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Re: [PATCH v2 3/3] xen/sched: fix cpu hotplug
- To: Juergen Gross <jgross@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 15 Aug 2022 14:27:07 +0200
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- Cc: George Dunlap <george.dunlap@xxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Gao Ruifeng <ruifeng.gao@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 15 Aug 2022 12:27:19 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 15.08.2022 13:04, Juergen Gross wrote:
> Cpu cpu unplugging is calling schedule_cpu_rm() via stop_machine_run()
> with interrupts disabled, thus any memory allocation or freeing must
> be avoided.
>
> Since commit 5047cd1d5dea ("xen/common: Use enhanced
> ASSERT_ALLOC_CONTEXT in xmalloc()") this restriction is being enforced
> via an assertion, which will now fail.
>
> Before that commit cpu unplugging in normal configurations was working
> just by chance as only the cpu performing schedule_cpu_rm() was doing
> active work. With core scheduling enabled, however, failures could
> result from memory allocations not being properly propagated to other
> cpus' TLBs.
>
> Fix this mess by allocating needed memory before entering
> stop_machine_run() and freeing any memory only after having finished
> stop_machine_run().
>
> Fixes: 1ec410112cdd ("xen/sched: support differing granularity in
> schedule_cpu_[add/rm]()")
> Reported-by: Gao Ruifeng <ruifeng.gao@xxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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