From owner-freebsd-current@FreeBSD.ORG Sun Oct 17 19:17:43 2004 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1D76716A4CE for ; Sun, 17 Oct 2004 19:17:43 +0000 (GMT) Received: from fledge.watson.org (fledge.watson.org [204.156.12.50]) by mx1.FreeBSD.org (Postfix) with ESMTP id AF75043D5D for ; Sun, 17 Oct 2004 19:17:42 +0000 (GMT) (envelope-from robert@fledge.watson.org) Received: from fledge.watson.org (localhost [127.0.0.1]) by fledge.watson.org (8.13.1/8.13.1) with ESMTP id i9HJHcNk032428 for ; Sun, 17 Oct 2004 15:17:38 -0400 (EDT) (envelope-from robert@fledge.watson.org) Received: from localhost (robert@localhost)i9HJHcgZ032425 for ; Sun, 17 Oct 2004 15:17:38 -0400 (EDT) (envelope-from robert@fledge.watson.org) Date: Sun, 17 Oct 2004 15:17:37 -0400 (EDT) From: Robert Watson X-Sender: robert@fledge.watson.org To: current@FreeBSD.org Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Subject: Preemption-related bug in propagate_priority(): it's OK to hold Giant but not be running X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 17 Oct 2004 19:17:43 -0000 Ran into an interesting problem relating to WITNESS and a multiply-destroyed mutex today, but I didn't get the real panic message because of what looks like one or two other bugs. Here's the high-level: sodealloc() tries to destroy the mutex on a socket more than once, causing WITNESS to panic. The soft clock ithread preempts the serial output in panic() when a critical section is released, resulting in a context switch to that ithread. That ithread then attempts to lock a mutex, and is horrified to find out that Giant is held by the thread it preempted, but that that thread isn't blocked: tiger-2# ppanic: process 15955(tcpconnect):2 holds Giant but isn't blocked on a lock % rwatson -- note that double p is from the initiating panic cpuid = 0 KDB: enter: panic [thread 100071] Stopped at kdb_enter+0x2b: nop db> trace kdb_enter(c07fc101) at kdb_enter+0x2b panic(c07ff1ec,3e53,c5f90588,2,c080c957) at panic+0x127 propagate_priority(c547b180,c08c47b8,c5f91780,c08bdbc0,0) at propagate_priority+ 0x139 turnstile_wait(0,c08bdbc0,c5f91780,c08bdbc0,2,c07fb4a5,217) at turnstile_wait+0x 2de _mtx_lock_sleep(c08bdbc0,c547b180,0,c07fd124,f7) at _mtx_lock_sleep+0x15f _mtx_lock_flags(c08bdbc0,0,c07fd124,f7,0) at _mtx_lock_flags+0x85 softclock(0) at softclock+0x16a ithread_loop(c5436e80,e942fd48,c5436e80,c05f7c80,0) at ithread_loop+0x124 fork_exit(c05f7c80,c5436e80,e942fd48) at fork_exit+0xa4 fork_trampoline() at fork_trampoline+0x8 --- trap 0x1, eip = 0, esp = 0xe942fd7c, ebp = 0 --- db> show locks db> show pcpu cpuid = 0 curthread = 0xc547b180: pid 87 "swi4: clock sio" curpcb = 0xe942fda0 fpcurthread = none idlethread = 0xc53e4a80: pid 14 "idle: cpu0" APIC ID = 0 currentldt = 0x28 spin locks held: db> ps pid proc uarea uid ppid pgrp flag stat wmesg wchan cmd 15955 c5f90400 ebbb1000 0 525 15955 0004002 [Can run] tcpconnect ... 87 c548b400 e946e000 0 0 0 000020c [LOCK Giant c5432d00] swi4: clock sio db> trace 15955 sched_switch(c5f91780,c5451d80,6) at sched_switch+0x16f mi_switch(6,c5451d80,c5451ed0,c5451d80,ebba492c) at mi_switch+0x264 maybe_preempt(c5451d80) at maybe_preempt+0x156 sched_add(c5451d80,4,c53e2d80,c5451d80,c5450800) at sched_add+0x153 setrunqueue(c5451d80,4) at setrunqueue+0xab ithread_schedule(c53e2d80,1f,c5f91780,c5f91780,2580) at ithread_schedule+0xb3 intr_execute_handlers(c53dc0d8,ebba49a8,1f,ebba49f0,c0780ad3) at intr_execute_ha ndlers+0xf5 lapic_handle_intr(4f) at lapic_handle_intr+0x2e Xapic_isr2() at Xapic_isr2+0x33 --- interrupt, eip = 0xc0619446, esp = 0xebba49ec, ebp = 0xebba49f0 --- critical_exit(3f8,ebba4a30,c076f731,c08fa000,0) at critical_exit+0x92 _mtx_unlock_spin_flags(c08fa000,0,c08174fc,be4) at _mtx_unlock_spin_flags+0x8d siocnputc(c08987c0,70) at siocnputc+0xb9 cnputc(70) at cnputc+0x4d putchar(70,ebba4b44) at putchar+0x52 kvprintf(c07fc2ed,c06219b8,ebba4b44,a,ebba4b64) at kvprintf+0x77 printf(c07fc2ed,c08bf060,c08bf060,100,c07ff91e,ebba4b98) at printf+0x43 panic(c07ff91e,c07b69b1,c0813aa8,c07ff6af,c5a23ebc) at panic+0xcb witness_destroy(c5a23ebc,c5a23dec,ebba4bd0,c063f15f,c5a23ebc) at witness_destroy +0x40 mtx_destroy(c5a23ebc,c5e94e00,c5a23ebc,ebba4be8,c063f4fd) at mtx_destroy+0x7a sodealloc(c5a23dec,c5a23eb0,c5832bb0,c5a23dec,ebba4c00) at sodealloc+0xf3 sofree(c5a23dec) at sofree+0x281 soclose(c5a23dec,c5832bb0,0,ebba4c2c,c05efad0) at soclose+0x24d soo_close(c5832bb0,c5f91780) at soo_close+0x4b fdrop_locked(c5832bb0,c5f91780,c53ccf40,0,c07f90b1) at fdrop_locked+0x84 fdrop(c5832bb0,c5f91780,ebba4c78,c0628c5c,c07f90ba) at fdrop+0x24 closef(c5832bb0,c5f91780,c5ebc628,0,c07f90b1) at closef+0x1db close(c5f91780,ebba4d14,1,14b,292) at close+0xe6 syscall(2f,bfbf002f,bfbf002f,3,bfbfedf7) at syscall+0x213 Xint0x80_syscall() at Xint0x80_syscall+0x1f --- syscall (6, FreeBSD ELF32, close), eip = 0x280c154b, esp = 0xbfbfec0c, ebp = 0xbfbfec48 --- db> show locks 15955 exclusive sleep mutex Giant r = 0 (0xc08bdbc0) locked @ kern/kern_descrip.c:967 So on face value, it looks like propagate_priority() is unhappy about the tcpconnect thread (that was preempted) still holding Giant. However, given that preemption is supposed to preempt but leave a thread runnable, this would seem not to be a panic-worthy condition. Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Principal Research Scientist, McAfee Research