Re: [PATCH] perf: arm_pmu_acpi: Fix armpmu_alloc call from invalid context

[Mark Salter]

On Thu, 2018-02-08 at 17:54 +0000, Mark Rutland wrote:
> Hi Mark,
> 
> On Thu, Feb 08, 2018 at 12:45:04PM -0500, Mark Salter wrote:
> > When booting an arm64 debug kernel with ACPI, I see:
> > 
> >    BUG: sleeping function called from invalid context at mm/slab.h:420
> >    in_atomic(): 0, irqs_disabled(): 128, pid: 12, name: cpuhp/0
> >    1 lock held by cpuhp/0/12:
> >     #0:  (cpuhp_state-up){+.+.}, at: [<0000000057aa0dae>] cpuhp_thread_fun+0x13c/0x258
> >    irq event stamp: 28
> >    hardirqs last  enabled at (27): [<000000000b861658>] _raw_spin_unlock_irq+0x38/0x58
> >    hardirqs last disabled at (28): [<000000006231cfb1>] cpuhp_thread_fun+0xd0/0x258
> >    softirqs last  enabled at (0): [<0000000054d9737a>] copy_process.isra.32.part.33+0x450/0x1480
> >    softirqs last disabled at (0): [<          (null)>]           (null)
> >    CPU: 0 PID: 12 Comm: cpuhp/0 Not tainted 4.15.0+ #18
> >    Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board, BIOS 3.06.25 Oct 17 2016
> >    Call trace:
> >     dump_backtrace+0x0/0x188
> >     show_stack+0x24/0x2c
> >     dump_stack+0xa4/0xe0
> >     ___might_sleep+0x208/0x234
> >     __might_sleep+0x58/0x8c
> >     kmem_cache_alloc_trace+0x248/0x3e0
> >     armpmu_alloc+0x38/0x1a8
> >     arm_pmu_acpi_cpu_starting+0x11c/0x15c
> >     cpuhp_invoke_callback+0x120/0x100c
> >     cpuhp_thread_fun+0xe8/0x258
> >     smpboot_thread_fn+0x170/0x268
> >     kthread+0x110/0x13c
> >     ret_from_fork+0x10/0x18
> 
> I have patches to address this:
> 
> http://lists.infradead.org/pipermail/linux-arm-kernel/2018-February/557838.html
> https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/acpi-pmu-lockdep

Awesome, I completely missed that. Thanks.

> 
> > With commit 7d88eb695a1f ("arm/perf: Convert to hotplug state machine"),
> > arm_pmu uses the cpuhotplug framework to initialize the PMU driver when
> > using ACPI. However, the arm_pmu_acpi_cpu_starting() callback comes
> > before CPUHP_AP_ONLINE is reached which means it runs with interrupts
> > diabled and tries to allocate memory with GFP_KERNEL alloc which may
> > sleep.
> > 
> > Move CPUHP_AP_PERF_ARM_ACPI_STARTING to come after CPUHP_AP_ONLINE so
> > that the arm_pmu initialization runs with interrupts enabled as it
> > does when booting with device tree.
> > 
> > Fixes: 7d88eb695a1f ("arm/perf: Convert to hotplug state machine")
> > Signed-off-by: Mark Salter <msalter@xxxxxxxxxx>
> > ---
> >  include/linux/cpuhotplug.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> > index 5172ad0..e07b2da 100644
> > --- a/include/linux/cpuhotplug.h
> > +++ b/include/linux/cpuhotplug.h
> > @@ -114,7 +114,6 @@ enum cpuhp_state {
> >  	CPUHP_AP_ARM_VFP_STARTING,
> >  	CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
> >  	CPUHP_AP_PERF_ARM_HW_BREAKPOINT_STARTING,
> > -	CPUHP_AP_PERF_ARM_ACPI_STARTING,
> >  	CPUHP_AP_PERF_ARM_STARTING,
> >  	CPUHP_AP_ARM_L2X0_STARTING,
> >  	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
> > @@ -146,6 +145,7 @@ enum cpuhp_state {
> >  	CPUHP_AP_SMPBOOT_THREADS,
> >  	CPUHP_AP_X86_VDSO_VMA_ONLINE,
> >  	CPUHP_AP_IRQ_AFFINITY_ONLINE,
> > +	CPUHP_AP_PERF_ARM_ACPI_STARTING,
> 
> We need CPUHP_AP_PERF_ARM_ACPI_STARTING to happen before
> CPUHP_AP_PERF_ARM_STARTING, and I think this re-ordering prevents us
> from correctly resetting the PMU and enabling percpu interrupts, at
> least in heterogeneous configurations (e.g. big.LITTLE systems like
> Juno).
> 
> I'm not sure whether we could safely move both callbacks this late.
> 
> Thanks,
> Mark.