1 /*-
2 * Copyright (c) 2004 Robert N. M. Watson
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
27 */
28
29 #include "opt_mp_watchdog.h"
30 #include "opt_sched.h"
31
32 #ifdef SCHED_ULE
33 #error MP_WATCHDOG cannot currently be used with SCHED_ULE
34 #endif
35
36 #include <sys/param.h>
37 #include <sys/kdb.h>
38 #include <sys/kernel.h>
39 #include <sys/lock.h>
40 #include <sys/mutex.h>
41 #include <sys/pcpu.h>
42 #include <sys/proc.h>
43 #include <sys/sysctl.h>
44 #include <sys/systm.h>
45
46 #include <machine/smp.h>
47 #include <x86/apicreg.h>
48 #include <x86/apicvar.h>
49 #include <machine/mp_watchdog.h>
50
51 /*
52 * mp_watchdog hijacks the idle thread on a specified CPU, prevents new work
53 * from being scheduled there, and uses it as a "watchdog" to detect kernel
54 * failure on other CPUs. This is made reasonable by inclusion of logical
55 * processors in Xeon hardware. The watchdog is configured by setting the
56 * debug.watchdog sysctl/tunable to the CPU of interest. A callout will then
57 * begin executing reseting a timer that is gradually lowered by the watching
58 * thread. If the timer reaches 0, the watchdog fires by ether dropping
59 * directly to the debugger, or by sending an NMI IPI to the boot processor.
60 * This is a somewhat less efficient substitute for dedicated watchdog
61 * hardware, but can be quite an effective tool for debugging hangs.
62 *
63 * XXXRW: This should really use the watchdog(9)/watchdog(4) framework, but
64 * doesn't yet.
65 */
66 static int watchdog_cpu = -1;
67 static int watchdog_dontfire = 1;
68 static int watchdog_timer = -1;
69 static int watchdog_nmi = 1;
70
71 SYSCTL_INT(_debug, OID_AUTO, watchdog_nmi, CTLFLAG_RWTUN, &watchdog_nmi, 0,
72 "IPI the boot processor with an NMI to enter the debugger");
73
74 static struct callout watchdog_callout;
75
76 static void watchdog_change(int wdcpu);
77
78 /*
79 * Number of seconds before the watchdog will fire if the callout fails to
80 * reset the timer.
81 */
82 #define WATCHDOG_THRESHOLD 10
83
84 static void
watchdog_init(void * arg)85 watchdog_init(void *arg)
86 {
87
88 callout_init(&watchdog_callout, 1);
89 if (watchdog_cpu != -1)
90 watchdog_change(watchdog_cpu);
91 }
92
93 /*
94 * This callout resets a timer until the watchdog kicks in. It acquires some
95 * critical locks to make sure things haven't gotten wedged with those locks
96 * held.
97 */
98 static void
watchdog_function(void * arg)99 watchdog_function(void *arg)
100 {
101
102 /*
103 * Since the timer ran, we must not be wedged. Acquire some critical
104 * locks to make sure. Then reset the timer.
105 */
106 mtx_lock(&Giant);
107 watchdog_timer = WATCHDOG_THRESHOLD;
108 mtx_unlock(&Giant);
109 callout_reset(&watchdog_callout, 1 * hz, watchdog_function, NULL);
110 }
111 SYSINIT(watchdog_init, SI_SUB_DRIVERS, SI_ORDER_ANY, watchdog_init, NULL);
112
113 static void
watchdog_change(int wdcpu)114 watchdog_change(int wdcpu)
115 {
116
117 if (wdcpu == -1 || wdcpu == 0xffffffff) {
118 /*
119 * Disable the watchdog.
120 */
121 watchdog_cpu = -1;
122 watchdog_dontfire = 1;
123 callout_stop(&watchdog_callout);
124 printf("watchdog stopped\n");
125 } else {
126 watchdog_timer = WATCHDOG_THRESHOLD;
127 watchdog_dontfire = 0;
128 watchdog_cpu = wdcpu;
129 callout_reset(&watchdog_callout, 1 * hz, watchdog_function,
130 NULL);
131 }
132 }
133
134 /*
135 * This sysctl sets which CPU is the watchdog CPU. Set to -1 or 0xffffffff
136 * to disable the watchdog.
137 */
138 static int
sysctl_watchdog(SYSCTL_HANDLER_ARGS)139 sysctl_watchdog(SYSCTL_HANDLER_ARGS)
140 {
141 int error, temp;
142
143 temp = watchdog_cpu;
144 error = sysctl_handle_int(oidp, &temp, 0, req);
145 if (error)
146 return (error);
147
148 if (req->newptr != NULL)
149 watchdog_change(temp);
150 return (0);
151 }
152 SYSCTL_PROC(_debug, OID_AUTO, watchdog,
153 CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
154 0, 0, sysctl_watchdog, "I",
155 "");
156
157 /*
158 * Drop into the debugger by sending an IPI NMI to the boot processor.
159 */
160 static void
watchdog_ipi_nmi(void)161 watchdog_ipi_nmi(void)
162 {
163
164 /*
165 * Deliver NMI to the boot processor. Why not?
166 */
167 lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
168 APIC_LEVEL_ASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_NMI,
169 boot_cpu_id);
170 lapic_ipi_wait(-1);
171 }
172
173 /*
174 * ap_watchdog() is called by the SMP idle loop code. It works on the same
175 * premise that the disabling of logical processors does: that if the cpu is
176 * idle, then it can ignore the world from then on, as nothing will be
177 * scheduled on it. Leaving aside multi-runqueue schedulers (SCHED_ULE) and
178 * explicit process migration (sched_bind()), this is not an unreasonable
179 * assumption.
180 */
181 void
ap_watchdog(u_int cpuid)182 ap_watchdog(u_int cpuid)
183 {
184 char old_pcomm[MAXCOMLEN + 1];
185 struct proc *p;
186
187 if (watchdog_cpu != cpuid)
188 return;
189
190 printf("watchdog started on cpu %d\n", cpuid);
191 p = curproc;
192 bcopy(p->p_comm, old_pcomm, MAXCOMLEN + 1);
193 snprintf(p->p_comm, MAXCOMLEN + 1, "mp_watchdog cpu %d", cpuid);
194 while (1) {
195 DELAY(1000000); /* One second. */
196 if (watchdog_cpu != cpuid)
197 break;
198 atomic_subtract_int(&watchdog_timer, 1);
199 if (watchdog_timer < 4)
200 printf("Watchdog timer: %d\n", watchdog_timer);
201 if (watchdog_timer == 0 && watchdog_dontfire == 0) {
202 printf("Watchdog firing!\n");
203 watchdog_dontfire = 1;
204 if (watchdog_nmi)
205 watchdog_ipi_nmi();
206 else
207 kdb_enter(KDB_WHY_WATCHDOG, "mp_watchdog");
208 }
209 }
210 bcopy(old_pcomm, p->p_comm, MAXCOMLEN + 1);
211 printf("watchdog stopped on cpu %d\n", cpuid);
212 }
213