Re: [PATCH 4.19 regression fix] printk: For early boot messages check loglevel when flushing the buffer

From: kbuild test robot
Date: Thu Sep 06 2018 - 10:36:39 EST

Hi Hans,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.19-rc2 next-20180906]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Hans-de-Goede/printk-For-early-boot-messages-check-loglevel-when-flushing-the-buffer/20180906-215356
config: parisc-allnoconfig (attached as .config)
compiler: hppa-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
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
GCC_VERSION=7.2.0 make.cross ARCH=parisc

All errors (new ones prefixed by >>):

kernel/printk/printk.c: In function 'console_unlock':
>> kernel/printk/printk.c:2377:5: error: implicit declaration of function 'suppress_message_printing' [-Werror=implicit-function-declaration]
suppress_message_printing(msg->level))) {
^~~~~~~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors

vim +/suppress_message_printing +2377 kernel/printk/printk.c

2297
2298 /**
2299 * console_unlock - unlock the console system
2300 *
2301 * Releases the console_lock which the caller holds on the console system
2302 * and the console driver list.
2303 *
2304 * While the console_lock was held, console output may have been buffered
2305 * by printk(). If this is the case, console_unlock(); emits
2306 * the output prior to releasing the lock.
2307 *
2308 * If there is output waiting, we wake /dev/kmsg and syslog() users.
2309 *
2310 * console_unlock(); may be called from any context.
2311 */
2312 void console_unlock(void)
2313 {
2314 static char ext_text[CONSOLE_EXT_LOG_MAX];
2315 static char text[LOG_LINE_MAX + PREFIX_MAX];
2316 unsigned long flags;
2317 bool do_cond_resched, retry;
2318
2319 if (console_suspended) {
2320 up_console_sem();
2321 return;
2322 }
2323
2324 /*
2325 * Console drivers are called with interrupts disabled, so
2326 * @console_may_schedule should be cleared before; however, we may
2327 * end up dumping a lot of lines, for example, if called from
2328 * console registration path, and should invoke cond_resched()
2329 * between lines if allowable. Not doing so can cause a very long
2330 * scheduling stall on a slow console leading to RCU stall and
2331 * softlockup warnings which exacerbate the issue with more
2332 * messages practically incapacitating the system.
2333 *
2334 * console_trylock() is not able to detect the preemptive
2335 * context reliably. Therefore the value must be stored before
2336 * and cleared after the the "again" goto label.
2337 */
2338 do_cond_resched = console_may_schedule;
2339 again:
2340 console_may_schedule = 0;
2341
2342 /*
2343 * We released the console_sem lock, so we need to recheck if
2344 * cpu is online and (if not) is there at least one CON_ANYTIME
2345 * console.
2346 */
2347 if (!can_use_console()) {
2348 console_locked = 0;
2349 up_console_sem();
2350 return;
2351 }
2352
2353 for (;;) {
2354 struct printk_log *msg;
2355 size_t ext_len = 0;
2356 size_t len;
2357
2358 printk_safe_enter_irqsave(flags);
2359 raw_spin_lock(&logbuf_lock);
2360 if (console_seq < log_first_seq) {
2361 len = sprintf(text, "** %u printk messages dropped **\n",
2362 (unsigned)(log_first_seq - console_seq));
2363
2364 /* messages are gone, move to first one */
2365 console_seq = log_first_seq;
2366 console_idx = log_first_idx;
2367 } else {
2368 len = 0;
2369 }
2370 skip:
2371 if (console_seq == log_next_seq)
2372 break;
2373
2374 msg = log_from_idx(console_idx);
2375 if ((msg->flags & LOG_NOCONS) ||
2376 ((msg->flags & LOG_CHK_LEVEL) &&
> 2377 suppress_message_printing(msg->level))) {
2378 /*
2379 * Skip record if !ignore_loglevel, and
2380 * record has level above the console loglevel.
2381 */
2382 console_idx = log_next(console_idx);
2383 console_seq++;
2384 goto skip;
2385 }
2386
2387 len += msg_print_text(msg,
2388 console_msg_format & MSG_FORMAT_SYSLOG,
2389 text + len,
2390 sizeof(text) - len);
2391 if (nr_ext_console_drivers) {
2392 ext_len = msg_print_ext_header(ext_text,
2393 sizeof(ext_text),
2394 msg, console_seq);
2395 ext_len += msg_print_ext_body(ext_text + ext_len,
2396 sizeof(ext_text) - ext_len,
2397 log_dict(msg), msg->dict_len,
2398 log_text(msg), msg->text_len);
2399 }
2400 console_idx = log_next(console_idx);
2401 console_seq++;
2402 raw_spin_unlock(&logbuf_lock);
2403
2404 /*
2405 * While actively printing out messages, if another printk()
2406 * were to occur on another CPU, it may wait for this one to
2407 * finish. This task can not be preempted if there is a
2408 * waiter waiting to take over.
2409 */
2410 console_lock_spinning_enable();
2411
2412 stop_critical_timings(); /* don't trace print latency */
2413 call_console_drivers(ext_text, ext_len, text, len);
2414 start_critical_timings();
2415
2416 if (console_lock_spinning_disable_and_check()) {
2417 printk_safe_exit_irqrestore(flags);
2418 return;
2419 }
2420
2421 printk_safe_exit_irqrestore(flags);
2422
2423 if (do_cond_resched)
2424 cond_resched();
2425 }
2426
2427 console_locked = 0;
2428
2429 /* Release the exclusive_console once it is used */
2430 if (unlikely(exclusive_console))
2431 exclusive_console = NULL;
2432
2433 raw_spin_unlock(&logbuf_lock);
2434
2435 up_console_sem();
2436
2437 /*
2438 * Someone could have filled up the buffer again, so re-check if there's
2439 * something to flush. In case we cannot trylock the console_sem again,
2440 * there's a new owner and the console_unlock() from them will do the
2441 * flush, no worries.
2442 */
2443 raw_spin_lock(&logbuf_lock);
2444 retry = console_seq != log_next_seq;
2445 raw_spin_unlock(&logbuf_lock);
2446 printk_safe_exit_irqrestore(flags);
2447
2448 if (retry && console_trylock())
2449 goto again;
2450 }
2451 EXPORT_SYMBOL(console_unlock);
2452

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation

Attachment: .config.gz
Description: application/gzip