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Message-ID: <YjjuOZMzQlnqfLDJ@antec>
Date: Tue, 22 Mar 2022 06:29:29 +0900
From: Stafford Horne <shorne@...il.com>
To: Palmer Dabbelt <palmer@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, peterz@...radead.org,
jonas@...thpole.se, stefan.kristiansson@...nalahti.fi,
mingo@...hat.com, Will Deacon <will@...nel.org>,
longman@...hat.com, boqun.feng@...il.com,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
Arnd Bergmann <arnd@...db.de>, jszhang@...nel.org,
wangkefeng.wang@...wei.com, openrisc@...ts.librecores.org,
linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 3/5] openrisc: Move to ticket-spinlock
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
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
>
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