Date: Wed, 17 Jun 2009 08:15:26 -0400 From: John Baldwin <jhb@freebsd.org> To: Mel Flynn <mel.flynn+fbsd.hackers@mailing.thruhere.net> Cc: freebsd-hackers@freebsd.org Subject: Re: How best to debug locking/scheduler problems Message-ID: <200906170815.26650.jhb@freebsd.org> In-Reply-To: <200906161501.45411.mel.flynn%2Bfbsd.hackers@mailing.thruhere.net> References: <200906151353.06630.mel.flynn%2Bfbsd.hackers@mailing.thruhere.net> <200906161502.42741.jhb@freebsd.org> <200906161501.45411.mel.flynn%2Bfbsd.hackers@mailing.thruhere.net>
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On Tuesday 16 June 2009 7:01:45 pm Mel Flynn wrote: > On Tuesday 16 June 2009 11:02:42 John Baldwin wrote: > > On Tuesday 16 June 2009 1:52:23 pm Mel Flynn wrote: > > > Hi John, > > > > > > On Tuesday 16 June 2009 04:19:57 John Baldwin wrote: > > > > On Monday 15 June 2009 5:53:05 pm Mel Flynn wrote: > > > > > PID TID COMM TDNAME KSTACK > > > > > 4283 100215 kdeinit4 - mi_switch > > > > > turnstile_wait _mtx_lock_sleep uipc_peeraddr kern_getpeername > > > > > getpeername syscall Xint0x80_syscall > > > > > % ps -ww 4283 > > > > > PID TT STAT TIME COMMAND > > > > > 4283 ?? T 0:00.38 kdeinit4: kdeinit4: kio_http http > > > > > local:/tmp/ksocket-mel/klauncherxJ1635.slave-socket > > > > > local:/tmp/ksocket- mel/plasmayC1653.slave-socket (kdeinit4) > > > > > > > > > > %ls -l /tmp/ksocket-mel/ > > > > > > > > > > total 2 > > > > > -rw-rw-r-- 1 mel wheel 62 Jun 14 22:55 KSMserver__0 > > > > > srw------- 1 mel wheel 0 Jun 14 22:55 kdeinit4__0 > > > > > srwxrwxr-x 1 mel wheel 0 Jun 14 22:55 > > > > > klauncherxJ1635.slave-socket > > > > > > > > You can use kgdb and the scripts at www.freebsd.org/~jhb/gdb. Simply > > > > run 'kgdb' as root and do 'lcd /folder/with/scripts' and 'source gdb6'. > > > > You can then do 'lockchain 4283' to find who holds the lock this thread > > > > is blocked on and what state they are in. > > > > > > Looks like a deadlock: > > > > > > (kgdb) lockchain 4283 > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > thread 100215 (pid 4283, kdeinit4) blocked on lock 0xc64374a0 "unp_mtx" > > > thread 100122 (pid 1635, klauncher) blocked on lock 0xc6806348 "unp_mtx" > > > DEADLOCK > > > > > > Looking through the scripts now to see how I can get more info on the > > > call chain and hoping I don't panic the machine ;). It is quite random to > > > reproduce. > > > > In kgdb you can simply do 'tid 100122' followed by 'bt' and 'tid 100215' > > followed by 'bt'. > > Cool, thanks for helping John. Of course it pretty much shows me what procstat > -k shows and can't get any info on the userland part, but I can fully inspect > the locks and threads. > > Both threads are in TDS_INHIBITED state, and blocked on: > (kgdb) frame 0 > #0 sched_switch (td=0xc5971240, newtd=0xc4d39900, flags=259) > at /usr/src/sys/kern/sched_ule.c:1864 > 1864 cpuid = PCPU_GET(cpuid); That doesn't really tell us anything except that it isn't running. We know it is actually blocked on a lock, and we need the full stack trace to see where the two threads were trying to acquire the locks, hence 'bt'. ' procstat -k' output would be fine, too. -- John Baldwin
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