linux-kernel - Re: [PATCH 07/14] powerpc: Add support for restartable sequences

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Date:   Fri, 18 May 2018 14:17:17 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 07/14] powerpc: Add support for restartable sequences

----- On May 17, 2018, at 7:50 PM, Boqun Feng boqun.feng@...il.com wrote:
[...]
>> > I think you're right. So we have to introduce callsite to rseq_syscall()
>> > in syscall path, something like:
>> > 
>> > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
>> > index 51695608c68b..a25734a96640 100644
>> > --- a/arch/powerpc/kernel/entry_64.S
>> > +++ b/arch/powerpc/kernel/entry_64.S
>> > @@ -222,6 +222,9 @@ system_call_exit:
>> > 	mtmsrd	r11,1
>> > #endif /* CONFIG_PPC_BOOK3E */
>> > 
>> > +	addi    r3,r1,STACK_FRAME_OVERHEAD
>> > +	bl	rseq_syscall
>> > +
>> > 	ld	r9,TI_FLAGS(r12)
>> > 	li	r11,-MAX_ERRNO
>> > 	andi.
>> > 		r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
>> > 

By the way, I think this is not the right spot to call rseq_syscall, because
interrupts are disabled. I think we should move this hunk right after system_call_exit.

Would you like to implement and test an updated patch adding those calls for ppc 32 and 64 ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com