From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx49VaZpPx0PtUb1wYcylapZRUd4xuQ6/WUOh0Pim/BMb72sPci2Uw4Sl4ZxgCA+wVcec+59A ARC-Seal: i=1; a=rsa-sha256; t=1524013869; cv=none; d=google.com; s=arc-20160816; b=WJh4YuV5oIWrNbc1vwoNWuqM0LoJBc7t0QAd9AAecvA93jnhQ0zR8yJPXhNpIZ+x/M ffqw8N7a1xpdWFo4SKlQlJCa/Atw0JKZowlNJ9DvnR++Vf5l9LEZ5tj7ukm5QfMDoViN gAXyfgQRI57Z13G2GGpHXh/2NRr+2SaaSS493F9yRBJxaxdjVu+N6q9T8mdE86iduymc PlvNmRHv6e8/dDmRWwXgWd2TIB9EaRbEyJrlNwwWn3JHk8fN0p/tS7k8Tc9VNn5hGOkc vhLlO9CVjwD37FNfdRWLhugEDRyqyogxP/8pgbRQt026SYhMVrUU2pmGTRMnSC0BAbcL CFAQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=message-id:references:in-reply-to:date:subject:cc:to:from :arc-authentication-results; bh=YcjszSDnZA/xcxWAEOhVZP95Su3zNwJyl6jp43dV078=; b=ZpNGc5ar5XtwS2rf8mOANYSx4AtDP9h5rxDaqdSlgLEKuJL+nLhwM5eUomSP9feg6O tIRFHEo0R/nRT5S4AS/qs6fozPkWhSyu8kq09GnWFil1O4Dt4GCJpGqfLwUEhGWEuXYL JXTY6fB+faMLr3uwU9hPxbc1BBpYK+2ZsIWudpnIdynmRnqymjYo/z51PFMcJTjTZ0J4 NytkMaL409FX0VjKI1vPOILTKf/SkR6wWrzG9v7Yy/fpwKw7wQPCIHGWblYJmHbJonQ4 vseuB/NVUlNf24u1oGIBKu+ppaEfGSi3B0k6Hdt3+515M+uFp3mzzabEv+WgC8gUhdL8 DoPA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of alastair@au1.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=alastair@au1.ibm.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=ibm.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of alastair@au1.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=alastair@au1.ibm.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=ibm.com From: "Alastair D'Silva" To: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, mikey@neuling.org, vaibhav@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, malat@debian.org, felix@linux.vnet.ibm.com, pombredanne@nexb.com, sukadev@linux.vnet.ibm.com, npiggin@gmail.com, gregkh@linuxfoundation.org, arnd@arndb.de, andrew.donnellan@au1.ibm.com, fbarrat@linux.vnet.ibm.com, corbet@lwn.net, "Alastair D'Silva" Subject: [PATCH v2 3/7] powerpc: use task_pid_nr() for TID allocation Date: Wed, 18 Apr 2018 11:08:06 +1000 X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180418010810.30937-1-alastair@au1.ibm.com> References: <20180417020950.21446-1-alastair@au1.ibm.com> <20180418010810.30937-1-alastair@au1.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18041801-0008-0000-0000-000004EC75A7 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18041801-0009-0000-0000-00001E807C82 Message-Id: <20180418010810.30937-4-alastair@au1.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-17_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=3 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804180008 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1597957550726280592?= X-GMAIL-MSGID: =?utf-8?q?1598044367011827704?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Alastair D'Silva The current implementation of TID allocation, using a global IDR, may result in an errant process starving the system of available TIDs. Instead, use task_pid_nr(), as mentioned by the original author. The scenario described which prevented it's use is not applicable, as set_thread_tidr can only be called after the task struct has been populated. Signed-off-by: Alastair D'Silva --- arch/powerpc/include/asm/switch_to.h | 1 - arch/powerpc/kernel/process.c | 97 +----------------------------------- 2 files changed, 1 insertion(+), 97 deletions(-) diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index be8c9fa23983..5b03d8a82409 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -94,6 +94,5 @@ static inline void clear_task_ebb(struct task_struct *t) extern int set_thread_uses_vas(void); extern int set_thread_tidr(struct task_struct *t); -extern void clear_thread_tidr(struct task_struct *t); #endif /* _ASM_POWERPC_SWITCH_TO_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 3b00da47699b..87f047fd2762 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1496,103 +1496,12 @@ int set_thread_uses_vas(void) } #ifdef CONFIG_PPC64 -static DEFINE_SPINLOCK(vas_thread_id_lock); -static DEFINE_IDA(vas_thread_ida); - -/* - * We need to assign a unique thread id to each thread in a process. - * - * This thread id, referred to as TIDR, and separate from the Linux's tgid, - * is intended to be used to direct an ASB_Notify from the hardware to the - * thread, when a suitable event occurs in the system. - * - * One such event is a "paste" instruction in the context of Fast Thread - * Wakeup (aka Core-to-core wake up in the Virtual Accelerator Switchboard - * (VAS) in POWER9. - * - * To get a unique TIDR per process we could simply reuse task_pid_nr() but - * the problem is that task_pid_nr() is not yet available copy_thread() is - * called. Fixing that would require changing more intrusive arch-neutral - * code in code path in copy_process()?. - * - * Further, to assign unique TIDRs within each process, we need an atomic - * field (or an IDR) in task_struct, which again intrudes into the arch- - * neutral code. So try to assign globally unique TIDRs for now. - * - * NOTE: TIDR 0 indicates that the thread does not need a TIDR value. - * For now, only threads that expect to be notified by the VAS - * hardware need a TIDR value and we assign values > 0 for those. - */ -#define MAX_THREAD_CONTEXT ((1 << 16) - 1) -static int assign_thread_tidr(void) -{ - int index; - int err; - unsigned long flags; - -again: - if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL)) - return -ENOMEM; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - err = ida_get_new_above(&vas_thread_ida, 1, &index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - - if (err == -EAGAIN) - goto again; - else if (err) - return err; - - if (index > MAX_THREAD_CONTEXT) { - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - return -ENOMEM; - } - - return index; -} - -static void free_thread_tidr(int id) -{ - unsigned long flags; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, id); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); -} - -/* - * Clear any TIDR value assigned to this thread. - */ -void clear_thread_tidr(struct task_struct *t) -{ - if (!t->thread.tidr) - return; - - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) { - WARN_ON_ONCE(1); - return; - } - - mtspr(SPRN_TIDR, 0); - free_thread_tidr(t->thread.tidr); - t->thread.tidr = 0; -} - -void arch_release_task_struct(struct task_struct *t) -{ - clear_thread_tidr(t); -} - /* * Assign a unique TIDR (thread id) for task @t and set it in the thread * structure. For now, we only support setting TIDR for 'current' task. */ int set_thread_tidr(struct task_struct *t) { - int rc; - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) return -EINVAL; @@ -1602,11 +1511,7 @@ int set_thread_tidr(struct task_struct *t) if (t->thread.tidr) return 0; - rc = assign_thread_tidr(); - if (rc < 0) - return rc; - - t->thread.tidr = rc; + t->thread.tidr = (u16)task_pid_nr(t); mtspr(SPRN_TIDR, t->thread.tidr); return 0; -- 2.14.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 16FCB7E279 for ; Wed, 18 Apr 2018 01:11:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752736AbeDRBLM (ORCPT ); Tue, 17 Apr 2018 21:11:12 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:51002 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753316AbeDRBLJ (ORCPT ); Tue, 17 Apr 2018 21:11:09 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w3I1AqbC015897 for ; Tue, 17 Apr 2018 21:11:08 -0400 Received: from e06smtp12.uk.ibm.com (e06smtp12.uk.ibm.com [195.75.94.108]) by mx0a-001b2d01.pphosted.com with ESMTP id 2hds23phg6-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Tue, 17 Apr 2018 21:11:08 -0400 Received: from localhost by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Wed, 18 Apr 2018 02:11:02 +0100 Received: from d06av24.portsmouth.uk.ibm.com (mk.ibm.com [9.149.105.60]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w3I1B1f456754418; Wed, 18 Apr 2018 01:11:01 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7401642042; Wed, 18 Apr 2018 02:02:34 +0100 (BST) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id CE55E42041; Wed, 18 Apr 2018 02:02:33 +0100 (BST) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 18 Apr 2018 02:02:33 +0100 (BST) Received: from adsilva.ozlabs.ibm.com (haven.au.ibm.com [9.192.254.114]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.au.ibm.com (Postfix) with ESMTPSA id A8813A0282; Wed, 18 Apr 2018 11:10:59 +1000 (AEST) From: "Alastair D'Silva" To: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, mikey@neuling.org, vaibhav@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, malat@debian.org, felix@linux.vnet.ibm.com, pombredanne@nexb.com, sukadev@linux.vnet.ibm.com, npiggin@gmail.com, gregkh@linuxfoundation.org, arnd@arndb.de, andrew.donnellan@au1.ibm.com, fbarrat@linux.vnet.ibm.com, corbet@lwn.net, "Alastair D'Silva" Subject: [PATCH v2 3/7] powerpc: use task_pid_nr() for TID allocation Date: Wed, 18 Apr 2018 11:08:06 +1000 X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180418010810.30937-1-alastair@au1.ibm.com> References: <20180417020950.21446-1-alastair@au1.ibm.com> <20180418010810.30937-1-alastair@au1.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18041801-0008-0000-0000-000004EC75A7 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18041801-0009-0000-0000-00001E807C82 Message-Id: <20180418010810.30937-4-alastair@au1.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-17_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=3 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804180008 Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org From: Alastair D'Silva The current implementation of TID allocation, using a global IDR, may result in an errant process starving the system of available TIDs. Instead, use task_pid_nr(), as mentioned by the original author. The scenario described which prevented it's use is not applicable, as set_thread_tidr can only be called after the task struct has been populated. Signed-off-by: Alastair D'Silva --- arch/powerpc/include/asm/switch_to.h | 1 - arch/powerpc/kernel/process.c | 97 +----------------------------------- 2 files changed, 1 insertion(+), 97 deletions(-) diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index be8c9fa23983..5b03d8a82409 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -94,6 +94,5 @@ static inline void clear_task_ebb(struct task_struct *t) extern int set_thread_uses_vas(void); extern int set_thread_tidr(struct task_struct *t); -extern void clear_thread_tidr(struct task_struct *t); #endif /* _ASM_POWERPC_SWITCH_TO_H */ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 3b00da47699b..87f047fd2762 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1496,103 +1496,12 @@ int set_thread_uses_vas(void) } #ifdef CONFIG_PPC64 -static DEFINE_SPINLOCK(vas_thread_id_lock); -static DEFINE_IDA(vas_thread_ida); - -/* - * We need to assign a unique thread id to each thread in a process. - * - * This thread id, referred to as TIDR, and separate from the Linux's tgid, - * is intended to be used to direct an ASB_Notify from the hardware to the - * thread, when a suitable event occurs in the system. - * - * One such event is a "paste" instruction in the context of Fast Thread - * Wakeup (aka Core-to-core wake up in the Virtual Accelerator Switchboard - * (VAS) in POWER9. - * - * To get a unique TIDR per process we could simply reuse task_pid_nr() but - * the problem is that task_pid_nr() is not yet available copy_thread() is - * called. Fixing that would require changing more intrusive arch-neutral - * code in code path in copy_process()?. - * - * Further, to assign unique TIDRs within each process, we need an atomic - * field (or an IDR) in task_struct, which again intrudes into the arch- - * neutral code. So try to assign globally unique TIDRs for now. - * - * NOTE: TIDR 0 indicates that the thread does not need a TIDR value. - * For now, only threads that expect to be notified by the VAS - * hardware need a TIDR value and we assign values > 0 for those. - */ -#define MAX_THREAD_CONTEXT ((1 << 16) - 1) -static int assign_thread_tidr(void) -{ - int index; - int err; - unsigned long flags; - -again: - if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL)) - return -ENOMEM; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - err = ida_get_new_above(&vas_thread_ida, 1, &index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - - if (err == -EAGAIN) - goto again; - else if (err) - return err; - - if (index > MAX_THREAD_CONTEXT) { - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, index); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); - return -ENOMEM; - } - - return index; -} - -static void free_thread_tidr(int id) -{ - unsigned long flags; - - spin_lock_irqsave(&vas_thread_id_lock, flags); - ida_remove(&vas_thread_ida, id); - spin_unlock_irqrestore(&vas_thread_id_lock, flags); -} - -/* - * Clear any TIDR value assigned to this thread. - */ -void clear_thread_tidr(struct task_struct *t) -{ - if (!t->thread.tidr) - return; - - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) { - WARN_ON_ONCE(1); - return; - } - - mtspr(SPRN_TIDR, 0); - free_thread_tidr(t->thread.tidr); - t->thread.tidr = 0; -} - -void arch_release_task_struct(struct task_struct *t) -{ - clear_thread_tidr(t); -} - /* * Assign a unique TIDR (thread id) for task @t and set it in the thread * structure. For now, we only support setting TIDR for 'current' task. */ int set_thread_tidr(struct task_struct *t) { - int rc; - if (!cpu_has_feature(CPU_FTR_P9_TIDR)) return -EINVAL; @@ -1602,11 +1511,7 @@ int set_thread_tidr(struct task_struct *t) if (t->thread.tidr) return 0; - rc = assign_thread_tidr(); - if (rc < 0) - return rc; - - t->thread.tidr = rc; + t->thread.tidr = (u16)task_pid_nr(t); mtspr(SPRN_TIDR, t->thread.tidr); return 0; -- 2.14.3 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html