Now let me describe where the race is: Thread A: | Thread B: cv_timedwait() | softclock() | cv_timedwait_end() | mtx_lock_spin(&sched_lock); | mtx_lock_spin(&sched_lock); /* suppose blocked!!! */ ... | callout_stop(&td->td_slpcallout) | td->td_flags |= TDF_TIMEOUT; | td->td_proc->p_stats->p_ru.ru_nivcsw++; | // problem, does not set thread state to TDS_SLP!!! | mi_switch(); | // run at once again | ... | mtx_unlock_spin(&sched_lock); | mtx_lock_spin() returned !!! thread is still running | if (td->td_flags & TDF_TIMEOUT) { ... | td->td_flags &= ~TDF_TIMEOUT; some place call mi_switch() and now on runqueue | setrunqueue(td); // crash | }
---------------------------------------------------------- here is the patch: --- /sys/kern/kern_condvar.c.old Mon Jul 1 09:06:01 2002 +++ /sys/kern/kern_condvar.c Mon Jul 1 09:32:50 2002 @@ -396,6 +396,7 @@ * between msleep and endtsleep. */ td->td_flags |= TDF_TIMEOUT; + td->td_state = TDS_SLP; td->td_proc->p_stats->p_ru.ru_nivcsw++; mi_switch(); } @@ -472,6 +473,7 @@ * between msleep and endtsleep. */ td->td_flags |= TDF_TIMEOUT; + td->td_state = TDS_SLP; td->td_proc->p_stats->p_ru.ru_nivcsw++; mi_switch(); } ------------------------------------------------------------------- bug is because cv_timedwait() detects timeout callout is running, but it does not correctly wait callout to complete, so panic. BTW, the bug seems also exists in msleep() and endtsleep(), please fix it! -David Xu --- David Xu <[EMAIL PROTECTED]> wrote: > setrunqueue() call can be simply removed from cv_timedwait_end(), because > there > is a race in softclock() and callout_stop(), when cv_timedwait_end() losts a > race, it means that that thread is already running(wokenup by another > thread), > when you setrunqueue() it, of course it will panic. > in cv_timedwait_end(), sentence "if (td->td_flags & TDF_TIMEOUT) {...}" > is to check this race condition. > > -David Xu > > ----- Original Message ----- > From: "Matthew Dillon" <[EMAIL PROTECTED]> > To: "Julian Elischer" <[EMAIL PROTECTED]> > Cc: "Steve Kargl" <[EMAIL PROTECTED]>; "walt" > <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> > Sent: Monday, July 01, 2002 4:43 AM > Subject: KSE / interrupt panic > > > > Got another one. Different panic, same place. > > > > panic: setrunqueue: bad thread state > > cpuid = 0; lapic.id = 01000000 > > Debugger("panic") > > Stopped at Debugger+0x46: xchgl %ebx,in_Debugger.0 > > db> trace > > Debugger(c02ec2ba) at Debugger+0x46 > > panic(c02ec8a9,c6461d80,c6461d80,c6461d80,c01afa30) at panic+0xd6 > > setrunqueue(c6461d80) at setrunqueue+0x1dd > > cv_timedwait_end(c6461d80) at cv_timedwait_end+0x36 > > softclock(0) at softclock+0x159 > > ithread_loop(c229c700,df3eed48,c22aec00,c01b9c6c,0) at ithread_loop+0x12c > > fork_exit(c01b9c6c,c229c700,df3eed48) at fork_exit+0xa8 > > fork_trampoline() at fork_trampoline+0x37 > > db> gdb > > ... > > > > #0 Debugger (msg=0xc02ec2ba "panic") > > at /FreeBSD/FreeBSD-current/src/sys/i386/i386/db_interface.c:324 > > #1 0xc01c878a in panic (fmt=0xc02ec8a9 "setrunqueue: bad thread state") > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_shutdown.c:482 > > #2 0xc01cc6cd in setrunqueue (td=0xc6461d80) > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_switch.c:396 > > #3 0xc01afa66 in cv_timedwait_end (arg=0xc6461d80) > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_condvar.c:608 > > #4 0xc01d22c9 in softclock (dummy=0x0) > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_timeout.c:187 > > #5 0xc01b9d98 in ithread_loop (arg=0xc229c700) > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_intr.c:535 > > #6 0xc01b923c in fork_exit (callout=0xc01b9c6c <ithread_loop>, > > arg=0xc229c700, frame=0xdf3eed48) > > at /FreeBSD/FreeBSD-current/src/sys/kern/kern_fork.c:863 > > > > I'm not sure why the panic was 'bad thread state' when gdb seems to > > show it being stuck on 'unexpected ke present'. Maybe it was an > > optimization and gdb is confused. The panic is definitely > > 'bad thread state'. > > > > (gdb) print td->td_state > > $2 = TDS_RUNQ > > > > setrunqueue() is being called on a thread which is already on the run > > queue. > > > > -Matt > > > > > > To Unsubscribe: send mail to [EMAIL PROTECTED] > > with "unsubscribe freebsd-current" in the body of the message > > __________________________________________________ > Do You Yahoo!? > Yahoo! - Official partner of 2002 FIFA World Cup > http://fifaworldcup.yahoo.com > To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-current" in the body of the message