Re: [BUG/PATCH] drivers/usb/mtu3: Work around mtu3_log_ep double-indirection issue

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 9/4/26 00:59, Paul E. McKenney wrote:
> This is more bug report than patch, but this patch does suppress the
> splat, so there is that.  ;-)
> 
> Kernels built with either KASAN or KCSAN produce this splat:
> 

I see it on kernel w/o KASAN or KCSAN. IIUC, this is new check introduced
by b5cc230af5e5 ("tracing: Warn when an event dereferences a pointer in TP_printk()")
so adding Steven :)

> [    0.000000] TRACE EVENT ERROR: Event mtu3_gadget_ep_set_halt has double dereference in TP_printk: &REC->gpd_ring->dma
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] Event mtu3_gadget_ep_set_halt has double dereference in TP_printk: &REC->gpd_ring->dma
> [    0.000000] WARNING: kernel/trace/trace_events.c:420 at test_double_dereference+0x144/0x14c, CPU#0: swapper/0/0
> [    0.000000] Modules linked in:
> [    0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.3.0-rc1 #15247 PREEMPT
> [    0.000000] Hardware name: linux,dummy-virt (DT)
> [    0.000000] pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [    0.000000] pc : test_double_dereference+0x144/0x14c
> [    0.000000] lr : test_double_dereference+0x144/0x14c
> [    0.000000] sp : ffffc80aa7633bf0
> [    0.000000] x29: ffffc80aa7633bf0 x28: ffffc80aa7c0f047 x27: 000508b58019388f
> [    0.000000] x26: 0000000000000003 x25: 0000000000000007 x24: ffffc80aa5fceff8
> [    0.000000] x23: ffffc80aa7c0f05a x22: ffffc80aa64edfe8 x21: ffffc80aa7c0fce8
> [    0.000000] x20: ffffc80aa7c0f047 x19: 0000000000000013 x18: 0000000000000001
> [    0.000000] x17: 6572656420656c62 x16: 756f642073616820 x15: 746c61685f746573
> [    0.000000] x14: 0000000000000000 x13: ffff000139d90000 x12: 0000000000000045
> [    0.000000] x11: 00000000000000cf x10: ffff00013f546428 x9 : ffff000139d90000
> [    0.000000] x8 : 3fffffffffffc000 x7 : 0000000000000001 x6 : 0000000000000001
> [    0.000000] x5 : ffff00013f4e6440 x4 : 0000000000000000 x3 : 0000000000000000
> [    0.000000] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffffc80aa764a700
> [    0.000000] Call trace:
> [    0.000000]  test_double_dereference+0x144/0x14c (P)
> [    0.000000]  trace_event_raw_init+0x37c/0x5d8
> [    0.000000]  event_init+0x34/0xc0
> [    0.000000]  trace_event_init+0xec/0x588
> [    0.000000]  trace_init+0x24/0x6e0
> [    0.000000]  start_kernel+0x4a0/0x8ec
> [    0.000000]  __primary_switched+0x88/0x90
> [    0.000000] irq event stamp: 0
> [    0.000000] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [    0.000000] hardirqs last disabled at (0): [<0000000000000000>] 0x0
> [    0.000000] softirqs last  enabled at (0): [<0000000000000000>] 0x0
> [    0.000000] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [    0.000000] ---[ end trace 0000000000000000 ]---
> [    0.000000] TRACE EVENT ERROR: Event mtu3_gadget_ep_disable has double dereference in TP_printk: &REC->gpd_ring->dma
> [    0.000000] TRACE EVENT ERROR: Event mtu3_gadget_ep_enable has double dereference in TP_printk: &REC->gpd_ring->dma
> 
> Apparently, the code should instead create another entry in
> TP_STRUCT__entry(), and do the double-indirection TP_fast_assign() instead
> of TP_printk().  But simply removing the offending double indirection
> in TP_printk() gets this splat out of the way of other debugging.
> 

Indeed, splat has gone after applying the patch.

Thanks
Vladimir

> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: <linux-usb@vger.kernel.org>
> Cc: <linux-arm-kernel@lists.infradead.org>
> Cc: <linux-mediatek@lists.infradead.org>
> 
> diff --git a/drivers/usb/mtu3/mtu3_trace.h b/drivers/usb/mtu3/mtu3_trace.h
> index 89870175d63561..7c414e196d5871 100644
> --- a/drivers/usb/mtu3/mtu3_trace.h
> +++ b/drivers/usb/mtu3/mtu3_trace.h
> @@ -236,11 +236,11 @@ DECLARE_EVENT_CLASS(mtu3_log_ep,
>  		__entry->direction = mep->is_in;
>  		__entry->gpd_ring = &mep->gpd_ring;
>  	),
> -	TP_printk("%s: type %s maxp %d slot %d mult %d burst %d ring %p/%pad flags %c:%c%c%c:%c",
> +	TP_printk("%s: type %s maxp %d slot %d mult %d burst %d ring %p flags %c:%c%c%c:%c",
>  		__get_str(name), usb_ep_type_string(__entry->type),
>  		__entry->maxp, __entry->slot,
>  		__entry->mult, __entry->maxburst,
> -		__entry->gpd_ring, &__entry->gpd_ring->dma,
> +		__entry->gpd_ring,
>  		__entry->flags & MTU3_EP_ENABLED ? 'E' : 'e',
>  		__entry->flags & MTU3_EP_STALL ? 'S' : 's',
>  		__entry->flags & MTU3_EP_WEDGE ? 'W' : 'w',
>