Messages in this thread | | | Date | Thu, 31 Mar 2022 11:04:31 +0200 | Subject | Re: [PATCH v2] arch/arm64: Fix topology initialization for core scheduling | From | Dietmar Eggemann <> |
| |
On 30/03/2022 17:56, Phil Auld wrote: > Arm64 systems rely on store_cpu_topology() to call update_siblings_masks() > to transfer the toplogy to the various cpu masks. This needs to be done > before the call to notify_cpu_starting() which tells the scheduler about > each cpu found, 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. > > v2: Fixed the commit message. No code change.
Ah, the reason is that smt_mask is not correctly setup, so we bail on `cpumask_weight(smt_mask) == 1` for !leaders in:
notify_cpu_starting() cpuhp_invoke_callback_range() sched_cpu_starting() sched_core_cpu_starting()
which leads to rq->core not being correctly set for !leader-rq's.
LGTM. Tested on: HPE Apollo 70 X1
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
[...]
| |