From patchwork Wed Sep 23 23:36:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Peter Oskolkov X-Patchwork-Id: 11795803 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C15CB16BC for ; Wed, 23 Sep 2020 23:36:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9AFB5212CC for ; Wed, 23 Sep 2020 23:36:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="g1rhN4vO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726562AbgIWXgY (ORCPT ); Wed, 23 Sep 2020 19:36:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726537AbgIWXgX (ORCPT ); Wed, 23 Sep 2020 19:36:23 -0400 Received: from mail-qt1-x84a.google.com (mail-qt1-x84a.google.com [IPv6:2607:f8b0:4864:20::84a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1763C0613D1 for ; Wed, 23 Sep 2020 16:36:22 -0700 (PDT) Received: by mail-qt1-x84a.google.com with SMTP id a14so1150352qtp.15 for ; Wed, 23 Sep 2020 16:36:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=/0tlybrj84QUY6udBfoxtR3AJN5XaEaEXm9yNo6y3z4=; b=g1rhN4vOrM2MAe0lVP2XRTkO37kHs/b/IyFRHG0RGi4JSJ/yvFiH3qHC5uFAmapLLy S1hPpkuyJ83Ekk+J+MTRxGJu8zry5G48LWr4o0D+9GHJAqg2P2STRw60VkMTImigYsBG 0NpPlVK3Wz1zYbN1qrMTz6wZV5Ddg1wEH6rYuNNC6j+yToL1x7WqSRSuJ4haM200e47n bPLxRENCXSd2GZ76HJpYdi9D5lxSt5SVSvTPbW4OSg0Fqy7R53oHzs+cmWVPGT/E8OF1 vUvAtlYCfvWvC8Lge6MH/a26UyZMXvAFSaKgeXTqJ0WHy6/mjEo2Tv3kAr+gpn0MxY2Z OzmQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=/0tlybrj84QUY6udBfoxtR3AJN5XaEaEXm9yNo6y3z4=; b=E1af+94ukCx+kifRB/0jbI+MtFa5uyz5++ZzG3oAte8yXGZTTjmNn6iHGz/IdugCry J9D/gKRztgJdfrtrSSjDGTy5RCa4ArfC4GXPrrj+59E31MfG+XkZEjtcBJlgi/aI0B9B SRVobylXDp2/RLoYo5hzdjzDsca2NOCg8hG6X9s62kVQ9owGWjRy6uTd+3M/PGxq9VB0 Dl3663WvPc5TUEB7s6d7b7p3t4Xvna5mUc2/TvSjmiVK+ho+UD2xrP/cN2s0wjxUElQb Tq9RgXGk+fbvWBqMxbEu2glBUzeCq7PXJ5kMj9b1pP1dr6BNKnm7n1pZUV0YCT1TQhXz yy/w== X-Gm-Message-State: AOAM532xRWY2jxFmiwGfzPvLxMUit0UzbxaShfTDLoILemxlSK3LlQh7 TiwGzYsVzR8BCFvMbQaxXFkB8NMW X-Google-Smtp-Source: ABdhPJy+7oMufpRAku3l9CJ1naU8D/RA/Eh5jpQ51DF0fphPaQ/TnNySwhm1AjhekNgQBE1EAD/No7i1 Sender: "posk via sendgmr" X-Received: from posk.svl.corp.google.com ([2620:15c:2cd:202:7220:84ff:fe09:7598]) (user=posk job=sendgmr) by 2002:ad4:58c7:: with SMTP id dh7mr2654523qvb.20.1600904181978; Wed, 23 Sep 2020 16:36:21 -0700 (PDT) Date: Wed, 23 Sep 2020 16:36:16 -0700 Message-Id: <20200923233618.2572849-1-posk@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.709.gb0816b6eb0-goog Subject: [PATCH v8 1/3] rseq/membarrier: add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ From: Peter Oskolkov To: Mathieu Desnoyers , "Paul E . McKenney" , Peter Zijlstra , Boqun Feng , linux-kernel@vger.kernel.org Cc: Paul Turner , Chris Kennelly , Peter Oskolkov , Shuah Khan , linux-kselftest@vger.kernel.org, Peter Oskolkov Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org This patchset is based on Google-internal RSEQ work done by Paul Turner and Andrew Hunter. When working with per-CPU RSEQ-based memory allocations, it is sometimes important to make sure that a global memory location is no longer accessed from RSEQ critical sections. For example, there can be two per-CPU lists, one is "active" and accessed per-CPU, while another one is inactive and worked on asynchronously "off CPU" (e.g. garbage collection is performed). Then at some point the two lists are swapped, and a fast RCU-like mechanism is required to make sure that the previously active list is no longer accessed. This patch introduces such a mechanism: in short, membarrier() syscall issues an IPI to a CPU, restarting a potentially active RSEQ critical section on the CPU. v1->v2: - removed the ability to IPI all CPUs in a single sycall; - use task->mm rather than task->group_leader to identify tasks belonging to the same process. v2->v3: - re-added the ability to IPI all CPUs in a single syscall; - integrated with membarrier_private_expedited() to make sure only CPUs running tasks with the same mm as the current task are interrupted; - also added MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ; - flags in membarrier_private_expedited are never actually bit flags but always distinct values (i.e. never two flags are combined), so I modified bit testing to full equation comparison for simplicity (otherwise the code needs to work when several bits are set, for example). v3->v4: - added the third parameter to membarrier syscall: @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, then @cpu_id indicates the cpu on which RSEQ CS should be restarted. v4->v5: - added @cpu_id parameter to sys_membarrier in syscalls.h. v5->v6: - made membarrier_private_expedited more efficient in a single-cpu case; - a couple of minor refactorings. v6->v7: - made @flags an unsigned int in sys_membarrier; - a couple of minor refactorings. v7->v8: - replaced BUG_ON with WARN_ON_ONCE in membarrier.c. The second patch in the patchset adds a selftest of this feature. Signed-off-by: Peter Oskolkov Acked-by: Mathieu Desnoyers --- include/linux/sched/mm.h | 3 + include/linux/syscalls.h | 2 +- include/uapi/linux/membarrier.h | 26 ++++++ kernel/sched/membarrier.c | 136 +++++++++++++++++++++++++------- 4 files changed, 136 insertions(+), 31 deletions(-) diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index f889e332912f..15bfb06f2884 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -348,10 +348,13 @@ enum { MEMBARRIER_STATE_GLOBAL_EXPEDITED = (1U << 3), MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY = (1U << 4), MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE = (1U << 5), + MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY = (1U << 6), + MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ = (1U << 7), }; enum { MEMBARRIER_FLAG_SYNC_CORE = (1U << 0), + MEMBARRIER_FLAG_RSEQ = (1U << 1), }; #ifdef CONFIG_ARCH_HAS_MEMBARRIER_CALLBACKS diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 75ac7f8ae93c..466c993e52bf 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -974,7 +974,7 @@ asmlinkage long sys_execveat(int dfd, const char __user *filename, const char __user *const __user *argv, const char __user *const __user *envp, int flags); asmlinkage long sys_userfaultfd(int flags); -asmlinkage long sys_membarrier(int cmd, int flags); +asmlinkage long sys_membarrier(int cmd, int flags, int cpu_id); asmlinkage long sys_mlock2(unsigned long start, size_t len, int flags); asmlinkage long sys_copy_file_range(int fd_in, loff_t __user *off_in, int fd_out, loff_t __user *off_out, diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h index 5891d7614c8c..737605897f36 100644 --- a/include/uapi/linux/membarrier.h +++ b/include/uapi/linux/membarrier.h @@ -114,6 +114,26 @@ * If this command is not implemented by an * architecture, -EINVAL is returned. * Returns 0 on success. + * @MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: + * Ensure the caller thread, upon return from + * system call, that all its running thread + * siblings have any currently running rseq + * critical sections restarted if @flags + * parameter is 0; if @flags parameter is + * MEMBARRIER_CMD_FLAG_CPU, + * then this operation is performed only + * on CPU indicated by @cpu_id. If this command is + * not implemented by an architecture, -EINVAL + * is returned. A process needs to register its + * intent to use the private expedited rseq + * command prior to using it, otherwise + * this command returns -EPERM. + * @MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: + * Register the process intent to use + * MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ. + * If this command is not implemented by an + * architecture, -EINVAL is returned. + * Returns 0 on success. * @MEMBARRIER_CMD_SHARED: * Alias to MEMBARRIER_CMD_GLOBAL. Provided for * header backward compatibility. @@ -131,9 +151,15 @@ enum membarrier_cmd { MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4), MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE = (1 << 5), MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE = (1 << 6), + MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ = (1 << 7), + MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ = (1 << 8), /* Alias for header backward compatibility. */ MEMBARRIER_CMD_SHARED = MEMBARRIER_CMD_GLOBAL, }; +enum membarrier_cmd_flag { + MEMBARRIER_CMD_FLAG_CPU = (1 << 0), +}; + #endif /* _UAPI_LINUX_MEMBARRIER_H */ diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 168479a7d61b..e23e74d52db5 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -18,6 +18,14 @@ #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK 0 #endif +#ifdef CONFIG_RSEQ +#define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK \ + (MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ \ + | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ_BITMASK) +#else +#define MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ_BITMASK 0 +#endif + #define MEMBARRIER_CMD_BITMASK \ (MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED \ | MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED \ @@ -30,6 +38,11 @@ static void ipi_mb(void *info) smp_mb(); /* IPIs should be serializing but paranoid. */ } +static void ipi_rseq(void *info) +{ + rseq_preempt(current); +} + static void ipi_sync_rq_state(void *info) { struct mm_struct *mm = (struct mm_struct *) info; @@ -129,19 +142,27 @@ static int membarrier_global_expedited(void) return 0; } -static int membarrier_private_expedited(int flags) +static int membarrier_private_expedited(int flags, int cpu_id) { - int cpu; cpumask_var_t tmpmask; struct mm_struct *mm = current->mm; + smp_call_func_t ipi_func = ipi_mb; - if (flags & MEMBARRIER_FLAG_SYNC_CORE) { + if (flags == MEMBARRIER_FLAG_SYNC_CORE) { if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) return -EINVAL; if (!(atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY)) return -EPERM; + } else if (flags == MEMBARRIER_FLAG_RSEQ) { + if (!IS_ENABLED(CONFIG_RSEQ)) + return -EINVAL; + if (!(atomic_read(&mm->membarrier_state) & + MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY)) + return -EPERM; + ipi_func = ipi_rseq; } else { + WARN_ON_ONCE(flags); if (!(atomic_read(&mm->membarrier_state) & MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY)) return -EPERM; @@ -156,35 +177,59 @@ static int membarrier_private_expedited(int flags) */ smp_mb(); /* system call entry is not a mb. */ - if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) + if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL)) return -ENOMEM; cpus_read_lock(); - rcu_read_lock(); - for_each_online_cpu(cpu) { + + if (cpu_id >= 0) { struct task_struct *p; - /* - * Skipping the current CPU is OK even through we can be - * migrated at any point. The current CPU, at the point - * where we read raw_smp_processor_id(), is ensured to - * be in program order with respect to the caller - * thread. Therefore, we can skip this CPU from the - * iteration. - */ - if (cpu == raw_smp_processor_id()) - continue; - p = rcu_dereference(cpu_rq(cpu)->curr); - if (p && p->mm == mm) - __cpumask_set_cpu(cpu, tmpmask); + if (cpu_id >= nr_cpu_ids || !cpu_online(cpu_id)) + goto out; + if (cpu_id == raw_smp_processor_id()) + goto out; + rcu_read_lock(); + p = rcu_dereference(cpu_rq(cpu_id)->curr); + if (!p || p->mm != mm) { + rcu_read_unlock(); + goto out; + } + rcu_read_unlock(); + } else { + int cpu; + + rcu_read_lock(); + for_each_online_cpu(cpu) { + struct task_struct *p; + + /* + * Skipping the current CPU is OK even through we can be + * migrated at any point. The current CPU, at the point + * where we read raw_smp_processor_id(), is ensured to + * be in program order with respect to the caller + * thread. Therefore, we can skip this CPU from the + * iteration. + */ + if (cpu == raw_smp_processor_id()) + continue; + p = rcu_dereference(cpu_rq(cpu)->curr); + if (p && p->mm == mm) + __cpumask_set_cpu(cpu, tmpmask); + } + rcu_read_unlock(); } - rcu_read_unlock(); preempt_disable(); - smp_call_function_many(tmpmask, ipi_mb, NULL, 1); + if (cpu_id >= 0) + smp_call_function_single(cpu_id, ipi_func, NULL, 1); + else + smp_call_function_many(tmpmask, ipi_func, NULL, 1); preempt_enable(); - free_cpumask_var(tmpmask); +out: + if (cpu_id < 0) + free_cpumask_var(tmpmask); cpus_read_unlock(); /* @@ -283,11 +328,18 @@ static int membarrier_register_private_expedited(int flags) set_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED, ret; - if (flags & MEMBARRIER_FLAG_SYNC_CORE) { + if (flags == MEMBARRIER_FLAG_SYNC_CORE) { if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE)) return -EINVAL; ready_state = MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY; + } else if (flags == MEMBARRIER_FLAG_RSEQ) { + if (!IS_ENABLED(CONFIG_RSEQ)) + return -EINVAL; + ready_state = + MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY; + } else { + WARN_ON_ONCE(flags); } /* @@ -299,6 +351,8 @@ static int membarrier_register_private_expedited(int flags) return 0; if (flags & MEMBARRIER_FLAG_SYNC_CORE) set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE; + if (flags & MEMBARRIER_FLAG_RSEQ) + set_state |= MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ; atomic_or(set_state, &mm->membarrier_state); ret = sync_runqueues_membarrier_state(mm); if (ret) @@ -310,8 +364,15 @@ static int membarrier_register_private_expedited(int flags) /** * sys_membarrier - issue memory barriers on a set of threads - * @cmd: Takes command values defined in enum membarrier_cmd. - * @flags: Currently needs to be 0. For future extensions. + * @cmd: Takes command values defined in enum membarrier_cmd. + * @flags: Currently needs to be 0 for all commands other than + * MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: in the latter + * case it can be MEMBARRIER_CMD_FLAG_CPU, indicating that @cpu_id + * contains the CPU on which to interrupt (= restart) + * the RSEQ critical section. + * @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which + * RSEQ CS should be interrupted (@cmd must be + * MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ). * * If this system call is not implemented, -ENOSYS is returned. If the * command specified does not exist, not available on the running @@ -337,10 +398,21 @@ static int membarrier_register_private_expedited(int flags) * smp_mb() X O O * sys_membarrier() O O O */ -SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) +SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id) { - if (unlikely(flags)) - return -EINVAL; + switch (cmd) { + case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: + if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU)) + return -EINVAL; + break; + default: + if (unlikely(flags)) + return -EINVAL; + } + + if (!(flags & MEMBARRIER_CMD_FLAG_CPU)) + cpu_id = -1; + switch (cmd) { case MEMBARRIER_CMD_QUERY: { @@ -362,13 +434,17 @@ SYSCALL_DEFINE2(membarrier, int, cmd, int, flags) case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED: return membarrier_register_global_expedited(); case MEMBARRIER_CMD_PRIVATE_EXPEDITED: - return membarrier_private_expedited(0); + return membarrier_private_expedited(0, cpu_id); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED: return membarrier_register_private_expedited(0); case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE: - return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE); + return membarrier_private_expedited(MEMBARRIER_FLAG_SYNC_CORE, cpu_id); case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE: return membarrier_register_private_expedited(MEMBARRIER_FLAG_SYNC_CORE); + case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ: + return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, cpu_id); + case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ: + return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ); default: return -EINVAL; }