Re: [PATCH 2/2] perf/x86: Disable precise sampling for PERF_SAMPLE_STACK_USER

[Peter Zijlstra]

On Tue, Sep 08, 2026 at 03:51:02PM +0800, Dapeng Mi wrote:
> PERF_SAMPLE_STACK_USER needs to return the user stack and user registers
> to user space when the PMI exits. Since the skid from the PEBS/IBS sample
> and PMI delivery, the PEBS/IBS register snapshot (especially IP/SP/BP)
> can diverge from the user stack at PMI return. That mismatch breaks DWARF
> unwinding.
> 
> Precise sampling provides no benefit in this case, so disable PEBS/IBS
> precise sampling and allow only PMI-based sampling when
> PERF_SAMPLE_STACK_USER is requested.
> 
> Reported-by: Gennady Kupava <gennady.kupava@xxxxxxxxx>
> Closes: https://lore.kernel.org/all/CAPu-DQqF0aF6=GS8Z6KKWeeX_V5LiXeKU_rJQZC+uGg8zuTPNw@xxxxxxxxxxxxxx/
> Cc: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> Fixes: c5ebcedb566e ("perf: Add ability to attach user stack dump to sample")
> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

This breaks long standing existing behaviour.