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SubjectRe: [v6] usb: ohci: Proper handling of ed_rm_list to handle race condition between usb_kill_urb() and finish_unlinks()
Hi,

On 25 March 2018 at 12:21, Jonathan Liu <net147@gmail.com> wrote:
> On 8 February 2018 at 14:55, Jeffy Chen <jeffy.chen@rock-chips.com> wrote:
>> From: AMAN DEEP <aman.deep@samsung.com>
>>
>> There is a race condition between finish_unlinks->finish_urb() function
>> and usb_kill_urb() in ohci controller case. The finish_urb calls
>> spin_unlock(&ohci->lock) before usb_hcd_giveback_urb() function call,
>> then if during this time, usb_kill_urb is called for another endpoint,
>> then new ed will be added to ed_rm_list at beginning for unlink, and
>> ed_rm_list will point to newly added.
>>
>> When finish_urb() is completed in finish_unlinks() and ed->td_list
>> becomes empty as in below code (in finish_unlinks() function):
>>
>> if (list_empty(&ed->td_list)) {
>> *last = ed->ed_next;
>> ed->ed_next = NULL;
>> } else if (ohci->rh_state == OHCI_RH_RUNNING) {
>> *last = ed->ed_next;
>> ed->ed_next = NULL;
>> ed_schedule(ohci, ed);
>> }
>>
>> The *last = ed->ed_next will make ed_rm_list to point to ed->ed_next
>> and previously added ed by usb_kill_urb will be left unreferenced by
>> ed_rm_list. This causes usb_kill_urb() hang forever waiting for
>> finish_unlink to remove added ed from ed_rm_list.
>>
>> The main reason for hang in this race condtion is addition and removal
>> of ed from ed_rm_list in the beginning during usb_kill_urb and later
>> last* is modified in finish_unlinks().
>>
>> As suggested by Alan Stern, the solution for proper handling of
>> ohci->ed_rm_list is to remove ed from the ed_rm_list before finishing
>> any URBs. Then at the end, we can add ed back to the list if necessary.
>>
>> This properly handle the updated ohci->ed_rm_list in usb_kill_urb().
>>
>> Fixes:977dcfdc6031("USB:OHCI:don't lose track of EDs when a controller dies")
>> Acked-by: Alan Stern <stern@rowland.harvard.edu>
>> CC: <stable@vger.kernel.org>
>> Signed-off-by: Aman Deep <aman.deep@samsung.com>
>> Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
>> ---
>>
>> Changes in v6:
>> This is a resend of Aman Deep's v5 patch [0], which solved the hang we
>> hit [1]. (Thanks Aman :)
>>
>> The v5 has some format issues, so i slightly adjust the commit message.
>>
>> [0] https://www.spinics.net/lists/linux-usb/msg129010.html
>> [1] https://bugs.chromium.org/p/chromium/issues/detail?id=803749
>>
>> drivers/usb/host/ohci-q.c | 17 ++++++++++-------
>> 1 file changed, 10 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/usb/host/ohci-q.c b/drivers/usb/host/ohci-q.c
>> index b2ec8c399363..4ccb85a67bb3 100644
>> --- a/drivers/usb/host/ohci-q.c
>> +++ b/drivers/usb/host/ohci-q.c
>> @@ -1019,6 +1019,8 @@ static void finish_unlinks(struct ohci_hcd *ohci)
>> * have modified this list. normally it's just prepending
>> * entries (which we'd ignore), but paranoia won't hurt.
>> */
>> + *last = ed->ed_next;
>> + ed->ed_next = NULL;
>> modified = 0;
>>
>> /* unlink urbs as requested, but rescan the list after
>> @@ -1077,21 +1079,22 @@ static void finish_unlinks(struct ohci_hcd *ohci)
>> goto rescan_this;
>>
>> /*
>> - * If no TDs are queued, take ED off the ed_rm_list.
>> + * If no TDs are queued, ED is now idle.
>> * Otherwise, if the HC is running, reschedule.
>> - * If not, leave it on the list for further dequeues.
>> + * If the HC isn't running, add ED back to the
>> + * start of the list for later processing.
>> */
>> if (list_empty(&ed->td_list)) {
>> - *last = ed->ed_next;
>> - ed->ed_next = NULL;
>> ed->state = ED_IDLE;
>> list_del(&ed->in_use_list);
>> } else if (ohci->rh_state == OHCI_RH_RUNNING) {
>> - *last = ed->ed_next;
>> - ed->ed_next = NULL;
>> ed_schedule(ohci, ed);
>> } else {
>> - last = &ed->ed_next;
>> + ed->ed_next = ohci->ed_rm_list;
>> + ohci->ed_rm_list = ed;
>> + /* Don't loop on the same ED */
>> + if (last == &ohci->ed_rm_list)
>> + last = &ed->ed_next;
>> }
>>
>> if (modified)
>
> I am experiencing a USB function call hang from userspace with OCHI
> (full speed USB device) after updating from Linux 4.14.15 to 4.14.24
> and noticed this commit.
>
> Here is the Linux 4.14.24 kernel stack trace (extracted from SysRq+w
> and amended with addr2line):
> [<c05cbd64>] (__schedule) from [<c05cc148>] (schedule+0x50/0xb4)
> kernel/sched/core.c:2792
> [<c05cc148>] (schedule) from [<c042789c>]
> (usb_kill_urb.part.3+0x78/0xa8) include/asm-generic/preempt.h:59
> [<c042789c>] (usb_kill_urb.part.3) from [<c0433a3c>]
> (usbdev_ioctl+0x1288/0x1cf0) drivers/usb/core/urb.c:690
> [<c0433a3c>] (usbdev_ioctl) from [<c0217db8>]
> (do_vfs_ioctl+0x9c/0x8ec) drivers/usb/core/devio.c:1835
> [<c0217db8>] (do_vfs_ioctl) from [<c021863c>] (SyS_ioctl+0x34/0x5c)
> fs/ioctl.c:47
> [<c021863c>] (SyS_ioctl) from [<c0107820>] (ret_fast_syscall+0x0/0x54)
> include/linux/file.h:39
>
> Afterwards the kernel is unresponsive to disconnect/connect of the
> full speed USB device but I can connect/disconnect a high speed USB
> device to the same port and communicate to it without problem since it
> uses EHCI (OHCI is companion controller). If I try to connect the full
> speed USB device again it is still unresponsive. The userspace
> application is still hanging after all this.
>
> Could this commit be causing the issue?

There does seem to be something wrong with this commit. I did some
more testing with Linux 4.16.0-rc6 on sun7i-a20-olinuxino-lime.
I connected a sun7i-a20-pcduino3b running Linux 4.15.12 that has OTG
port with gadget zero kernel module (g_zero) loaded to the USB port
and did some testing with usbtest from tools/usb/testusb.c in kernel
repository.

I had to do the following change to avoid getting flooded with
"usbtest 1-1:3.0: unlink retry" kernel messages after test 11 of
testusb starts:
--- a/drivers/usb/misc/usbtest.c
+++ b/drivers/usb/misc/usbtest.c
@@ -1473,7 +1473,7 @@ static int unlink1(struct usbtest_dev *dev, int
pipe, int
size, int async)
* resubmission, but since we're testing unlink
* paths, we can't.
*/
- ERROR(dev, "unlink retry\n");
+ /*ERROR(dev, "unlink retry\n");*/
continue;
case 0:
case -EINPROGRESS:
Here are the results.

# ./testusb -a
/dev/bus/usb/001/002 test 0, 0.006822 secs
/dev/bus/usb/001/002 test 1, 0.140112 secs
/dev/bus/usb/001/002 test 2, 0.381125 secs
/dev/bus/usb/001/002 test 3, 0.133564 secs
/dev/bus/usb/001/002 test 4, 0.385498 secs
/dev/bus/usb/001/002 test 5, 2.138259 secs
/dev/bus/usb/001/002 test 6, 1.755144 secs
/dev/bus/usb/001/002 test 7, 2.137387 secs
/dev/bus/usb/001/002 test 8, 1.752393 secs
/dev/bus/usb/001/002 test 9, 1.132559 secs
/dev/bus/usb/001/002 test 10, 3.698934 secs
/dev/bus/usb/001/002 test 11, 40.061114 secs

dmesg (processed through scripts/decode_stacktrace.sh from kernel repository):
[ 21.573242] usbtest 1-1:3.0: TEST 0: NOP
[ 21.580315] usbtest 1-1:3.0: TEST 1: write 1024 bytes 1000 times
[ 21.732138] usbtest 1-1:3.0: TEST 2: read 1024 bytes 1000 times
[ 22.132133] usbtest 1-1:3.0: TEST 3: write/1024 0..1024 bytes 1000 times
[ 22.282137] usbtest 1-1:3.0: TEST 4: read/1024 0..1024 bytes 1000 times
[ 22.682131] usbtest 1-1:3.0: TEST 5: write 1000 sglists 32 entries
of 1024 bytes
[ 24.832138] usbtest 1-1:3.0: TEST 6: read 1000 sglists 32 entries
of 1024 bytes
[ 26.602135] usbtest 1-1:3.0: TEST 7: write/1024 1000 sglists 32
entries 0..1024 bytes
[ 28.752136] usbtest 1-1:3.0: TEST 8: read/1024 1000 sglists 32
entries 0..1024 bytes
[ 30.522139] usbtest 1-1:3.0: TEST 9: ch9 (subset) control tests, 1000 times
[ 31.654957] usbtest 1-1:3.0: TEST 10: queue 32 control calls, 1000 times
[ 35.354220] usbtest 1-1:3.0: TEST 11: unlink 1000 reads of 1024
[ 75.414099] usbtest 1-1:3.0: TEST 12: unlink 1000 writes of 1024
[ 128.026194] INFO: rcu_sched self-detected stall on CPU
[ 128.031367] 0-....: (1 GPs behind) idle=faa/1/1073741826
softirq=2614/2621 fqs=1048
[ 128.039182] (t=2100 jiffies g=227 c=226 q=1961)
[ 128.043887] NMI backtrace for cpu 0
[ 128.047377] CPU: 0 PID: 262 Comm: testusb Tainted: G O
4.16.0-rc6 #1
[ 128.054932] Hardware name: Allwinner sun7i (A20) Family
[ 128.060181] (unwind_backtrace) from show_stack (arch/arm/kernel/traps.c:249)
[ 128.067921] (show_stack) from dump_stack (lib/dump_stack.c:55)
[ 128.075142] (dump_stack) from nmi_cpu_backtrace (lib/nmi_backtrace.c:103)
[ 128.083141] (nmi_cpu_backtrace) from nmi_trigger_cpumask_backtrace
(lib/nmi_backtrace.c:62)
[ 128.092704] (nmi_trigger_cpumask_backtrace) from
rcu_dump_cpu_stacks (kernel/rcu/tree.c:1373 (discriminator 2))
[ 128.102351] (rcu_dump_cpu_stacks) from rcu_check_callbacks
(kernel/rcu/tree.c:1526 kernel/rcu/tree.c:1592 kernel/rcu/tree.c:3361
kernel/rcu/tree.c:3423 kernel/rcu/tree.c:2763)
[ 128.111304] (rcu_check_callbacks) from update_process_times
(arch/arm/include/asm/thread_info.h:91
include/asm-generic/preempt.h:11 kernel/time/timer.c:1638)
[ 128.120173] (update_process_times) from tick_sched_timer
(kernel/time/tick-sched.c:1199)
[ 128.128777] (tick_sched_timer) from __hrtimer_run_queues
(kernel/time/hrtimer.c:1349 kernel/time/hrtimer.c:1411)
[ 128.137553] (__hrtimer_run_queues) from hrtimer_interrupt
(kernel/time/hrtimer.c:1472)
[ 128.146331] (hrtimer_interrupt) from arch_timer_handler_phys
(drivers/clocksource/arm_arch_timer.c:589
drivers/clocksource/arm_arch_timer.c:606)
[ 128.155285] (arch_timer_handler_phys) from handle_percpu_devid_irq
(kernel/irq/chip.c:909)
[ 128.164843] (handle_percpu_devid_irq) from generic_handle_irq
(kernel/irq/irqdesc.c:607)
[ 128.173880] (generic_handle_irq) from __handle_domain_irq
(kernel/irq/irqdesc.c:646)
[ 128.182574] (__handle_domain_irq) from gic_handle_irq
(arch/arm/include/asm/io.h:118 drivers/irqchip/irq-gic.c:360)
[ 128.190920] (gic_handle_irq) from __irq_svc
(arch/arm/kernel/entry-armv.S:226)
[ 128.198382] Exception stack(0xcda1fc88 to 0xcda1fcd0)
[ 128.203431] fc80: c0a95bc8 a0060013 0000000a
0000aa75 cd83b480 a0060013
[ 128.211598] fca0: cf7ee000 ffffff98 00000001 00000000 00000400
cec2b800 00000009 cda1fcd8
[ 128.219763] fcc0: c045b328 c0622890 20060013 ffffffff
[ 128.224818] (__irq_svc) from _raw_spin_unlock_irqrestore
(kernel/locking/spinlock.c:185)
[ 128.233428] (_raw_spin_unlock_irqrestore) from usb_hcd_unlink_urb
(drivers/usb/core/hcd.c:1720)
[ 128.242816] (usb_hcd_unlink_urb) from unlink1
(drivers/usb/core/hcd.c:864 drivers/usb/core/hcd.c:1684)
[ 128.250555] (unlink1) from unlink_simple (drivers/usb/misc/usbtest.c:1510)
[ 128.257774] (unlink_simple) from usbtest_do_ioctl
(drivers/usb/misc/usbtest.c:2360)
[ 128.266033] (usbtest_do_ioctl) from usbtest_ioctl
(drivers/usb/misc/usbtest.c:2685)
[ 128.274206] (usbtest_ioctl) from usbdev_ioctl
(drivers/usb/core/devio.c:2175 drivers/usb/core/devio.c:2197
drivers/usb/core/devio.c:2511 drivers/usb/core/devio.c:2555)
[ 128.282200] (usbdev_ioctl) from do_vfs_ioctl (fs/ioctl.c:47 fs/ioctl.c:686)
[ 128.289854] (do_vfs_ioctl) from SyS_ioctl (include/linux/file.h:39
fs/ioctl.c:702 fs/ioctl.c:692)
[ 128.297159] (SyS_ioctl) from ret_fast_syscall
(arch/arm/kernel/entry-common.S:52)
[ 128.304716] Exception stack(0xcda1ffa8 to 0xcda1fff0)
[ 128.309763] ffa0: 000119c4 00000000 00000003
c00c5512 bebbfb34 bebbfb34
[ 128.317931] ffc0: 000119c4 00000000 000109b0 00000036 00000000
00000000 b6fb0fac bebbfb44
[ 128.326096] ffe0: 00022034 bebbfb1c 00011020 b6ee073c
If I revert the commit, I can run "./testusb -a" to completion without
any issues with Linux 4.16.0-rc6 on sun7i-a20-olinuxino-lime.
I don't get a kernel stall detected when testing on x86_64 but I do
still get at least one "unlink retry" error message from kernel in
dmesg which can be reproduced using "./testusb -a" or more frequently
with "./testusb -a -t 11 -c 5000".

Regards,
Jonathan

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