[PATCH] powerpc/64s: Fix irq tracing corruption in interrupt/syscall return caused by perf interrupts

[Alexey Kardashevskiy]

On 22/07/2020 17:34, Nicholas Piggin wrote:
> Alexey reports lockdep_assert_irqs_enabled() warnings when stress testing perf, e.g.,
> 
> WARNING: CPU: 0 PID: 1556 at kernel/softirq.c:169 __local_bh_enable_ip+0x258/0x270
> CPU: 0 PID: 1556 Comm: syz-executor
> NIP:  c0000000001ec888 LR: c0000000001ec884 CTR: c000000000ef0610
> REGS: c000000022d4f8a0 TRAP: 0700   Not tainted  (5.8.0-rc3-x)
> MSR:  8000000000029033 <SF,EE,ME,IR,DR,RI,LE>  CR: 28008844  XER: 20040000
> CFAR: c0000000001dc1d0 IRQMASK: 0
> 
> The interesting thing is MSR[EE] and IRQMASK shows interrupts are enabled,
> suggesting the current->hardirqs_enabled irq tracing state is going out of sync
> with the actual interrupt enable state.
> 
> The cause is a window in interrupt/syscall return where irq tracing state is being
> adjusted for an irqs-enabled return while MSR[EE] is still enabled. A perf
> interrupt hits and ends up calling trace_hardirqs_off() when restoring
> interrupt flags to a disable state.
> 
> Fix this by disabling perf interrupts as well while adjusting irq tracing state.
> 
> Add a debug check that catches the condition sooner.
> 
> Fixes: 68b34588e202 ("powerpc/64/sycall: Implement syscall entry/exit logic in C")
> Reported-by: Alexey Kardashevskiy <aik at ozlabs.ru>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> 
> I can reproduce similar symptoms and this patch fixes my test case,
> still trying to confirm Alexey's test case or whether there's another
> similar bug causing it.


This does not fix my testcase. I applied this on top of 4fa640dc5230
("Merge tag 'vfio-v5.8-rc7' of git://github.com/awilliam/linux-vfio into
master")  without any of my testing code, just to be clear. Sorry...


> 
>  arch/powerpc/kernel/syscall_64.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/syscall_64.c b/arch/powerpc/kernel/syscall_64.c
> index 79edba3ab312..6c6f88eff915 100644
> --- a/arch/powerpc/kernel/syscall_64.c
> +++ b/arch/powerpc/kernel/syscall_64.c
> @@ -107,8 +107,13 @@ notrace long system_call_exception(long r3, long r4, long r5,
>   */
>  static notrace inline bool prep_irq_for_enabled_exit(void)
>  {
> -	/* This must be done with RI=1 because tracing may touch vmaps */
> -	trace_hardirqs_on();
> +	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS)) {
> +		/* Prevent perf interrupts hitting and messing up the trace_hardirqs state */
> +		irq_soft_mask_set(IRQS_ALL_DISABLED);
> +
> +		/* This must be done with RI=1 because tracing may touch vmaps */
> +		trace_hardirqs_on();
> +	}
>  
>  	/* This pattern matches prep_irq_for_idle */
>  	__hard_EE_RI_disable();
> @@ -123,6 +128,8 @@ static notrace inline bool prep_irq_for_enabled_exit(void)
>  	local_paca->irq_happened = 0;
>  	irq_soft_mask_set(IRQS_ENABLED);
>  
> +	lockdep_assert_irqs_enabled();
> +
>  	return true;
>  }
>  
> 

-- 
Alexey