From: "tip-bot2 for Reinette Chatre" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: James Morse <james.morse@arm.com>,
Reinette Chatre <reinette.chatre@intel.com>,
Borislav Petkov <bp@suse.de>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: x86/cache] x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI
Date: Mon, 11 Jan 2021 10:50:09 -0000 [thread overview]
Message-ID: <161036220932.414.7291518717313407438.tip-bot2@tip-bot2> (raw)
In-Reply-To: =?utf-8?q?=3Ce9e68ce1441a73401e08b641cc3b9a3cf13fe6d4=2E16082?= =?utf-8?q?43147=2Egit=2Ereinette=2Echatre=40intel=2Ecom=3E?=
The following commit has been merged into the x86/cache branch of tip:
Commit-ID: e0ad6dc8969f790f14bddcfd7ea284b7e5f88a16
Gitweb: https://git.kernel.org/tip/e0ad6dc8969f790f14bddcfd7ea284b7e5f88a16
Author: Reinette Chatre <reinette.chatre@intel.com>
AuthorDate: Thu, 17 Dec 2020 14:31:20 -08:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 11 Jan 2021 11:34:45 +01:00
x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI
James reported in [1] that there could be two tasks running on the same CPU
with task_struct->on_cpu set. Using task_struct->on_cpu as a test if a task
is running on a CPU may thus match the old task for a CPU while the
scheduler is running and IPI it unnecessarily.
task_curr() is the correct helper to use. While doing so move the #ifdef
check of the CONFIG_SMP symbol to be a C conditional used to determine
if this helper should be used to ensure the code is always checked for
correctness by the compiler.
[1] https://lore.kernel.org/lkml/a782d2f3-d2f6-795f-f4b1-9462205fd581@arm.com
Reported-by: James Morse <james.morse@arm.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/e9e68ce1441a73401e08b641cc3b9a3cf13fe6d4.1608243147.git.reinette.chatre@intel.com
---
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 460f3e0..37f37df 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -2313,19 +2313,15 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
t->closid = to->closid;
t->rmid = to->mon.rmid;
-#ifdef CONFIG_SMP
/*
- * This is safe on x86 w/o barriers as the ordering
- * of writing to task_cpu() and t->on_cpu is
- * reverse to the reading here. The detection is
- * inaccurate as tasks might move or schedule
- * before the smp function call takes place. In
- * such a case the function call is pointless, but
+ * If the task is on a CPU, set the CPU in the mask.
+ * The detection is inaccurate as tasks might move or
+ * schedule before the smp function call takes place.
+ * In such a case the function call is pointless, but
* there is no other side effect.
*/
- if (mask && t->on_cpu)
+ if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t))
cpumask_set_cpu(task_cpu(t), mask);
-#endif
}
}
read_unlock(&tasklist_lock);
reply other threads:[~2021-01-11 10:50 UTC|newest]
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