Srivatsa S. Bhat
2022-May-13 23:32 UTC
[PATCH v3] arm64: paravirt: Use RCU read locks to guard stolen_time
On 5/13/22 10:46 AM, Elliot Berman wrote:> From: Prakruthi Deepak Heragu <quic_pheragu at quicinc.com> > > 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 at kernel.org> > Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu at quicinc.com> > Signed-off-by: Elliot Berman <quic_eberman at quicinc.com> > ---Looks good to me, but one quick question though (see below). Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa at csail.mit.edu>> > 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? Regards, Srivatsa
Will Deacon
2022-May-17 08:54 UTC
[PATCH v3] arm64: paravirt: Use RCU read locks to guard stolen_time
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 at quicinc.com> > > > > 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 at kernel.org> > > Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu at quicinc.com> > > Signed-off-by: Elliot Berman <quic_eberman at quicinc.com> > > --- > > Looks good to me, but one quick question though (see below). > > Reviewed-by: Srivatsa S. Bhat (VMware) <srivatsa at csail.mit.edu>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