Expose a new system call allowing threads to register userspace memory areas where to store the current CPU number. Scheduler migration sets the TIF_NOTIFY_RESUME flag on the current thread. Upon return to user-space, a notify-resume handler updates the current CPU value within that user-space memory area.
This getcpu cache is an alternative to the sched_getcpu() vdso which has a few benefits: - A memory read is faster that an "lsl" instruction (x86), - A memory read is faster that performing a function call (x86), - A memory read is of course faster than a system call, - This cached value can be read from within an inline assembly, which makes it a useful building block for restartable sequences. - The getcpu cache approach is portable (e.g. ARM 32), which is not the case for the segment-based x86 vdso. This approach is inspired by Paul Turner and Andrew Hunter's work on percpu atomics, which lets the kernel handle restart of critical sections: Ref.: * https://lkml.org/lkml/2015/10/27/1095 * https://lkml.org/lkml/2015/6/24/665 * https://lwn.net/Articles/650333/ * http://www.linuxplumbersconf.org/2013/ocw/system/presentations/1695/original/LPC%20-%20PerCpu%20Atomics.pdf Benchmarking various approaches for reading the current CPU number on a x86-64 Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz: - Baseline (empty loop): 1.0 ns - Read CPU from thread-local ABI: 1.0 ns - "lsl" inline assembly: 11.2 ns - glibc 2.19-0ubuntu6.6 getcpu: 14.3 ns - getcpu system call: 51.0 ns The system call can be extended by registering a larger structure in the future. Man page associated: THREAD_LOCAL_ABI(2) Linux Programmer's Manual THREAD_LOCAL_ABI(2) NAME thread_local_abi - Interface between user-space threads and the kernel SYNOPSIS #include <linux/thread_local_abi.h> ssize_t thread_local_abi(struct thread_local_abi * tlap, size_t len, int flags); DESCRIPTION The thread_local_abi() helps speeding up some frequent operations such as reading the current CPU number by ensuring that the memory locations registered by user-space threads are always updated with the current information. The tlap argument is a pointer to a struct thread_local_abi. The len argument is the size of the struct thread_local_abi. If len is greater than 0, it means the tlap should be registered for the current thread. A len of 0 means that the tlap should be unregistered from the current thread. The flags argument is currently unused and must be specified as 0. Typically, a library or application will put struct thread_local_abi in a thread-local storage variable, or other memory areas belonging to each thread. Each thread is responsible for registering its own thread-local ABI. It is possible to register many thread-local ABI for a given thread, for instance from different libraries. RETURN VALUE When thread_local_abi is invoked with len greater than 0 (registra‐ tion), a return value greater or equal to 0 indicates success. The value returned is the minimum between the len argument and the struct thread_local_abi length supported by the kernel. This should be used to check whether the kernel supports the fields required by user-space. On error, -1 is returned, and errno is set appropriately. When thread_local_abi is invoked with a 0 len argument (unregistra‐ tion), a return value of 0 indicates success. On error, -1 is returned, and errno is set appropriately. ERRORS EINVAL tlap is invalid or flags is non-zero. ENOSYS The thread_local_abi() system call is not implemented by this kernel. ENOENT len is 0 (unregistration) and tlap cannot be found for this thread. EBUSY len is greater than 0 (registration) and tlap is already regis‐ tered for this thread. ENOMEM len is greater than 0 (registration) and we have run out of mem‐ ory. EFAULT len is greater than 0 (registration) and the memory location specified by tlap is a bad address. VERSIONS The thread_local_abi() system call was added in Linux 4.N (TODO). CONFORMING TO thread_local_abi() is Linux-specific. Linux 2015-12-22 THREAD_LOCAL_ABI(2) Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> CC: Thomas Gleixner <t...@linutronix.de> CC: Paul Turner <p...@google.com> CC: Andrew Hunter <a...@google.com> CC: Peter Zijlstra <pet...@infradead.org> CC: Andy Lutomirski <l...@amacapital.net> CC: Andi Kleen <a...@firstfloor.org> CC: Dave Watson <davejwat...@fb.com> CC: Chris Lameter <c...@linux.com> CC: Ingo Molnar <mi...@redhat.com> CC: Ben Maurer <bmau...@fb.com> CC: Steven Rostedt <rost...@goodmis.org> CC: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> CC: Josh Triplett <j...@joshtriplett.org> CC: Linus Torvalds <torva...@linux-foundation.org> CC: Andrew Morton <a...@linux-foundation.org> CC: Russell King <li...@arm.linux.org.uk> CC: Catalin Marinas <catalin.mari...@arm.com> CC: Will Deacon <will.dea...@arm.com> CC: Michael Kerrisk <mtk.manpa...@gmail.com> CC: linux-...@vger.kernel.org --- Changes since v1: * Allow multiple libraries to register their per-thread memory area. * Split system call wire up into separate patches. * Added man page to changelog. * This patchset applies on top of Linux 4.3. --- fs/exec.c | 1 + include/linux/init_task.h | 8 ++ include/linux/sched.h | 40 ++++++++ include/uapi/linux/Kbuild | 1 + include/uapi/linux/thread_local_abi.h | 37 ++++++++ init/Kconfig | 9 ++ kernel/Makefile | 1 + kernel/fork.c | 7 ++ kernel/sched/core.c | 3 + kernel/sched/sched.h | 2 + kernel/sys_ni.c | 3 + kernel/thread_local_abi.c | 174 ++++++++++++++++++++++++++++++++++ 12 files changed, 286 insertions(+) create mode 100644 include/uapi/linux/thread_local_abi.h create mode 100644 kernel/thread_local_abi.c diff --git a/fs/exec.c b/fs/exec.c index b06623a..88490cc 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1594,6 +1594,7 @@ static int do_execveat_common(int fd, struct filename *filename, /* execve succeeded */ current->fs->in_exec = 0; current->in_execve = 0; + thread_local_abi_execve(current); acct_update_integrals(current); task_numa_free(current); free_bprm(bprm); diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 1c1ff7e..69dd780 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -183,6 +183,13 @@ extern struct task_group root_task_group; # define INIT_KASAN(tsk) #endif +#ifdef CONFIG_THREAD_LOCAL_ABI +# define INIT_THREAD_LOCAL_ABI(tsk) \ + .thread_local_abi_head = LIST_HEAD_INIT(tsk.thread_local_abi_head), +#else +# define INIT_THREAD_LOCAL_ABI(tsk) +#endif + /* * INIT_TASK is used to set up the first task table, touch at * your own risk!. Base=0, limit=0x1fffff (=2MB) @@ -260,6 +267,7 @@ extern struct task_group root_task_group; INIT_VTIME(tsk) \ INIT_NUMA_BALANCING(tsk) \ INIT_KASAN(tsk) \ + INIT_THREAD_LOCAL_ABI(tsk) \ } diff --git a/include/linux/sched.h b/include/linux/sched.h index edad7a4..9cf8917 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2,6 +2,7 @@ #define _LINUX_SCHED_H #include <uapi/linux/sched.h> +#include <uapi/linux/thread_local_abi.h> #include <linux/sched/prio.h> @@ -1375,6 +1376,12 @@ struct tlbflush_unmap_batch { bool writable; }; +struct thread_local_abi_entry { + size_t thread_local_abi_len; + struct thread_local_abi __user *thread_local_abi; + struct list_head entry; +}; + struct task_struct { volatile long state; /* -1 unrunnable, 0 runnable, >0 stopped */ void *stack; @@ -1812,6 +1819,10 @@ struct task_struct { unsigned long task_state_change; #endif int pagefault_disabled; +#ifdef CONFIG_THREAD_LOCAL_ABI + /* list of struct thread_local_abi_entry */ + struct list_head thread_local_abi_head; +#endif /* CPU-specific state of this task */ struct thread_struct thread; /* @@ -3188,4 +3199,33 @@ static inline unsigned long rlimit_max(unsigned int limit) return task_rlimit_max(current, limit); } +#ifdef CONFIG_THREAD_LOCAL_ABI +int thread_local_abi_fork(struct task_struct *t); +void thread_local_abi_execve(struct task_struct *t); +void thread_local_abi_exit(struct task_struct *t); +void thread_local_abi_handle_notify_resume(struct task_struct *t); +static inline bool thread_local_abi_active(struct task_struct *t) +{ + return !list_empty(&t->thread_local_abi_head); +} +#else +static inline int thread_local_abi_fork(struct task_struct *t) +{ + return 0; +} +static inline void thread_local_abi_execve(struct task_struct *t) +{ +} +static inline void thread_local_abi_exit(struct task_struct *t) +{ +} +static inline void thread_local_abi_handle_notify_resume(struct task_struct *t) +{ +} +static inline bool thread_local_abi_active(struct task_struct *t) +{ + return false; +} +#endif + #endif diff --git a/include/uapi/linux/Kbuild b/include/uapi/linux/Kbuild index 628e6e6..5df5460 100644 --- a/include/uapi/linux/Kbuild +++ b/include/uapi/linux/Kbuild @@ -397,6 +397,7 @@ header-y += tcp_metrics.h header-y += telephony.h header-y += termios.h header-y += thermal.h +header-y += thread_local_abi.h header-y += time.h header-y += times.h header-y += timex.h diff --git a/include/uapi/linux/thread_local_abi.h b/include/uapi/linux/thread_local_abi.h new file mode 100644 index 0000000..6487c92 --- /dev/null +++ b/include/uapi/linux/thread_local_abi.h @@ -0,0 +1,37 @@ +#ifndef _UAPI_LINUX_THREAD_LOCAL_ABI_H +#define _UAPI_LINUX_THREAD_LOCAL_ABI_H + +/* + * linux/thread_local_abi.h + * + * thread_local_abi system call API + * + * Copyright (c) 2015 Mathieu Desnoyers <mathieu.desnoy...@efficios.com> + * + * Permission is hereby granted, free of charge, to any person obtaining a copy + * of this software and associated documentation files (the "Software"), to deal + * in the Software without restriction, including without limitation the rights + * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell + * copies of the Software, and to permit persons to whom the Software is + * furnished to do so, subject to the following conditions: + * + * The above copyright notice and this permission notice shall be included in + * all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + */ + +#include <linux/types.h> + +/* This structure is an ABI that can only be extended. */ +struct thread_local_abi { + int32_t cpu; +}; + +#endif /* _UAPI_LINUX_THREAD_LOCAL_ABI_H */ diff --git a/init/Kconfig b/init/Kconfig index c24b6f7..e1a6bf8 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1614,6 +1614,15 @@ config MEMBARRIER If unsure, say Y. +config THREAD_LOCAL_ABI + bool "Enable thread-local ABI" if EXPERT + default y + help + Enable the thread-local ABI system call. It provides a user-space + cache for the current CPU number value. + + If unsure, say Y. + config EMBEDDED bool "Embedded system" option allnoconfig_y diff --git a/kernel/Makefile b/kernel/Makefile index 53abf00..327fbd9 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -103,6 +103,7 @@ obj-$(CONFIG_TORTURE_TEST) += torture.o obj-$(CONFIG_MEMBARRIER) += membarrier.o obj-$(CONFIG_HAS_IOMEM) += memremap.o +obj-$(CONFIG_THREAD_LOCAL_ABI) += thread_local_abi.o $(obj)/configs.o: $(obj)/config_data.h diff --git a/kernel/fork.c b/kernel/fork.c index f97f2c4..02526e8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -252,6 +252,7 @@ void __put_task_struct(struct task_struct *tsk) WARN_ON(tsk == current); cgroup_free(tsk); + thread_local_abi_exit(tsk); task_numa_free(tsk); security_task_free(tsk); exit_creds(tsk); @@ -1554,6 +1555,12 @@ static struct task_struct *copy_process(unsigned long clone_flags, */ copy_seccomp(p); + if (!(clone_flags & CLONE_THREAD)) { + retval = -ENOMEM; + if (thread_local_abi_fork(p)) + goto bad_fork_cancel_cgroup; + } + /* * Process group and session signals need to be delivered to just the * parent before the fork or both the parent and the child after the diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4d568ac..f26babf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2120,6 +2120,9 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p) p->numa_group = NULL; #endif /* CONFIG_NUMA_BALANCING */ +#ifdef CONFIG_THREAD_LOCAL_ABI + INIT_LIST_HEAD(&p->thread_local_abi_head); +#endif } DEFINE_STATIC_KEY_FALSE(sched_numa_balancing); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index efd3bfc..371aa8f 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -957,6 +957,8 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu) { set_task_rq(p, cpu); #ifdef CONFIG_SMP + if (thread_local_abi_active(p)) + set_tsk_thread_flag(p, TIF_NOTIFY_RESUME); /* * After ->cpu is set up to a new value, task_rq_lock(p, ...) can be * successfuly executed on another CPU. We must ensure that updates of diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 0623787..e803824 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -249,3 +249,6 @@ cond_syscall(sys_execveat); /* membarrier */ cond_syscall(sys_membarrier); + +/* thread-local ABI */ +cond_syscall(sys_thread_local_abi); diff --git a/kernel/thread_local_abi.c b/kernel/thread_local_abi.c new file mode 100644 index 0000000..8e60259 --- /dev/null +++ b/kernel/thread_local_abi.c @@ -0,0 +1,174 @@ +/* + * Copyright (C) 2015 Mathieu Desnoyers <mathieu.desnoy...@efficios.com> + * + * thread_local_abi system call + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + */ + +#include <linux/init.h> +#include <linux/sched.h> +#include <linux/uaccess.h> +#include <linux/syscalls.h> +#include <linux/list.h> +#include <linux/slab.h> + +static struct thread_local_abi_entry * + add_thread_entry(struct task_struct *t, + size_t abi_len, + struct thread_local_abi __user *ptr) +{ + struct thread_local_abi_entry *te; + + te = kmalloc(sizeof(*te), GFP_KERNEL); + if (!te) + return NULL; + te->thread_local_abi_len = abi_len; + te->thread_local_abi = ptr; + list_add(&te->entry, &t->thread_local_abi_head); + return te; +} + +static void remove_thread_entry(struct thread_local_abi_entry *te) +{ + list_del(&te->entry); + kfree(te); +} + +static void remove_all_thread_entry(struct task_struct *t) +{ + struct thread_local_abi_entry *te, *te_tmp; + + list_for_each_entry_safe(te, te_tmp, &t->thread_local_abi_head, entry) + remove_thread_entry(te); +} + +static struct thread_local_abi_entry * + find_thread_entry(struct task_struct *t, + struct thread_local_abi __user *ptr) +{ + struct thread_local_abi_entry *te; + + list_for_each_entry(te, &t->thread_local_abi_head, entry) { + if (te->thread_local_abi == ptr) + return te; + } + return NULL; +} + +static int thread_local_abi_update_entry(struct thread_local_abi_entry *te) +{ + if (te->thread_local_abi_len < + offsetof(struct thread_local_abi, cpu) + + sizeof(te->thread_local_abi->cpu)) + return 0; + if (put_user(raw_smp_processor_id(), &te->thread_local_abi->cpu)) { + /* + * Force unregistration of each entry causing + * put_user() errors. + */ + remove_thread_entry(te); + return -1; + } + return 0; + +} + +static int thread_local_abi_update(struct task_struct *t) +{ + struct thread_local_abi_entry *te, *te_tmp; + int err = 0; + + list_for_each_entry_safe(te, te_tmp, &t->thread_local_abi_head, entry) { + if (thread_local_abi_update_entry(te)) + err = -1; + } + return err; +} + +/* + * This resume handler should always be executed between a migration + * triggered by preemption and return to user-space. + */ +void thread_local_abi_handle_notify_resume(struct task_struct *t) +{ + BUG_ON(!thread_local_abi_active(t)); + if (unlikely(t->flags & PF_EXITING)) + return; + if (thread_local_abi_update(t)) + force_sig(SIGSEGV, t); +} + +/* + * If parent process has a thread-local ABI, the child inherits. Only applies + * when forking a process, not a thread. + */ +int thread_local_abi_fork(struct task_struct *t) +{ + struct thread_local_abi_entry *te; + + list_for_each_entry(te, ¤t->thread_local_abi_head, entry) { + if (!add_thread_entry(t, te->thread_local_abi_len, + te->thread_local_abi)) + return -1; + } + return 0; +} + +void thread_local_abi_execve(struct task_struct *t) +{ + remove_all_thread_entry(t); +} + +void thread_local_abi_exit(struct task_struct *t) +{ + remove_all_thread_entry(t); +} + +/* + * sys_thread_local_abi - setup thread-local ABI for caller thread + */ +SYSCALL_DEFINE3(thread_local_abi, struct thread_local_abi __user *, tlap, + size_t, len, int, flags) +{ + size_t minlen; + struct thread_local_abi_entry *te; + + if (flags || !tlap) + return -EINVAL; + te = find_thread_entry(current, tlap); + if (!len) { + /* Unregistration is requested by a 0 len argument. */ + if (!te) + return -ENOENT; + remove_thread_entry(te); + return 0; + } + /* Attempt to register tlap. Check if already there. */ + if (te) + return -EBUSY; + /* Agree on the intersection of userspace and kernel features. */ + minlen = min_t(size_t, len, sizeof(struct thread_local_abi)); + te = add_thread_entry(current, minlen, tlap); + if (!te) + return -ENOMEM; + /* + * Migration walks the thread local abi entry list to see + * whether the notify_resume flag should be set. Therefore, we + * need to ensure that the scheduler sees the list update before + * we update the thread local abi content with the current CPU + * number. + */ + barrier(); /* Add thread entry to list before updating content. */ + if (thread_local_abi_update_entry(te)) + return -EFAULT; + return minlen; +} -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
