linux-kernel - Re: [PATCH v2] perf/core: Drop __weak attribute from arch_perf_update

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Date:   Fri, 16 Jun 2023 12:57:02 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Reiji Watanabe <reijiw@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v2] perf/core: Drop __weak attribute from
 arch_perf_update_userpage() prototype

On 2023-06-16 12:48, 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@...gle.com>
> Tested-by: Reiji Watanabe <reijiw@...gle.com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will@...nel.org>

And of course I forgot to pass --notes to git-send-email...

     v2: Added fixes tags, both for the commit that introduce the 
breakage
         on arm64, and for the commit introducing the offending 
prototype.
         I did not Cc stable on purpose, as nothing appears to be broken
         in other architectures.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...