From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx4/3cMHWUlX2bAGgSsIf7ThIkjpY2QKm9JZPdUN3/GIgwpJW9u0eoBrb+s604LbORUtuzxG9 ARC-Seal: i=1; a=rsa-sha256; t=1523931074; cv=none; d=google.com; s=arc-20160816; b=osrOBTTsFAIqSN/lKrMRQSqvBXQjRr+SkeXTMnmpzwPugWvkpNXsAkgPV6ncowRYk7 g4uzd60RKLx1HIPHUFByBn6irZ6ea5+ZcU5wc0rrTxaP7gVmWum3od7Zw6Qg3XekRgt4 icV3gCjBqVEi8C6JaDbcFi6KnhSHI48VYqCWCcYhrQ4AFE7E9+ws2sEtsWecB7brI13m KUpfcQX8wVAct8QJN+zc/WP1EQh5tZn6FsoU0CNPfmObCqXsArsWGj7p2GZOrHQb1L2+ 3E/czoFHPNKnlHAy9PjsoOXHaUtPA/wyAfLSSZVBCFuD50hOo59tjT0eMUbMBZmcIGrT xxGQ== 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=wPEWxxtosMsA1eexMsbPczFagEUs47O3cT6besjPwds=; b=yj+Yf4jzUU170GvLELVgAXsueWhiP0zCn+jEj5kjvsc66O8YPA1kHoz5ijA4bhc4HX Ein5ndb55Lcd794Ko8K7c3toH4/PaNk/V5s5KnOG7/EWnl+1AJIRmJqF7muuGG8oVzPh Cd17wSJjm5QEaq7O4GOLwrnSXi5scfhBtnHp0SSkDu7pTbMx97feDW9FtKHupqYPG2Kq ZRQyWxqcr4/cq6Jh8z8bUy96EgqjLQ5ywfgI1j86nwCayVX/7T5nWiYx7/yNE7HubsNS NM16gGQk4NmFDifnnD5oIbfY7SAZPJ7wspc9cDxb6pFWf2r+8tPyz8EtEVq8EOcB/dzY ZxDQ== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of alastair@au1.ibm.com designates 148.163.158.5 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 148.163.158.5 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 3/7] powerpc: use task_pid_nr() for TID allocation Date: Tue, 17 Apr 2018 12:09:46 +1000 X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180417020950.21446-1-alastair@au1.ibm.com> References: <20180417020950.21446-1-alastair@au1.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18041702-0020-0000-0000-00000412A93B X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18041702-0021-0000-0000-000042A6E624 Message-Id: <20180417020950.21446-4-alastair@au1.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-17_01:,, 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-1804170020 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1597957550726280592?= X-GMAIL-MSGID: =?utf-8?q?1597957550726280592?= 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/kernel/process.c | 97 +------------------------------------------ 1 file changed, 1 insertion(+), 96 deletions(-) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index a3e0a3e06d5a..56ff7eb5ff79 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=unavailable 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 E1AFF7DE74 for ; Tue, 17 Apr 2018 02:11:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752915AbeDQCLU (ORCPT ); Mon, 16 Apr 2018 22:11:20 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42808 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752955AbeDQCLO (ORCPT ); Mon, 16 Apr 2018 22:11:14 -0400 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w3H291il094377 for ; Mon, 16 Apr 2018 22:11:13 -0400 Received: from e06smtp15.uk.ibm.com (e06smtp15.uk.ibm.com [195.75.94.111]) by mx0b-001b2d01.pphosted.com with ESMTP id 2hd59gwq6f-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Mon, 16 Apr 2018 22:11:13 -0400 Received: from localhost by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Tue, 17 Apr 2018 03:11:07 +0100 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w3H2B6hq57606268; Tue, 17 Apr 2018 02:11:06 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 10669AE053; Tue, 17 Apr 2018 03:00:57 +0100 (BST) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6AB23AE055; Tue, 17 Apr 2018 03:00:56 +0100 (BST) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 17 Apr 2018 03:00:56 +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 5AF8BA027F; Tue, 17 Apr 2018 12:11:04 +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 3/7] powerpc: use task_pid_nr() for TID allocation Date: Tue, 17 Apr 2018 12:09:46 +1000 X-Mailer: git-send-email 2.14.3 In-Reply-To: <20180417020950.21446-1-alastair@au1.ibm.com> References: <20180417020950.21446-1-alastair@au1.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18041702-0020-0000-0000-00000412A93B X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18041702-0021-0000-0000-000042A6E624 Message-Id: <20180417020950.21446-4-alastair@au1.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-04-17_01:,, 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-1804170020 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/kernel/process.c | 97 +------------------------------------------ 1 file changed, 1 insertion(+), 96 deletions(-) diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index a3e0a3e06d5a..56ff7eb5ff79 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