On Fri, May 13, 2022 at 04:32:53PM -0700, Srivatsa S. Bhat wrote:
> On 5/13/22 10:46 AM, Elliot Berman wrote:
> > From: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
> >
> > During hotplug, the stolen time data structure is unmapped and memset.
> > There is a possibility of the timer IRQ being triggered before memset
> > and stolen time is getting updated as part of this timer IRQ handler. This
> > causes the below crash in timer handler -
> >
> > [ 3457.473139][ C5] Unable to handle kernel paging request at virtual address ffffffc03df05148
> > ...
> > [ 3458.154398][ C5] Call trace:
> > [ 3458.157648][ C5] para_steal_clock+0x30/0x50
> > [ 3458.162319][ C5] irqtime_account_process_tick+0x30/0x194
> > [ 3458.168148][ C5] account_process_tick+0x3c/0x280
> > [ 3458.173274][ C5] update_process_times+0x5c/0xf4
> > [ 3458.178311][ C5] tick_sched_timer+0x180/0x384
> > [ 3458.183164][ C5] __run_hrtimer+0x160/0x57c
> > [ 3458.187744][ C5] hrtimer_interrupt+0x258/0x684
> > [ 3458.192698][ C5] arch_timer_handler_virt+0x5c/0xa0
> > [ 3458.198002][ C5] handle_percpu_devid_irq+0xdc/0x414
> > [ 3458.203385][ C5] handle_domain_irq+0xa8/0x168
> > [ 3458.208241][ C5] gic_handle_irq.34493+0x54/0x244
> > [ 3458.213359][ C5] call_on_irq_stack+0x40/0x70
> > [ 3458.218125][ C5] do_interrupt_handler+0x60/0x9c
> > [ 3458.223156][ C5] el1_interrupt+0x34/0x64
> > [ 3458.227560][ C5] el1h_64_irq_handler+0x1c/0x2c
> > [ 3458.232503][ C5] el1h_64_irq+0x7c/0x80
> > [ 3458.236736][ C5] free_vmap_area_noflush+0x108/0x39c
> > [ 3458.242126][ C5] remove_vm_area+0xbc/0x118
> > [ 3458.246714][ C5] vm_remove_mappings+0x48/0x2a4
> > [ 3458.251656][ C5] __vunmap+0x154/0x278
> > [ 3458.255796][ C5] stolen_time_cpu_down_prepare+0xc0/0xd8
> > [ 3458.261542][ C5] cpuhp_invoke_callback+0x248/0xc34
> > [ 3458.266842][ C5] cpuhp_thread_fun+0x1c4/0x248
> > [ 3458.271696][ C5] smpboot_thread_fn+0x1b0/0x400
> > [ 3458.276638][ C5] kthread+0x17c/0x1e0
> > [ 3458.280691][ C5] ret_from_fork+0x10/0x20
> >
> > As a fix, introduce rcu lock to update stolen time structure.
> >
> > Suggested-by: Will Deacon <will@xxxxxxxxxx>
> > Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
> > Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
> > ---
>
> Looks good to me, but one quick question though (see below).
>
> Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa@xxxxxxxxxxxxx>
Cheers.
> > static int stolen_time_cpu_down_prepare(unsigned int cpu)
> > {
> > + struct pvclock_vcpu_stolen_time *kaddr = NULL;
> > struct pv_time_stolen_time_region *reg;
> >
> > reg = this_cpu_ptr(&stolen_time_region);
> > if (!reg->kaddr)
> > return 0;
> >
> > - memunmap(reg->kaddr);
> > - memset(reg, 0, sizeof(*reg));
> > + kaddr = rcu_replace_pointer(reg->kaddr, NULL, true);
> > + synchronize_rcu();
> > + memunmap(kaddr);
> >
>
> The original code used to memset the stolen time region, but this
> patch seems to drop it. Was that change intentional?
'struct pv_time_stolen_time_region' only has one field ('kaddr'), which
we're now clearing with rcu_replace_pointer() so the memset doesn't make
sense.
Will
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