Re: [PATCH v2] perf/core: Drop __weak attribute from arch_perf_update_userpage() prototype

[Peter Zijlstra]

On Fri, Jun 16, 2023 at 12:48:31PM +0100, Marc Zyngier wrote:
> Reiji reports that the arm64 implementation of arch_perf_update_userpage()
> is now ignored and replaced by the dummy stub in core code.
> This seems to happen since the PMUv3 driver was moved to driver/perf.
> 
> As it turns out, dropping the __weak attribute from the *prototype*
> of the function solves the problem. You're right, this doesn't seem
> to make much sense. And yet... It appears that both symbols get
> flagged as weak, and that the first one to appear in the link order
> wins:
> 
> $ nm drivers/perf/arm_pmuv3.o|grep arch_perf_update_userpage
> 0000000000001db0 W arch_perf_update_userpage
> 
> Dropping the attribute from the prototype restores the expected
> behaviour, and arm64 is able to enjoy arch_perf_update_userpage()
> again.
> 
> Fixes: 7755cec63ade ("arm64: perf: Move PMUv3 driver to drivers/perf")
> Fixes: f1ec3a517b43 ("kernel/events: Add a missing prototype for arch_perf_update_userpage()")
> Reported-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> Tested-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>

Thanks! in perf/urgent it goes