Hi Oliver, I love your patch! Perhaps something to improve: [auto build test WARNING on usb/usb-testing] [also build test WARNING on v5.9-rc6 next-20200921] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in https://git-scm.com/docs/git-format-patch] url: https://github.com/0day-ci/linux/commits/Oliver-Neukum/chaoskey-O_NONBLOC... base: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing config: sh-allmodconfig (attached as .config) compiler: sh4-linux-gcc (GCC) 9.3.0 reproduce (this is a W=1 build): wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross # save the attached .config to linux build tree COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=sh If you fix the issue, kindly add following tag as appropriate Reported-by: kernel test robot <lkp(a)intel.com&gt; All warnings (new ones prefixed by >>): drivers/usb/misc/chaoskey.c: In function 'chaoskey_request_fill': 340 | bool started; | ^~~~~~~ # https://github.com/0day-ci/linux/commit/4393931662d77cd7c609d4cfd82ad5990... git remote add linux-review https://github.com/0day-ci/linux git fetch --no-tags linux-review Oliver-Neukum/chaoskey-O_NONBLOCK-in-concurrent-reads/20200921-203804 git checkout 4393931662d77cd7c609d4cfd82ad59900c9b13b vim +/started +340 drivers/usb/misc/chaoskey.c 0ca10122ca08d2 Oliver Neukum 2016-02-17 335 4393931662d77c Oliver Neukum 2020-09-21 336 static int chaoskey_request_fill(struct chaoskey *dev) 66e3e591891da9 Keith Packard 2015-03-19 337 { 66e3e591891da9 Keith Packard 2015-03-19 338 DEFINE_WAIT(wait); 66e3e591891da9 Keith Packard 2015-03-19 339 int result; e4a886e811cd07 Bob Ham 2016-06-03 @340 bool started; 66e3e591891da9 Keith Packard 2015-03-19 341 4393931662d77c Oliver Neukum 2020-09-21 342 usb_dbg(dev->interface, "request fill"); 66e3e591891da9 Keith Packard 2015-03-19 343 66e3e591891da9 Keith Packard 2015-03-19 344 /* Return immediately if someone called before the buffer was 66e3e591891da9 Keith Packard 2015-03-19 345 * empty */ 66e3e591891da9 Keith Packard 2015-03-19 346 if (dev->valid != dev->used) { 66e3e591891da9 Keith Packard 2015-03-19 347 usb_dbg(dev->interface, "not empty yet (valid %d used %d)", 66e3e591891da9 Keith Packard 2015-03-19 348 dev->valid, dev->used); 66e3e591891da9 Keith Packard 2015-03-19 349 return 0; 66e3e591891da9 Keith Packard 2015-03-19 350 } 66e3e591891da9 Keith Packard 2015-03-19 351 66e3e591891da9 Keith Packard 2015-03-19 352 /* Bail if the device has been removed */ 66e3e591891da9 Keith Packard 2015-03-19 353 if (!dev->present) { 66e3e591891da9 Keith Packard 2015-03-19 354 usb_dbg(dev->interface, "device not present"); 66e3e591891da9 Keith Packard 2015-03-19 355 return -ENODEV; 66e3e591891da9 Keith Packard 2015-03-19 356 } 66e3e591891da9 Keith Packard 2015-03-19 357 66e3e591891da9 Keith Packard 2015-03-19 358 /* Make sure the device is awake */ 66e3e591891da9 Keith Packard 2015-03-19 359 result = usb_autopm_get_interface(dev->interface); 66e3e591891da9 Keith Packard 2015-03-19 360 if (result) { 66e3e591891da9 Keith Packard 2015-03-19 361 usb_dbg(dev->interface, "wakeup failed (result %d)", result); 66e3e591891da9 Keith Packard 2015-03-19 362 return result; 66e3e591891da9 Keith Packard 2015-03-19 363 } 66e3e591891da9 Keith Packard 2015-03-19 364 0ca10122ca08d2 Oliver Neukum 2016-02-17 365 dev->reading = true; 0ca10122ca08d2 Oliver Neukum 2016-02-17 366 result = usb_submit_urb(dev->urb, GFP_KERNEL); 0ca10122ca08d2 Oliver Neukum 2016-02-17 367 if (result < 0) { 0ca10122ca08d2 Oliver Neukum 2016-02-17 368 result = usb_translate_errors(result); 0ca10122ca08d2 Oliver Neukum 2016-02-17 369 dev->reading = false; 0ca10122ca08d2 Oliver Neukum 2016-02-17 370 goto out; 0ca10122ca08d2 Oliver Neukum 2016-02-17 371 } 0ca10122ca08d2 Oliver Neukum 2016-02-17 372 e4a886e811cd07 Bob Ham 2016-06-03 373 /* The first read on the Alea takes a little under 2 seconds. e4a886e811cd07 Bob Ham 2016-06-03 374 * Reads after the first read take only a few microseconds e4a886e811cd07 Bob Ham 2016-06-03 375 * though. Presumably the entropy-generating circuit needs e4a886e811cd07 Bob Ham 2016-06-03 376 * time to ramp up. So, we wait longer on the first read. e4a886e811cd07 Bob Ham 2016-06-03 377 */ e4a886e811cd07 Bob Ham 2016-06-03 378 started = dev->reads_started; e4a886e811cd07 Bob Ham 2016-06-03 379 dev->reads_started = true; 4393931662d77c Oliver Neukum 2020-09-21 380 /* 4393931662d77c Oliver Neukum 2020-09-21 381 * powering down while a read is under way 4393931662d77c Oliver Neukum 2020-09-21 382 * is blocked in suspend() 4393931662d77c Oliver Neukum 2020-09-21 383 */ 4393931662d77c Oliver Neukum 2020-09-21 384 usb_autopm_put_interface(dev->interface); 4393931662d77c Oliver Neukum 2020-09-21 385 return 0; 4393931662d77c Oliver Neukum 2020-09-21 386 out: 4393931662d77c Oliver Neukum 2020-09-21 387 usb_autopm_put_interface(dev->interface); 4393931662d77c Oliver Neukum 2020-09-21 388 return result; 4393931662d77c Oliver Neukum 2020-09-21 389 } 4393931662d77c Oliver Neukum 2020-09-21 390 --- 0-DAY CI Kernel Test Service, Intel Corporation https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org