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Date: Tue, 22 Mar 2022 11:29:13 +0800
From: Guo Ren <guoren@...nel.org>
To: Stafford Horne <shorne@...il.com>
Cc: Palmer Dabbelt <palmer@...osinc.com>,
linux-riscv <linux-riscv@...ts.infradead.org>,
Peter Zijlstra <peterz@...radead.org>,
Jonas Bonn <jonas@...thpole.se>,
Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Arnd Bergmann <arnd@...db.de>, jszhang@...nel.org,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Openrisc <openrisc@...ts.librecores.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 3/5] openrisc: Move to ticket-spinlock
On Tue, Mar 22, 2022 at 7:23 AM Stafford Horne <shorne@...il.com> wrote:
>
> On Wed, Mar 16, 2022 at 04:25:58PM -0700, Palmer Dabbelt wrote:
> > From: Peter Zijlstra <peterz@...radead.org>
> >
> > We have no indications that openrisc meets the qspinlock requirements,
> > so move to ticket-spinlock as that is more likey to be correct.
> >
> > Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
> >
> > ---
> >
> > I have specifically not included Peter's SOB on this, as he sent his
> > original patch
> > <https://lore.kernel.org/lkml/YHbBBuVFNnI4kjj3@hirez.programming.kicks-ass.net/>
> > without one.
> > ---
> > arch/openrisc/Kconfig | 1 -
> > arch/openrisc/include/asm/Kbuild | 5 ++---
> > arch/openrisc/include/asm/spinlock.h | 3 +--
> > arch/openrisc/include/asm/spinlock_types.h | 2 +-
> > 4 files changed, 4 insertions(+), 7 deletions(-)
>
> Hello,
>
> This series breaks SMP support on OpenRISC. I haven't traced it down yet, it
> seems trivial but I have a few places to check.
>
> I replied to this on a kbuild warning thread, but also going to reply here with
> more information.
>
> https://lore.kernel.org/lkml/YjeY7CfaFKjr8IUc@antec/#R
>
> So far this is what I see:
>
> * ticket_lock is stuck trying to lock console_sem
> * it is stuck on atomic_cond_read_acquire
> reading lock value: returns 0 (*lock is 0x10000)
> ticket value: is 1
> * possible issues:
> - OpenRISC is big endian, that seems to impact ticket_unlock, it looks
All csky & riscv are little-endian, it seems the series has a bug with
big-endian. Is that all right for qemu? (If qemu was all right, but
real hardware failed.)
> like we are failing on the first call to ticket_lock though
>
> Backtrace:
> (gdb) target remote :10001
> Remote debugging using :10001
> ticket_lock (lock=0xc049e078 <console_sem>) at include/asm-generic/ticket-lock.h:39
> 39 atomic_cond_read_acquire(lock, ticket == (u16)VAL);
> (gdb) bt
> #0 ticket_lock (lock=0xc049e078 <console_sem>) at include/asm-generic/ticket-lock.h:39
> #1 do_raw_spin_lock (lock=0xc049e078 <console_sem>) at include/linux/spinlock.h:185
> #2 __raw_spin_lock_irqsave (lock=0xc049e078 <console_sem>) at include/linux/spinlock_api_smp.h:111
> #3 _raw_spin_lock_irqsave (lock=0xc049e078 <console_sem>) at kernel/locking/spinlock.c:162
> Backtrace stopped: Cannot access memory at address 0xc0491ee8
>
> Code:
>
> 31 static __always_inline void ticket_lock(arch_spinlock_t *lock)
> 32 {
> 33 u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */
> 34 u16 ticket = val >> 16;
> 35
> 36 if (ticket == (u16)val)
> 37 return;
> 38
> 39 atomic_cond_read_acquire(lock, ticket == (u16)VAL); <--- stuck here
> 40 }
>
> Assembly:
>
> c04232ac <_raw_spin_lock_irqsave>:
> c04232ac: 9c 21 ff f0 l.addi r1,r1,-16
> c04232b0: d4 01 10 08 l.sw 8(r1),r2
> c04232b4: 9c 41 00 10 l.addi r2,r1,16
> c04232b8: d4 01 80 00 l.sw 0(r1),r16
> c04232bc: d4 01 90 04 l.sw 4(r1),r18
> c04232c0: d4 01 48 0c l.sw 12(r1),r9
> c04232c4: 07 ef 8b 35 l.jal c0005f98 <arch_local_save_flags>
> c04232c8: e2 03 18 04 l.or r16,r3,r3
> c04232cc: 18 60 00 00 l.movhi r3,0x0
> c04232d0: 07 ef 8b 3c l.jal c0005fc0 <arch_local_irq_restore>
> c04232d4: e2 4b 58 04 l.or r18,r11,r11
> c04232d8: 1a 60 00 01 l.movhi r19,0x1
> atomic_fetch_add:
> c04232dc: 6e 30 00 00 l.lwa r17,0(r16)
> c04232e0: e2 31 98 00 l.add r17,r17,r19
> c04232e4: cc 10 88 00 l.swa 0(r16),r17
> c04232e8: 0f ff ff fd l.bnf c04232dc <_raw_spin_lock_irqsave+0x30>
> c04232ec: 15 00 00 00 l.nop 0x0
> u16 ticket = val >> 16;
> c04232f0: ba 71 00 50 l.srli r19,r17,0x10
> c04232f4: a6 31 ff ff l.andi r17,r17,0xffff
> c04232f8: e4 13 88 00 l.sfeq r19,r17
> c04232fc: 10 00 00 0e l.bf c0423334 <_raw_spin_lock_irqsave+0x88>
> c0423300: e1 72 90 04 l.or r11,r18,r18
> if (ticket == (u16)val):
> c0423304: 86 30 00 00 l.lwz r17,0(r16)
> c0423308: a6 31 ff ff l.andi r17,r17,0xffff
> c042330c: e4 11 98 00 l.sfeq r17,r19
> c0423310: 10 00 00 07 l.bf c042332c <_raw_spin_lock_irqsave+0x80>
> c0423314: 15 00 00 00 l.nop 0x0
> atomic_cond_read_acquire:
> c0423318: 86 30 00 00 l.lwz r17,0(r16)
> c042331c: a6 31 ff ff l.andi r17,r17,0xffff
> c0423320: e4 33 88 00 l.sfne r19,r17
> c0423324: 13 ff ff fd l.bf c0423318 <_raw_spin_lock_irqsave+0x6c>
> c0423328: 15 00 00 00 l.nop 0x0
> c042332c: 22 00 00 00 l.msync
> c0423330: e1 72 90 04 l.or r11,r18,r18
> c0423334: 86 01 00 00 l.lwz r16,0(r1)
> c0423338: 86 41 00 04 l.lwz r18,4(r1)
> c042333c: 84 41 00 08 l.lwz r2,8(r1)
> c0423340: 85 21 00 0c l.lwz r9,12(r1)
> c0423344: 44 00 48 00 l.jr r9
> c0423348: 9c 21 00 10 l.addi r1,r1,16
>
>
> -Stafford
>
> > diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
> > index f724b3f1aeed..f5fa226362f6 100644
> > --- a/arch/openrisc/Kconfig
> > +++ b/arch/openrisc/Kconfig
> > @@ -30,7 +30,6 @@ config OPENRISC
> > select HAVE_DEBUG_STACKOVERFLOW
> > select OR1K_PIC
> > select CPU_NO_EFFICIENT_FFS if !OPENRISC_HAVE_INST_FF1
> > - select ARCH_USE_QUEUED_SPINLOCKS
> > select ARCH_USE_QUEUED_RWLOCKS
> > select OMPIC if SMP
> > select ARCH_WANT_FRAME_POINTERS
> > diff --git a/arch/openrisc/include/asm/Kbuild b/arch/openrisc/include/asm/Kbuild
> > index ca5987e11053..cb260e7d73db 100644
> > --- a/arch/openrisc/include/asm/Kbuild
> > +++ b/arch/openrisc/include/asm/Kbuild
> > @@ -1,9 +1,8 @@
> > # SPDX-License-Identifier: GPL-2.0
> > generic-y += extable.h
> > generic-y += kvm_para.h
> > -generic-y += mcs_spinlock.h
> > -generic-y += qspinlock_types.h
> > -generic-y += qspinlock.h
> > +generic-y += ticket-lock.h
> > +generic-y += ticket-lock-types.h
> > generic-y += qrwlock_types.h
> > generic-y += qrwlock.h
> > generic-y += user.h
> > diff --git a/arch/openrisc/include/asm/spinlock.h b/arch/openrisc/include/asm/spinlock.h
> > index 264944a71535..40e4c9fdc349 100644
> > --- a/arch/openrisc/include/asm/spinlock.h
> > +++ b/arch/openrisc/include/asm/spinlock.h
> > @@ -15,8 +15,7 @@
> > #ifndef __ASM_OPENRISC_SPINLOCK_H
> > #define __ASM_OPENRISC_SPINLOCK_H
> >
> > -#include <asm/qspinlock.h>
> > -
> > +#include <asm/ticket-lock.h>
> > #include <asm/qrwlock.h>
> >
> > #define arch_spin_relax(lock) cpu_relax()
> > diff --git a/arch/openrisc/include/asm/spinlock_types.h b/arch/openrisc/include/asm/spinlock_types.h
> > index 7c6fb1208c88..58ea31fa65ce 100644
> > --- a/arch/openrisc/include/asm/spinlock_types.h
> > +++ b/arch/openrisc/include/asm/spinlock_types.h
> > @@ -1,7 +1,7 @@
> > #ifndef _ASM_OPENRISC_SPINLOCK_TYPES_H
> > #define _ASM_OPENRISC_SPINLOCK_TYPES_H
> >
> > -#include <asm/qspinlock_types.h>
> > +#include <asm/ticket-lock-types.h>
> > #include <asm/qrwlock_types.h>
> >
> > #endif /* _ASM_OPENRISC_SPINLOCK_TYPES_H */
> > --
> > 2.34.1
> >
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
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