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Shenoy" , "Chen Yu" , Julia Lawall , "Sebastian Andrzej Siewior" Subject: [RFC PATCH v2 3/5] softirq: Mask reads of softirq_ctrl.cnt with SOFTIRQ_MASK for PREEMPT_RT Date: Wed, 4 Sep 2024 11:12:21 +0000 Message-ID: <20240904111223.1035-4-kprateek.nayak@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240904111223.1035-1-kprateek.nayak@amd.com> References: <20240904111223.1035-1-kprateek.nayak@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: SATLEXMB04.amd.com (10.181.40.145) To SATLEXMB03.amd.com (10.181.40.144) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B070:EE_|CY5PR12MB6059:EE_ X-MS-Office365-Filtering-Correlation-Id: a5a8c265-feb4-4eb7-d231-08dcccd29edb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|1800799024|376014|7416014|82310400026|921020; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?7r8g6Ok80i4ChTee7BqZLfinIavihPDb9lzY75btlgWYg9gT33pql83HiMjT?= =?us-ascii?Q?/kbR2jkLwSg3nD6zgR71Cd4uSA0ozpyzPYRH8vdYnxu3cHpXmK8iuCfatDAD?= =?us-ascii?Q?wLRAzLAyCgTQ/+Zk/qFsgh+DtfwMJN5Jpe4fGDTGpVNlRYOQJ4e796RCE/Sh?= =?us-ascii?Q?wJQ+eCCmSi7uo+mPpFfUV2BWt09mbn33v6xC1BcXXjFc45RtEWEWmkNxaXIX?= =?us-ascii?Q?M3nu34zLICdjSLQ1aH0X3mKNL6MMrSYaOStMBy1ndKNpM5Sw2a63bTYFgRTY?= =?us-ascii?Q?AaUSQ0TgCzyZlINsFiZtbMXyTvQzk/5wZZXnJl+z+UEFkMOQxx90kqHiwwxU?= =?us-ascii?Q?ddRu1mPNh/cbU8OpT+9SmKFhxkjhRlJuMVaR7N976JaIhGSz3KZ2DTMjAH29?= =?us-ascii?Q?yxLvyigM0Cd2nDz/QNyNbJrkxdkyrN4euL38XpMDtvg7V7+x4u2/QuuXk+cV?= =?us-ascii?Q?9cN4/mOALj+Iq7WYsArmEWMVzyUgGl0S/63g7dSCONOHPlf6AJQqhIXSsvA0?= =?us-ascii?Q?q97nNkECUJ2NiyrmXx+QWZrcUkWGQwNGmm9Wsaw+ur9Pir+xP5aGslyKhWxu?= =?us-ascii?Q?NYJSwCwIxg3LDoyNBjYAr/LWm7iny5BJd/Ii9t95H5gGJ6pdvIU3IqMeIVd7?= =?us-ascii?Q?i9wIkgSqk1STBs98vcMTHLQ7nk5nBUJkwaPnS7vluPC5+0LckdMgS1OAuUZi?= =?us-ascii?Q?6Hj5BQyFHsP//Q1p/UJDq7NScp3nhqwRzT6MFBy+ZWbSWNPI+xdZ6Q+cToG5?= =?us-ascii?Q?dQ72B12NGboP8gy/lnWXa7bNtpWD1uBbI5/7pCtHhEDntMrvWRnnhjwo5L38?= =?us-ascii?Q?Z15tMEBn7IzC9gyx5hoNEWj4xkw0HIla9Jd0YfJ6Nhtmv6IdVmbYXC2gous+?= =?us-ascii?Q?OEF9LaZ/R2IRWONGJGs+OIobaulCv9pSobYIzw1YmRAHljSKoq0QOrZdTwP0?= =?us-ascii?Q?YISTX/aehgGT4nors2Gcru3GPi05p3ovUvjaDMn1PRg3HUGWd+plXMJgbfcy?= =?us-ascii?Q?Cs2MU0u0Um0yCYJry09oqBxQv+pirztZXsU0z7epKlzqJB/pQKaH1Bpm+8Yd?= =?us-ascii?Q?aZqnYytvJgdipUKnSCpxaf69n3IiDv8WHVAodNP5enELahfYX7TPe5PltfDh?= =?us-ascii?Q?+BKuyH66W0/mYJCGiKUjhs1lIMqrWBm8Kf1VQhNi5U5/L0mxr7r9kDKVBjP1?= =?us-ascii?Q?OsC3qiAME2bOKIiwoNQOgs8GAuAlFcXn4JQyYa8fNuCLO99/jcsE+PWVVoAx?= =?us-ascii?Q?7INL19bNqjYiuRj8v8jQhgq/c8tM9l6cJIqxpQspLsCbgeEEJlP8lfoqhqYj?= =?us-ascii?Q?SvMGcqZlvZYlfBHebkVK0t8LoPDSQMqygfAa+SFSv+qfQWkxJsV49hrDBUHQ?= =?us-ascii?Q?NNWRewNmW6+SfQnpBlLSaEihvUL5dmCbpWiqrBlj6Min+eNvF/vgwYeEnock?= =?us-ascii?Q?/3OFonL31hw1mjpGCS29JhLgbeonruuJNeahD2j0264w3rX8kZ/LLQ=3D=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:SATLEXMB03.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(36860700013)(1800799024)(376014)(7416014)(82310400026)(921020);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Sep 2024 11:13:35.9391 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a5a8c265-feb4-4eb7-d231-08dcccd29edb X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB03.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B070.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR12MB6059 Content-Type: text/plain; charset="utf-8" On PREEMPT_RT kernels, softirq_ctrl.cnt tracks the softirq count and set the task::softirqs_disabled_cnt accordingly. This count is always 'changed by SOFTIRQ_OFFSET when entering and leaving softirq processing' or 'SOFTIRQ_DISABLE_OFFSET (=3D 2 * SOFTIRQ_OFFSET) on local_bh_disable or local_bh_enable", as stated in the comment about softirq_ctrl declaration. Soon, the softirq_ctrl.cnt will also be used by !PREEMPT_RT kernels to track an impending call to do_softirq() in order to prevent pointless wakeup of ksoftirqd which will use the lower bits of softirq_ctrl.cnt. Mask all the current reads of softirq_ctrl.cnt on PREEMPT_RT kernels with SOFTIRQ_MASK to track only multiples of SOFTIRQ_OFFSET based changes. No functional change intended. Signed-off-by: K Prateek Nayak --- v1..v2: - New patch. Broken off from approach discussed in https://lore.kernel.org/lkml/880f13fd-753d-2c5a-488a-d75c99e8dfa3@amd.com/ --- kernel/softirq.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 8c4524ce65fa..e70a51d737ee 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -138,7 +138,7 @@ static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl= ) =3D { */ bool local_bh_blocked(void) { - return __this_cpu_read(softirq_ctrl.cnt) !=3D 0; + return (__this_cpu_read(softirq_ctrl.cnt) & SOFTIRQ_MASK) !=3D 0; } =20 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt) @@ -155,7 +155,8 @@ void __local_bh_disable_ip(unsigned long ip, unsigned i= nt cnt) /* Required to meet the RCU bottomhalf requirements. */ rcu_read_lock(); } else { - DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt)); + DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt) & + SOFTIRQ_MASK); } } =20 @@ -163,7 +164,7 @@ void __local_bh_disable_ip(unsigned long ip, unsigned i= nt cnt) * Track the per CPU softirq disabled state. On RT this is per CPU * state to allow preemption of bottom half disabled sections. */ - newcnt =3D __this_cpu_add_return(softirq_ctrl.cnt, cnt); + newcnt =3D __this_cpu_add_return(softirq_ctrl.cnt, cnt) & SOFTIRQ_MASK; /* * Reflect the result in the task state to prevent recursion on the * local lock and to make softirq_count() & al work. @@ -184,7 +185,7 @@ static void __local_bh_enable(unsigned int cnt, bool un= lock) int newcnt; =20 DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=3D - this_cpu_read(softirq_ctrl.cnt)); + (this_cpu_read(softirq_ctrl.cnt) & SOFTIRQ_MASK)); =20 if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() =3D=3D cnt) { raw_local_irq_save(flags); @@ -192,7 +193,7 @@ static void __local_bh_enable(unsigned int cnt, bool un= lock) raw_local_irq_restore(flags); } =20 - newcnt =3D __this_cpu_sub_return(softirq_ctrl.cnt, cnt); + newcnt =3D __this_cpu_sub_return(softirq_ctrl.cnt, cnt) & SOFTIRQ_MASK; current->softirq_disable_cnt =3D newcnt; =20 if (!newcnt && unlock) { @@ -212,7 +213,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned in= t cnt) lockdep_assert_irqs_enabled(); =20 local_irq_save(flags); - curcnt =3D __this_cpu_read(softirq_ctrl.cnt); + curcnt =3D __this_cpu_read(softirq_ctrl.cnt) & SOFTIRQ_MASK; =20 /* * If this is not reenabling soft interrupts, no point in trying to --=20 2.34.1