I suppose this is a regression?  If yes, which kernel it worked?
Also, kernel-debug would show the mutex deadlock more clearly.

Added Larry to Cc, who should have a better clue.

I have not run arm architecture, and I do not have any way to debug this here. The problem has not been reported on x86. Perhaps I should say yet, but there have been few changes in rtl8192cu or rtl_usb since 3.18. On the other hand, the wicked restarts have probably not been tested.

To help me, please run gdb on rtl_usb.ko from either the kernel source tree or /lib/modules. Then issue the command "l *_usb_read_sync+0xc4" and report the source code that is at fault. I think I know where it went wrong, but a confirmation would be good.

Created attachment 631670 [details]
Test patch for deadlock

Please try this patch. I had not realized until now that a 0 in the timeout parameter in a usb_control_msg() call resulted in an infinite wait. As the callback shows that the interface is shutting down, the possibility exists that there may never be a response and a deadlock.

The test patch sets the timeout to 1000 ms. That should be short enough to prevent the deadlock, but not too short for normal operations.

I built a kernel with Larry's patch
and did not manage to reproduce this deadlock anymore using
while sleep $(($RANDOM%50)) ; do rcwicked restart ; done
so it is probably a good fix.

I have no info about earlier kernels, 
because I only got this system last week
and didnt run it with WLAN before upgrading it to 4.0

Sounds good.

Larry, please let me know if you submit / merge the fix to upstream, so that I can cherry-pick the commit to openSUSE kernels.  Thanks.

For an unknown reason, I missed Bernhard's report that the patch worked. I will push the change as soon as possible. It may take some time before it gets merged, but I will campaign for the patch to be included in kernel 4.1. I will mark it for inclusion in all stable kernels.

Yeah, it's really better to have in 4.1.  It's no "perfect" fix, but practically working.

The fix gets upstreamed, and I backported to SUSE git branches now.

Let's close.

Pushed:
   ad54361ca843..ac673770e1ed  stable^ -> stable

SUSE-SU-2015:1324-1: An update that solves 11 vulnerabilities and has 63 fixes is now available.

Category: security (important)
Bug References: 854817,854824,858727,866911,867362,895814,903279,907092,908491,915183,917630,918618,921430,924071,924526,926369,926953,927455,927697,927786,928131,929475,929696,929879,929974,930092,930399,930579,930599,930972,931124,931403,931538,931620,931860,931988,932348,932793,932897,932898,932899,932900,932967,933117,933429,933637,933896,933904,933907,934160,935083,935085,935088,935174,935542,935881,935918,936012,936423,936445,936446,936502,936556,936831,936875,937032,937087,937609,937612,937613,937616,938022,938023,938024
CVE References: CVE-2014-9728,CVE-2014-9729,CVE-2014-9730,CVE-2014-9731,CVE-2015-1805,CVE-2015-3212,CVE-2015-4036,CVE-2015-4167,CVE-2015-4692,CVE-2015-5364,CVE-2015-5366
Sources used:
SUSE Linux Enterprise Workstation Extension 12 (src):    kernel-default-3.12.44-52.10.1
SUSE Linux Enterprise Software Development Kit 12 (src):    kernel-docs-3.12.44-52.10.3, kernel-obs-build-3.12.44-52.10.1
SUSE Linux Enterprise Server 12 (src):    kernel-default-3.12.44-52.10.1, kernel-source-3.12.44-52.10.1, kernel-syms-3.12.44-52.10.1, kernel-xen-3.12.44-52.10.1
SUSE Linux Enterprise Module for Public Cloud 12 (src):    kernel-ec2-3.12.44-52.10.1
SUSE Linux Enterprise Live Patching 12 (src):    kgraft-patch-SLE12_Update_6-1-2.1
SUSE Linux Enterprise Desktop 12 (src):    kernel-default-3.12.44-52.10.1, kernel-source-3.12.44-52.10.1, kernel-syms-3.12.44-52.10.1, kernel-xen-3.12.44-52.10.1

openSUSE-SU-2015:1382-1: An update that solves 21 vulnerabilities and has 8 fixes is now available.

Category: security (important)
Bug References: 907092,907714,915517,916225,919007,919596,921769,922583,925567,925961,927786,928693,929624,930488,930599,931580,932348,932844,933934,934202,934397,934755,935530,935542,935705,935913,937226,938976,939394
CVE References: CVE-2014-9728,CVE-2014-9729,CVE-2014-9730,CVE-2014-9731,CVE-2015-1420,CVE-2015-1465,CVE-2015-2041,CVE-2015-2922,CVE-2015-3212,CVE-2015-3290,CVE-2015-3339,CVE-2015-3636,CVE-2015-4001,CVE-2015-4002,CVE-2015-4003,CVE-2015-4036,CVE-2015-4167,CVE-2015-4692,CVE-2015-4700,CVE-2015-5364,CVE-2015-5366
Sources used:
openSUSE 13.2 (src):    bbswitch-0.8-3.11.1, cloop-2.639-14.11.1, crash-7.0.8-11.1, hdjmod-1.28-18.12.1, ipset-6.23-11.1, kernel-debug-3.16.7-24.1, kernel-default-3.16.7-24.1, kernel-desktop-3.16.7-24.1, kernel-docs-3.16.7-24.2, kernel-ec2-3.16.7-24.1, kernel-obs-build-3.16.7-24.2, kernel-obs-qa-3.16.7-24.1, kernel-obs-qa-xen-3.16.7-24.1, kernel-pae-3.16.7-24.1, kernel-source-3.16.7-24.1, kernel-syms-3.16.7-24.1, kernel-vanilla-3.16.7-24.1, kernel-xen-3.16.7-24.1, pcfclock-0.44-260.11.1, vhba-kmp-20140629-2.11.1, xen-4.4.2_06-25.1, xtables-addons-2.6-11.1

SUSE-SU-2015:1592-1: An update that solves 14 vulnerabilities and has 45 fixes is now available.

Category: security (important)
Bug References: 851068,867362,873385,883380,886785,894936,915517,917830,919463,920110,920250,920733,921430,923245,924701,925705,925881,925903,926240,926953,927355,927786,929142,929143,930092,930761,930934,931538,932348,932458,933429,933896,933904,933907,933936,934742,934944,935053,935572,935705,935866,935906,936077,936423,936637,936831,936875,936925,937032,937402,937444,937503,937641,937855,939910,939994,940338,940398,942350
CVE References: CVE-2014-9728,CVE-2014-9729,CVE-2014-9730,CVE-2014-9731,CVE-2015-0777,CVE-2015-1420,CVE-2015-1805,CVE-2015-2150,CVE-2015-2830,CVE-2015-4167,CVE-2015-4700,CVE-2015-5364,CVE-2015-5366,CVE-2015-5707
Sources used:
SUSE Linux Enterprise Real Time Extension 11-SP3 (src):    kernel-rt-3.0.101.rt130-0.33.40.1, kernel-rt_trace-3.0.101.rt130-0.33.40.1, kernel-source-rt-3.0.101.rt130-0.33.40.1, kernel-syms-rt-3.0.101.rt130-0.33.40.1
SUSE Linux Enterprise Debuginfo 11-SP3 (src):    kernel-rt-3.0.101.rt130-0.33.40.1, kernel-rt_trace-3.0.101.rt130-0.33.40.1

openSUSE-SU-2016:0301-1: An update that solves 57 vulnerabilities and has 21 fixes is now available.

Category: security (important)
Bug References: 814440,851610,869564,873385,906545,907818,909077,909477,911326,912202,915517,915577,917830,918333,919007,919018,919463,919596,921313,921949,922583,922936,922944,926238,926240,927780,927786,928130,929525,930399,931988,932348,933896,933904,933907,933934,935542,935705,936502,936831,937032,937033,937969,938706,940338,944296,945825,947155,949936,950998,951194,951440,951627,952384,952579,952976,953052,953527,954138,954404,955224,955354,955422,956708,956934,957988,957990,958504,958510,958886,958951,959190,959399,959568,960839,961509,961739,962075
CVE References: CVE-2014-2568,CVE-2014-8133,CVE-2014-8989,CVE-2014-9090,CVE-2014-9419,CVE-2014-9529,CVE-2014-9683,CVE-2014-9715,CVE-2014-9728,CVE-2014-9729,CVE-2014-9730,CVE-2014-9731,CVE-2015-0272,CVE-2015-0777,CVE-2015-1420,CVE-2015-1421,CVE-2015-2041,CVE-2015-2042,CVE-2015-2150,CVE-2015-2666,CVE-2015-2830,CVE-2015-2922,CVE-2015-2925,CVE-2015-3212,CVE-2015-3339,CVE-2015-3636,CVE-2015-4001,CVE-2015-4002,CVE-2015-4003,CVE-2015-4004,CVE-2015-4036,CVE-2015-4167,CVE-2015-4692,CVE-2015-4700,CVE-2015-5157,CVE-2015-5283,CVE-2015-5307,CVE-2015-5364,CVE-2015-5366,CVE-2015-5707,CVE-2015-6937,CVE-2015-7550,CVE-2015-7799,CVE-2015-7833,CVE-2015-7872,CVE-2015-7885,CVE-2015-7990,CVE-2015-8104,CVE-2015-8215,CVE-2015-8543,CVE-2015-8550,CVE-2015-8551,CVE-2015-8552,CVE-2015-8569,CVE-2015-8575,CVE-2015-8767,CVE-2016-0728
Sources used:
openSUSE 13.1 (src):    cloop-2.639-11.22.2, crash-7.0.2-2.22.2, hdjmod-1.28-16.22.2, ipset-6.21.1-2.26.2, iscsitarget-1.4.20.3-13.22.2, kernel-debug-3.11.10-32.1, kernel-default-3.11.10-32.1, kernel-desktop-3.11.10-32.1, kernel-docs-3.11.10-32.3, kernel-ec2-3.11.10-32.1, kernel-pae-3.11.10-32.1, kernel-source-3.11.10-32.1, kernel-syms-3.11.10-32.1, kernel-trace-3.11.10-32.1, kernel-vanilla-3.11.10-32.1, kernel-xen-3.11.10-32.1, ndiswrapper-1.58-22.1, pcfclock-0.44-258.22.1, vhba-kmp-20130607-2.23.1, virtualbox-4.2.36-2.55.1, xen-4.3.4_10-56.1, xtables-addons-2.3-2.22.1