Re: panic in deadlkres

2010/6/28 John Baldwin <jhb_at_freebsd.org>:
> On Friday 25 June 2010 4:52:22 pm pluknet wrote:
>> On 25 June 2010 13:50, Anton Yuzhaninov <citrin_at_citrin.ru> wrote:
>> > I've got panic on 9-current from Jun 25 2010
>> >
>> > May be this is bug in deadlock resolver
>> >
>> > panic: blockable sleep lock (sleep mutex) process lock _at_
>> > /usr/src/sys/kern/kern_clock.c:203
>> >
>> > db> show alllocks
>> > Process 0 (kernel) thread 0xc4dcd270 (100047)
>> > shared sx allproc (allproc) r = 0 (0xc0885ebc) locked _at_
>> > /usr/src/sys/kern/kern_clock.c:193
>> >
>> > db> show lock 0xc4dcd270
>> >  class: spin mutex
>> >  name: D
>> >  flags: {SPIN, RECURSE}
>> >  state: {OWNED}
>> >
>> > (kgdb) bt
>> > #0  doadump () at pcpu.h:248
>> > #1  0xc05ae59f in boot (howto=260) at
> /usr/src/sys/kern/kern_shutdown.c:416
>> > #2  0xc05ae825 in panic (fmt=Variable "fmt" is not available.
>> > ) at /usr/src/sys/kern/kern_shutdown.c:590
>> > #3  0xc048ff45 in db_panic (addr=Could not find the frame base for
> "db_panic".
>> > ) at /usr/src/sys/ddb/db_command.c:478
>> > #4  0xc0490533 in db_command (last_cmdp=0xc086ef1c, cmd_table=0x0,
> dopager=1) at /usr/src/sys/ddb/db_command.c:445
>> > #5  0xc0490662 in db_command_loop () at /usr/src/sys/ddb/db_command.c:498
>> > #6  0xc04923ef in db_trap (type=3, code=0) at
> /usr/src/sys/ddb/db_main.c:229
>> > #7  0xc05dade6 in kdb_trap (type=3, code=0, tf=0xc4b31bd0) at
> /usr/src/sys/kern/subr_kdb.c:535
>> > #8  0xc078696b in trap (frame=0xc4b31bd0) at
> /usr/src/sys/i386/i386/trap.c:692
>> > #9  0xc076ca0b in calltrap () at /usr/src/sys/i386/i386/exception.s:165
>> > #10 0xc05daf30 in kdb_enter (why=0xc07ea02d "panic", msg=0xc07ea02d
> "panic") at cpufunc.h:71
>> > #11 0xc05ae806 in panic (fmt=0xc07efd94 "blockable sleep lock (%s) %s _at_
> %s:%d") at /usr/src/sys/kern/kern_shutdown.c:573
>> > #12 0xc05ee30b in witness_checkorder (lock=0xc5148088, flags=9,
> file=0xc07e3b20 "/usr/src/sys/kern/kern_clock.c", line=203, interlock=0x0)
>> >    at /usr/src/sys/kern/subr_witness.c:1067
>> > #13 0xc05a093c in _mtx_lock_flags (m=0xc5148088, opts=0, file=0xc07e3b20
> "/usr/src/sys/kern/kern_clock.c", line=203)
>> >    at /usr/src/sys/kern/kern_mutex.c:200
>> > #14 0xc05706a9 in deadlkres () at /usr/src/sys/kern/kern_clock.c:203
>> > #15 0xc0588721 in fork_exit (callout=0xc05705ea <deadlkres>, arg=0x0,
> frame=0xc4b31d38) at /usr/src/sys/kern/kern_fork.c:843
>> > #16 0xc076ca80 in fork_trampoline () at
> /usr/src/sys/i386/i386/exception.s:270
>>
>> Hi!
>>
>> [throw in ideas (just ignore them if they're dumb, thinking badly atm).]
>>
>> AFAIK, that indicates that some thread already has
>> a spin mutex and then it tries to acquire a sleep mutex.
>>
>> Looks like kern/kern_clock.c v1.213 (SVN rev 206482)
>> has a regression in handling ticks wrap-up
>> w.r.t. it doesn't release a thread mutex, does it?
>
> This looks like a correct analysis to me.
>
>> >From subr_witness.c:
>> 1062:                 * Since spin locks include a critical section, this
> check
>> 1063:                 * implicitly enforces a lock order of all sleep
>> locks before
>> 1064:                 * all spin locks.
>> 1065:                 */
>> 1066:                if (td->td_critnest != 0 && !kdb_active)
>> 1067:                        panic("blockable sleep lock (%s) %s _at_ %s:%d",
>> 1068:                            class->lc_name, lock->lo_name, file, line);
>>
>> >From kern_clock.c, v1.213 (in several places, while holding a thread lock):
>> +                                     /* Handle ticks wrap-up. */
>> +                                     if (ticks < td->td_blktick)
>> +                                             continue;
>>
>> Should not it be like the next:
>> +                                     /* Handle ticks wrap-up. */
>> +                                     if (ticks < td->td_blktick) {
>> +                                             thread_unlock(td);
>> +                                             continue;
>> +                                     }
>>
>> The precondition idea to reproduce it is to lock a subject thread
>> in some deadlkres callout, handle re-wrap condition, then try
>> to lock a process to witch the thread belongs in (n+m)'th deadlkres
>> callout, or in different context.

Thanks, that may be fixed in r209577.

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein