0_svc+0x8/0xc
> 
> Use NUMA_NO_NODE hint instead of using the current node for events
> not bound to CPUs.
> 
> Fixes: 855ab61c16bf70b646 ("coresight: tmc-etr: Refactor function tmc_etr_setup_perf_buf()")
> Cc: Mathieu Poirier <[email-masked]>
> Signed-off-by: Suzuki K Poulose <[email-masked]>
> Signed-off-by: Mathieu Poirier <[email-masked]>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)

Why isn't this being submitted for 5.2-final?  Why wait until 5.3 to fix
this?

thanks,

greg k-h

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