Messages in this thread | | | Date | Mon, 5 Feb 2024 10:58:26 +0100 | Subject | Re: [PATCH][RFC] workqueue: Fix kernel panic on CPU hot-unplug | From | Helge Deller <> |
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Hi Tejun,
On 2/2/24 18:29, Tejun Heo wrote: > Hello, Helge. > > On Fri, Feb 02, 2024 at 09:41:38AM +0100, Helge Deller wrote: >> In a second step I extended your patch to print the present >> and online CPUs too. Below is the relevant dmesg part. >> >> Note, that on parisc the second CPU will be activated later in the >> boot process, after the kernel has the inventory. >> This I think differs vs x86, where all CPUs are available earlier >> in the boot process. >> ... >> [ 0.000000] XXX workqueue_init_early: possible_cpus=ffff present=0001 online=0001 > ... >> [ 0.228080] XXX workqueue_init: possible_cpus=ffff present=0001 online=0001 > ... >> [ 0.263466] XXX workqueue_init_topology: possible_cpus=ffff present=0001 online=0001 > > So, what's bothersome is that when the wq_dump.py script printing each cpu's > pwq, it's only printing for CPU 0 and 1. The for_each_possible_cpu() drgn > helper reads cpu_possible_mask from the kernel and iterates that, so that > most likely indicates at some point the cpu_possible_mask becomes 0x3 > instead of the one used during boot - 0xffff, which is problematic. > > Can you please sprinkle more printks to find out whether and when the > cpu_possible_mask changes during boot?
It seems the commit 0921244f6f4f ("parisc: Only list existing CPUs in cpu_possible_mask") is the culprit. Reverting that patch makes cpu hot-unplug work again. Furthermore this commit breaks the cpumask Kunit test as reported by Guenter: https://lkml.org/lkml/2024/2/4/146
So, I've added the revert to the parisc git tree and if my further tests go well I'll push it upstream.
Thanks for your help!! Helge
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