Red Hat Bugzilla – Bug 125482
Badness in interruptible_sleep_on_timeout at kernel/sched.c:1942
Last modified: 2007-11-30 17:10:44 EST
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040510 Description of problem: I have developed a USB driver which worked OK under Fedora Core 1. Under Fedora Core 2 I get some panic-like messages in /var/log/messages when the driver is loaded. Since the panic seems to be in sched.c I it isn't obvious how this is caused by my code. I don't use interruptible_sleep_on_timout in my driver. My driver uses wait_event_interruptible_timeout. ~ Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: 1.Load my device driver (obviously you can't reproduce this) 2. 3. Actual Results: Panic messages shown in attachment Expected Results: No panic messages Additional info:
Created attachment 100945 [details] Portion of /var/log/messages I don't know why the panic occurs 10 times.
I looked into sched.c. It is using SLEEP_ON_BKLCHECK which is defined as: #define SLEEP_ON_BKLCHECK \ if (unlikely(!kernel_locked()) && \ sleep_on_bkl_warnings < 10) { \ sleep_on_bkl_warnings++; \ WARN_ON(1); \ } There is the reason for 10 panic (wanrning?) messages. But what does 'unlikely(!kernel_locked())' mean? P.S. My real name is Richard Stover - I thought I filled in that field...
using *_sleep_on without BKL is quite a bad/nasty bug so we moan loudly. (well technically using interruptible_sleep_on is *almost* always a bug but with BKL you actually *can* use it correct) if your driver is open source (it is GPL, right?) then it would be nice if you could put a pointer to it somewhere so that I can check this thing out better
I have placed my driver source code here: ftp://www.ccd.ucolick.org/pub/usbfo The warning messages are generated from line 3071 of usbfo.c I thought of another possibly related issue. I tried to replace all of my init_waitqueue_head() calls with DECLARE_WAIT_QUEUE_HEAD() but I always get a syntax error. For instance, replace line 3937, init_waitqueue_head(&(dev->wait)); with DECLARE_WAIT_QUEUE_HEAD(dev->wait); Shouldn't this work? And is it at all related to the BKL problem?
I don't quite yet see how wait_event_interruptible_timeout leads to interruptible_sleep_* ....
We'll I'm baffled now. The warnings are no longer happening! I'm running the exact same driver code. There must be some sequence of things that has to happen for the interruptible_sleep* to be triggered. I see a few instances of interruptible_sleep_* still in the FC2 source code in drivers/usb/* but I don't see why any of that code should be involved. I'll have to pick this up again when I get back from vacation.