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From: Phil Auld <pauld@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arch/arm64:  Fix topology initialization for core scheduling
Date: Tue, 22 Mar 2022 12:03:04 -0400	[thread overview]
Message-ID: <20220322160304.26229-1-pauld@redhat.com> (raw)

Some arm64 rely on store_cpu_topology() to setup the real topology.
This needs to be done before the call to notify_cpu_starting() which
tell the scheduler about the cpu otherwise the core scheduling data
structures are setup in a way that does not match the actual topology.

Without this change stress-ng (which enables core scheduling in its prctl 
tests) causes a warning and then a crash (trimmed for legibility):

[ 1853.805168] ------------[ cut here ]------------
[ 1853.809784] task_rq(b)->core != rq->core
[ 1853.809792] WARNING: CPU: 117 PID: 0 at kernel/sched/fair.c:11102 cfs_prio_less+0x1b4/0x1c4
...
[ 1854.015210] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
...
[ 1854.231256] Call trace:
[ 1854.233689]  pick_next_task+0x3dc/0x81c
[ 1854.237512]  __schedule+0x10c/0x4cc
[ 1854.240988]  schedule_idle+0x34/0x54

Fixes: 9edeaea1bc45 ("sched: Core-wide rq->lock")
Signed-off-by: Phil Auld <pauld@redhat.com>
---
This is a similar issue to 
  f2703def339c ("MIPS: smp: fill in sibling and core maps earlier") 
which fixed it for MIPS. 



 arch/arm64/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 27df5c1e6baa..3b46041f2b97 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -234,6 +234,7 @@ asmlinkage notrace void secondary_start_kernel(void)
 	 * Log the CPU info before it is marked online and might get read.
 	 */
 	cpuinfo_store_cpu();
+	store_cpu_topology(cpu);
 
 	/*
 	 * Enable GIC and timers.
@@ -242,7 +243,6 @@ asmlinkage notrace void secondary_start_kernel(void)
 
 	ipi_setup(cpu);
 
-	store_cpu_topology(cpu);
 	numa_add_cpu(cpu);
 
 	/*
-- 
2.18.0


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             reply	other threads:[~2022-03-22 16:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-22 16:03 Phil Auld [this message]
2022-03-29 14:02 ` [PATCH] arch/arm64: Fix topology initialization for core scheduling Dietmar Eggemann
2022-03-29 15:20   ` Phil Auld
2022-03-29 18:55     ` Dietmar Eggemann
2022-03-29 19:50       ` Phil Auld
2022-03-30 15:48         ` Dietmar Eggemann
2022-03-30 15:52           ` Phil Auld
2022-03-30 16:07           ` Phil Auld

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