linux-kernel - Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C interrupt entry

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Date:   Thu, 11 Mar 2021 13:38:00 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 36/43] powerpc/32: Set current->thread.regs in C
 interrupt entry



Le 11/03/2021 à 11:38, Christophe Leroy a écrit :
> 
> 
> Le 10/03/2021 à 02:33, Nicholas Piggin a écrit :
>> Excerpts from Christophe Leroy's message of March 9, 2021 10:10 pm:
>>> No need to do that is assembly, do it in C.
>>
>> Hmm. No issues with the patch as such, but why does ppc32 need this but
>> not 64? AFAIKS 64 sets this when a thread is created.
> 
> Looks like ppc64 was doing the same in function save_remaining_regs() in arch/ppc64/kernel/head.S 
> until commit https://github.com/mpe/linux-fullhistory/commit/e5bb080d
> 
> But I can't find what happend to it in that commit.
> 
> Where is it done now ? Maybe that's also already done for ppc32.
> 

I digged a bit more and found a later bug fix which adds that setting of current->thread.regs at 
task creation: https://github.com/mpe/linux-fullhistory/commit/3eac1897

That was in the ppc64 tree only at that time, and was merged into the common powerpc tree via commit 
https://github.com/mpe/linux-fullhistory/commit/06d67d54

So we have it for both ppc32 and ppc64 and ppc32 doesn't need to do it at exception entry anymore. 
I'll remove it.

Thanks
Christophe