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Wed, 26 Apr 2017 12:39:58 +0000 Date: Wed, 26 Apr 2017 15:39:47 +0300 From: Yury Norov To: Peter Zijlstra Subject: Re: [PATCH 3/3] arm64/locking: qspinlocks and qrwlocks support Message-ID: <20170426123947.ogap6xgg7xc5wsd4@yury-N73SV> References: <1491860104-4103-1-git-send-email-ynorov@caviumnetworks.com> <1491860104-4103-4-git-send-email-ynorov@caviumnetworks.com> <20170413181212.y3ezah76qoztxhnn@hirez.programming.kicks-ass.net> <20170420182318.4ddtfiobxz6hgbo4@yury-N73SV> <20170420190530.GA6873@worktop> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20170420190530.GA6873@worktop> User-Agent: NeoMutt/20170113 (1.7.2) X-Originating-IP: [176.59.50.245] X-ClientProxiedBy: VI1P190CA0028.EURP190.PROD.OUTLOOK.COM (10.165.188.169) To DM2PR0701MB1280.namprd07.prod.outlook.com (10.161.225.18) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 7c2a5b1e-5ab3-4c08-b5dd-08d48ca159f2 X-Microsoft-Antispam: UriScan:; BCL:0; PCL:0; RULEID:(22001)(201703131423075)(201703031133081); 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And Jan did it > > on ThunderX, and Adam on QDF2400 without any problems. So even if I > > rework those functions, how could I check them for correctness? > > Running them doesn't prove them correct. Memory ordering bugs have been > in the kernel for many years without 'ever' triggering. This is stuff > you have to think about. > > > Anyway, regarding the queued_spin_unlock_wait(), is my understanding > > correct that you assume adding smp_mb() before entering the for(;;) > > cycle, and using ldaxr/strxr instead of atomic_read()? > > You'll have to ask Will, I always forget the arm64 details. So, below is what I have. For queued_spin_unlock_wait() the generated code is looking like this: ffff0000080983a0 : ffff0000080983a0: d5033bbf dmb ish ffff0000080983a4: b9400007 ldr w7, [x0] ffff0000080983a8: 350000c7 cbnz w7, ffff0000080983c0 ffff0000080983ac: 1400000e b ffff0000080983e4 ffff0000080983b0: d503203f yield ffff0000080983b4: d5033bbf dmb ish ffff0000080983b8: b9400007 ldr w7, [x0] ffff0000080983bc: 34000147 cbz w7, ffff0000080983e4 ffff0000080983c0: f2401cff tst x7, #0xff ffff0000080983c4: 54ffff60 b.eq ffff0000080983b0 ffff0000080983c8: 14000003 b ffff0000080983d4 ffff0000080983cc: d503201f nop ffff0000080983d0: d503203f yield ffff0000080983d4: d5033bbf dmb ish ffff0000080983d8: b9400007 ldr w7, [x0] ffff0000080983dc: f2401cff tst x7, #0xff ffff0000080983e0: 54ffff81 b.ne ffff0000080983d0 ffff0000080983e4: d50339bf dmb ishld ffff0000080983e8: d65f03c0 ret ffff0000080983ec: d503201f nop If I understand the documentation correctly, it's enough to check the lock properly. If not - please give me the clue. Will? Yury diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 22dbde97eefa..2d80161ee367 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -25,6 +25,8 @@ config ARM64 select ARCH_WANT_COMPAT_IPC_PARSE_VERSION select ARCH_WANT_FRAME_POINTERS select ARCH_HAS_UBSAN_SANITIZE_ALL + select ARCH_USE_QUEUED_SPINLOCKS + select ARCH_USE_QUEUED_RWLOCKS select ARM_AMBA select ARM_ARCH_TIMER select ARM_GIC diff --git a/arch/arm64/include/asm/qrwlock.h b/arch/arm64/include/asm/qrwlock.h new file mode 100644 index 000000000000..626f6ebfb52d --- /dev/null +++ b/arch/arm64/include/asm/qrwlock.h @@ -0,0 +1,7 @@ +#ifndef _ASM_ARM64_QRWLOCK_H +#define _ASM_ARM64_QRWLOCK_H + +#include +#include + +#endif /* _ASM_ARM64_QRWLOCK_H */ diff --git a/arch/arm64/include/asm/qspinlock.h b/arch/arm64/include/asm/qspinlock.h new file mode 100644 index 000000000000..09ef4f13f549 --- /dev/null +++ b/arch/arm64/include/asm/qspinlock.h @@ -0,0 +1,42 @@ +#ifndef _ASM_ARM64_QSPINLOCK_H +#define _ASM_ARM64_QSPINLOCK_H + +#include +#include + +extern void queued_spin_unlock_wait(struct qspinlock *lock); +#define queued_spin_unlock_wait queued_spin_unlock_wait + +#define queued_spin_unlock queued_spin_unlock +/** + * queued_spin_unlock - release a queued spinlock + * @lock : Pointer to queued spinlock structure + * + * A smp_store_release() on the least-significant byte. + */ +static __always_inline void queued_spin_unlock(struct qspinlock *lock) +{ + smp_store_release((u8 *)lock, 0); +} + +#define queued_spin_is_locked queued_spin_is_locked +/** + * queued_spin_is_locked - is the spinlock locked? + * @lock: Pointer to queued spinlock structure + * Return: 1 if it is locked, 0 otherwise + */ +static __always_inline int queued_spin_is_locked(struct qspinlock *lock) +{ + /* + * See queued_spin_unlock_wait(). + * + * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL + * isn't immediately observable. + */ + smp_mb(); + return atomic_read(&lock->val); +} + +#include + +#endif /* _ASM_ARM64_QSPINLOCK_H */ diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h index cae331d553f8..37713397e0c5 100644 --- a/arch/arm64/include/asm/spinlock.h +++ b/arch/arm64/include/asm/spinlock.h @@ -20,6 +20,10 @@ #include #include +#ifdef CONFIG_QUEUED_SPINLOCKS +#include +#else + /* * Spinlock implementation. * @@ -187,6 +191,12 @@ static inline int arch_spin_is_contended(arch_spinlock_t *lock) } #define arch_spin_is_contended arch_spin_is_contended +#endif /* CONFIG_QUEUED_SPINLOCKS */ + +#ifdef CONFIG_QUEUED_RWLOCKS +#include +#else + /* * Write lock implementation. * @@ -351,6 +361,8 @@ static inline int arch_read_trylock(arch_rwlock_t *rw) /* read_can_lock - would read_trylock() succeed? */ #define arch_read_can_lock(x) ((x)->lock < 0x80000000) +#endif /* CONFIG_QUEUED_RWLOCKS */ + #define arch_read_lock_flags(lock, flags) arch_read_lock(lock) #define arch_write_lock_flags(lock, flags) arch_write_lock(lock) diff --git a/arch/arm64/include/asm/spinlock_types.h b/arch/arm64/include/asm/spinlock_types.h index 55be59a35e3f..0f0f1561ab6a 100644 --- a/arch/arm64/include/asm/spinlock_types.h +++ b/arch/arm64/include/asm/spinlock_types.h @@ -16,9 +16,9 @@ #ifndef __ASM_SPINLOCK_TYPES_H #define __ASM_SPINLOCK_TYPES_H -#if !defined(__LINUX_SPINLOCK_TYPES_H) && !defined(__ASM_SPINLOCK_H) -# error "please don't include this file directly" -#endif +#ifdef CONFIG_QUEUED_SPINLOCKS +#include +#else #include @@ -36,10 +36,18 @@ typedef struct { #define __ARCH_SPIN_LOCK_UNLOCKED { 0 , 0 } +#endif /* CONFIG_QUEUED_SPINLOCKS */ + +#ifdef CONFIG_QUEUED_RWLOCKS +#include +#else + typedef struct { volatile unsigned int lock; } arch_rwlock_t; #define __ARCH_RW_LOCK_UNLOCKED { 0 } +#endif /* CONFIG_QUEUED_RWLOCKS */ + #endif diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 9d56467dc223..f48f6256e893 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -56,6 +56,7 @@ arm64-obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o \ arm64-obj-$(CONFIG_ARM64_RELOC_TEST) += arm64-reloc-test.o arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o +arm64-obj-$(CONFIG_QUEUED_SPINLOCKS) += qspinlock.o obj-y += $(arm64-obj-y) vdso/ probes/ obj-$(CONFIG_ARM64_ILP32) += vdso-ilp32/ diff --git a/arch/arm64/kernel/qspinlock.c b/arch/arm64/kernel/qspinlock.c new file mode 100644 index 000000000000..924f19953adb --- /dev/null +++ b/arch/arm64/kernel/qspinlock.c @@ -0,0 +1,34 @@ +#include +#include + +void queued_spin_unlock_wait(struct qspinlock *lock) +{ + u32 val; + + for (;;) { + smp_mb(); + val = atomic_read(&lock->val); + + if (!val) /* not locked, we're done */ + goto done; + + if (val & _Q_LOCKED_MASK) /* locked, go wait for unlock */ + break; + + /* not locked, but pending, wait until we observe the lock */ + cpu_relax(); + } + + for (;;) { + smp_mb(); + val = atomic_read(&lock->val); + if (!(val & _Q_LOCKED_MASK)) /* any unlock is good */ + break; + + cpu_relax(); + } + +done: + smp_acquire__after_ctrl_dep(); +} +EXPORT_SYMBOL(queued_spin_unlock_wait);