diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2022-05-26 20:50:30 +0300 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2022-05-26 20:50:30 +0300 |
commit | 16477cdfefdb494235a675cc80563d736991d833 (patch) | |
tree | ccb761eb4574446f8b3d400037add1801f550837 /include | |
parent | ecf0aa5317b0ad6bb015128a5b763c954fd58708 (diff) | |
parent | b2441b3bdce6c02cb96278d98c620d7ba1d41b7b (diff) | |
download | linux-16477cdfefdb494235a675cc80563d736991d833.tar.xz |
Merge tag 'asm-generic-5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic
Pull asm-generic updates from Arnd Bergmann:
"The asm-generic tree contains three separate changes for linux-5.19:
- The h8300 architecture is retired after it has been effectively
unmaintained for a number of years. This is the last architecture
we supported that has no MMU implementation, but there are still a
few architectures (arm, m68k, riscv, sh and xtensa) that support
CPUs with and without an MMU.
- A series to add a generic ticket spinlock that can be shared by
most architectures with a working cmpxchg or ll/sc type atomic,
including the conversion of riscv, csky and openrisc. This series
is also a prerequisite for the loongarch64 architecture port that
will come as a separate pull request.
- A cleanup of some exported uapi header files to ensure they can be
included from user space without relying on other kernel headers"
* tag 'asm-generic-5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
h8300: remove stale bindings and symlink
sparc: add asm/stat.h to UAPI compile-test coverage
powerpc: add asm/stat.h to UAPI compile-test coverage
mips: add asm/stat.h to UAPI compile-test coverage
riscv: add linux/bpf_perf_event.h to UAPI compile-test coverage
kbuild: prevent exported headers from including <stdlib.h>, <stdbool.h>
agpgart.h: do not include <stdlib.h> from exported header
csky: Move to generic ticket-spinlock
RISC-V: Move to queued RW locks
RISC-V: Move to generic spinlocks
openrisc: Move to ticket-spinlock
asm-generic: qrwlock: Document the spinlock fairness requirements
asm-generic: qspinlock: Indicate the use of mixed-size atomics
asm-generic: ticket-lock: New generic ticket-based spinlock
remove the h8300 architecture
Diffstat (limited to 'include')
-rw-r--r-- | include/asm-generic/qrwlock.h | 4 | ||||
-rw-r--r-- | include/asm-generic/qspinlock.h | 29 | ||||
-rw-r--r-- | include/asm-generic/spinlock.h | 94 | ||||
-rw-r--r-- | include/asm-generic/spinlock_types.h | 17 | ||||
-rw-r--r-- | include/uapi/linux/agpgart.h | 9 |
5 files changed, 141 insertions, 12 deletions
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h index d4cd4cc4389c..75b8f4601b28 100644 --- a/include/asm-generic/qrwlock.h +++ b/include/asm-generic/qrwlock.h @@ -2,6 +2,10 @@ /* * Queue read/write lock * + * These use generic atomic and locking routines, but depend on a fair spinlock + * implementation in order to be fair themselves. The implementation in + * asm-generic/spinlock.h meets these requirements. + * * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. * * Authors: Waiman Long <waiman.long@hp.com> diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h index d74b13825501..995513fa2690 100644 --- a/include/asm-generic/qspinlock.h +++ b/include/asm-generic/qspinlock.h @@ -2,6 +2,35 @@ /* * Queued spinlock * + * A 'generic' spinlock implementation that is based on MCS locks. For an + * architecture that's looking for a 'generic' spinlock, please first consider + * ticket-lock.h and only come looking here when you've considered all the + * constraints below and can show your hardware does actually perform better + * with qspinlock. + * + * qspinlock relies on atomic_*_release()/atomic_*_acquire() to be RCsc (or no + * weaker than RCtso if you're power), where regular code only expects atomic_t + * to be RCpc. + * + * qspinlock relies on a far greater (compared to asm-generic/spinlock.h) set + * of atomic operations to behave well together, please audit them carefully to + * ensure they all have forward progress. Many atomic operations may default to + * cmpxchg() loops which will not have good forward progress properties on + * LL/SC architectures. + * + * One notable example is atomic_fetch_or_acquire(), which x86 cannot (cheaply) + * do. Carefully read the patches that introduced + * queued_fetch_set_pending_acquire(). + * + * qspinlock also heavily relies on mixed size atomic operations, in specific + * it requires architectures to have xchg16; something which many LL/SC + * architectures need to implement as a 32bit and+or in order to satisfy the + * forward progress guarantees mentioned above. + * + * Further reading on mixed size atomics that might be relevant: + * + * http://www.cl.cam.ac.uk/~pes20/popl17/mixed-size.pdf + * * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP * diff --git a/include/asm-generic/spinlock.h b/include/asm-generic/spinlock.h index adaf6acab172..fdfebcb050f4 100644 --- a/include/asm-generic/spinlock.h +++ b/include/asm-generic/spinlock.h @@ -1,12 +1,92 @@ /* SPDX-License-Identifier: GPL-2.0 */ -#ifndef __ASM_GENERIC_SPINLOCK_H -#define __ASM_GENERIC_SPINLOCK_H + /* - * You need to implement asm/spinlock.h for SMP support. The generic - * version does not handle SMP. + * 'Generic' ticket-lock implementation. + * + * It relies on atomic_fetch_add() having well defined forward progress + * guarantees under contention. If your architecture cannot provide this, stick + * to a test-and-set lock. + * + * It also relies on atomic_fetch_add() being safe vs smp_store_release() on a + * sub-word of the value. This is generally true for anything LL/SC although + * you'd be hard pressed to find anything useful in architecture specifications + * about this. If your architecture cannot do this you might be better off with + * a test-and-set. + * + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence + * uses atomic_fetch_add() which is RCsc to create an RCsc hot path, along with + * a full fence after the spin to upgrade the otherwise-RCpc + * atomic_cond_read_acquire(). + * + * The implementation uses smp_cond_load_acquire() to spin, so if the + * architecture has WFE like instructions to sleep instead of poll for word + * modifications be sure to implement that (see ARM64 for example). + * */ -#ifdef CONFIG_SMP -#error need an architecture specific asm/spinlock.h -#endif + +#ifndef __ASM_GENERIC_SPINLOCK_H +#define __ASM_GENERIC_SPINLOCK_H + +#include <linux/atomic.h> +#include <asm-generic/spinlock_types.h> + +static __always_inline void arch_spin_lock(arch_spinlock_t *lock) +{ + u32 val = atomic_fetch_add(1<<16, lock); + u16 ticket = val >> 16; + + if (ticket == (u16)val) + return; + + /* + * atomic_cond_read_acquire() is RCpc, but rather than defining a + * custom cond_read_rcsc() here we just emit a full fence. We only + * need the prior reads before subsequent writes ordering from + * smb_mb(), but as atomic_cond_read_acquire() just emits reads and we + * have no outstanding writes due to the atomic_fetch_add() the extra + * orderings are free. + */ + atomic_cond_read_acquire(lock, ticket == (u16)VAL); + smp_mb(); +} + +static __always_inline bool arch_spin_trylock(arch_spinlock_t *lock) +{ + u32 old = atomic_read(lock); + + if ((old >> 16) != (old & 0xffff)) + return false; + + return atomic_try_cmpxchg(lock, &old, old + (1<<16)); /* SC, for RCsc */ +} + +static __always_inline void arch_spin_unlock(arch_spinlock_t *lock) +{ + u16 *ptr = (u16 *)lock + IS_ENABLED(CONFIG_CPU_BIG_ENDIAN); + u32 val = atomic_read(lock); + + smp_store_release(ptr, (u16)val + 1); +} + +static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock) +{ + u32 val = atomic_read(lock); + + return ((val >> 16) != (val & 0xffff)); +} + +static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock) +{ + u32 val = atomic_read(lock); + + return (s16)((val >> 16) - (val & 0xffff)) > 1; +} + +static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) +{ + return !arch_spin_is_locked(&lock); +} + +#include <asm/qrwlock.h> #endif /* __ASM_GENERIC_SPINLOCK_H */ diff --git a/include/asm-generic/spinlock_types.h b/include/asm-generic/spinlock_types.h new file mode 100644 index 000000000000..8962bb730945 --- /dev/null +++ b/include/asm-generic/spinlock_types.h @@ -0,0 +1,17 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef __ASM_GENERIC_SPINLOCK_TYPES_H +#define __ASM_GENERIC_SPINLOCK_TYPES_H + +#include <linux/types.h> +typedef atomic_t arch_spinlock_t; + +/* + * qrwlock_types depends on arch_spinlock_t, so we must typedef that before the + * include. + */ +#include <asm/qrwlock_types.h> + +#define __ARCH_SPIN_LOCK_UNLOCKED ATOMIC_INIT(0) + +#endif /* __ASM_GENERIC_SPINLOCK_TYPES_H */ diff --git a/include/uapi/linux/agpgart.h b/include/uapi/linux/agpgart.h index f5251045181a..9cc3448c0b5b 100644 --- a/include/uapi/linux/agpgart.h +++ b/include/uapi/linux/agpgart.h @@ -52,7 +52,6 @@ #ifndef __KERNEL__ #include <linux/types.h> -#include <stdlib.h> struct agp_version { __u16 major; @@ -64,10 +63,10 @@ typedef struct _agp_info { __u32 bridge_id; /* bridge vendor/device */ __u32 agp_mode; /* mode info of bridge */ unsigned long aper_base;/* base of aperture */ - size_t aper_size; /* size of aperture */ - size_t pg_total; /* max pages (swap + system) */ - size_t pg_system; /* max pages (system) */ - size_t pg_used; /* current pages used */ + __kernel_size_t aper_size; /* size of aperture */ + __kernel_size_t pg_total; /* max pages (swap + system) */ + __kernel_size_t pg_system; /* max pages (system) */ + __kernel_size_t pg_used; /* current pages used */ } agp_info; typedef struct _agp_setup { |