Thread (7 messages) flat view 7 messages, 3 authors, 6d ago

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

From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2026-09-08 18:08:42
Also in: linux-mediatek, linux-usb, lkml
Subsystem: mediatek usb3 drd ip driver, the rest, usb subsystem · Maintainers: Chunfeng Yun, Linus Torvalds, Greg Kroah-Hartman 

On Mon, Sep 07, 2026 at 02:28:47PM +0100, Vladimir Murzin wrote:
On 9/4/26 00:59, Paul E. McKenney wrote:
quoted
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 :)
quoted
[    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 [off-list ref]
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 [off-list ref]
    Cc: Chunfeng Yun [off-list ref]
    Cc: Greg Kroah-Hartman [off-list ref]
    Cc: [off-list ref]
    Cc: [off-list ref]
    Cc: [off-list ref]

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',
Other recent patches touching these files
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help