[BUG/PATCH] drivers/usb/mtu3: Work around mtu3_log_ep double-indirection issue
Paul E. McKenney
paulmck at kernel.org
Tue Sep 8 11:08:33 PDT 2026
On Mon, Sep 07, 2026 at 02:28:47PM +0100, Vladimir Murzin wrote:
> 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
Does this less hacky patch do the trick?
Thanx, Paul
------------------------------------------------------------------------
commit afda2321e6e93a5bcc28bfb4717fbc3a1768446c
Author: Paul E. McKenney <paulmck at kernel.org>
Date: Thu Sep 3 16:48:09 2026 -0700
EXP drivers/usb/mtu3: Work around mtu3_log_ep double-indirection issue
Kernels built with either KASAN or KCSAN produce this splat:
[ 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
Therefore, work around this restriction by creating another entry in
TP_STRUCT__entry(), and do the double-indirection TP_fast_assign()
instead of TP_printk().
Signed-off-by: Paul E. McKenney <paulmck at kernel.org>
Cc: Chunfeng Yun <chunfeng.yun at mediatek.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: <linux-usb at vger.kernel.org>
Cc: <linux-arm-kernel at lists.infradead.org>
Cc: <linux-mediatek at lists.infradead.org>
diff --git a/drivers/usb/mtu3/mtu3_trace.h b/drivers/usb/mtu3/mtu3_trace.h
index 89870175d63561..6477ad3ddc66f6 100644
--- a/drivers/usb/mtu3/mtu3_trace.h
+++ b/drivers/usb/mtu3/mtu3_trace.h
@@ -224,6 +224,7 @@ DECLARE_EVENT_CLASS(mtu3_log_ep,
__field(unsigned int, flags)
__field(unsigned int, direction)
__field(struct mtu3_gpd_ring *, gpd_ring)
+ __field(dma_addr_t *, gpd_ring_dma)
),
TP_fast_assign(
__assign_str(name);
@@ -235,12 +236,13 @@ DECLARE_EVENT_CLASS(mtu3_log_ep,
__entry->flags = mep->flags;
__entry->direction = mep->is_in;
__entry->gpd_ring = &mep->gpd_ring;
+ __entry->gpd_ring_dma = &mep->gpd_ring->dma;
),
TP_printk("%s: type %s maxp %d slot %d mult %d burst %d ring %p/%pad 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->gpd_ring_dma,
__entry->flags & MTU3_EP_ENABLED ? 'E' : 'e',
__entry->flags & MTU3_EP_STALL ? 'S' : 's',
__entry->flags & MTU3_EP_WEDGE ? 'W' : 'w',
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