Paolo Bonzini | 05e514b | 2015-07-21 16:07:53 +0200 | [diff] [blame] | 1 | /* |
| 2 | * This model describes the interaction between ctx->notified |
| 3 | * and ctx->notifier. |
| 4 | * |
| 5 | * Author: Paolo Bonzini <pbonzini@redhat.com> |
| 6 | * |
| 7 | * This file is in the public domain. If you really want a license, |
| 8 | * the WTFPL will do. |
| 9 | * |
| 10 | * To verify the buggy version: |
| 11 | * spin -a -DBUG1 docs/aio_notify_bug.promela |
| 12 | * gcc -O2 pan.c |
| 13 | * ./a.out -a -f |
| 14 | * (or -DBUG2) |
| 15 | * |
| 16 | * To verify the fixed version: |
| 17 | * spin -a docs/aio_notify_bug.promela |
| 18 | * gcc -O2 pan.c |
| 19 | * ./a.out -a -f |
| 20 | * |
| 21 | * Add -DCHECK_REQ to test an alternative invariant and the |
| 22 | * "notify_me" optimization. |
| 23 | */ |
| 24 | |
| 25 | int notify_me; |
| 26 | bool notified; |
| 27 | bool event; |
| 28 | bool req; |
| 29 | bool notifier_done; |
| 30 | |
| 31 | #ifdef CHECK_REQ |
| 32 | #define USE_NOTIFY_ME 1 |
| 33 | #else |
| 34 | #define USE_NOTIFY_ME 0 |
| 35 | #endif |
| 36 | |
| 37 | #ifdef BUG |
| 38 | #error Please define BUG1 or BUG2 instead. |
| 39 | #endif |
| 40 | |
| 41 | active proctype notifier() |
| 42 | { |
| 43 | do |
| 44 | :: true -> { |
| 45 | req = 1; |
| 46 | if |
| 47 | :: !USE_NOTIFY_ME || notify_me -> |
| 48 | #if defined BUG1 |
| 49 | /* CHECK_REQ does not detect this bug! */ |
| 50 | notified = 1; |
| 51 | event = 1; |
| 52 | #elif defined BUG2 |
| 53 | if |
| 54 | :: !notified -> event = 1; |
| 55 | :: else -> skip; |
| 56 | fi; |
| 57 | notified = 1; |
| 58 | #else |
| 59 | event = 1; |
| 60 | notified = 1; |
| 61 | #endif |
| 62 | :: else -> skip; |
| 63 | fi |
| 64 | } |
| 65 | :: true -> break; |
| 66 | od; |
| 67 | notifier_done = 1; |
| 68 | } |
| 69 | |
| 70 | #define AIO_POLL \ |
| 71 | notify_me++; \ |
| 72 | if \ |
| 73 | :: !req -> { \ |
| 74 | if \ |
| 75 | :: event -> skip; \ |
| 76 | fi; \ |
| 77 | } \ |
| 78 | :: else -> skip; \ |
| 79 | fi; \ |
| 80 | notify_me--; \ |
| 81 | \ |
| 82 | atomic { old = notified; notified = 0; } \ |
| 83 | if \ |
| 84 | :: old -> event = 0; \ |
| 85 | :: else -> skip; \ |
| 86 | fi; \ |
| 87 | \ |
| 88 | req = 0; |
| 89 | |
| 90 | active proctype waiter() |
| 91 | { |
| 92 | bool old; |
| 93 | |
| 94 | do |
| 95 | :: true -> AIO_POLL; |
| 96 | od; |
| 97 | } |
| 98 | |
| 99 | /* Same as waiter(), but disappears after a while. */ |
| 100 | active proctype temporary_waiter() |
| 101 | { |
| 102 | bool old; |
| 103 | |
| 104 | do |
| 105 | :: true -> AIO_POLL; |
| 106 | :: true -> break; |
| 107 | od; |
| 108 | } |
| 109 | |
| 110 | #ifdef CHECK_REQ |
| 111 | never { |
| 112 | do |
| 113 | :: req -> goto accept_if_req_not_eventually_false; |
| 114 | :: true -> skip; |
| 115 | od; |
| 116 | |
| 117 | accept_if_req_not_eventually_false: |
| 118 | if |
| 119 | :: req -> goto accept_if_req_not_eventually_false; |
| 120 | fi; |
| 121 | assert(0); |
| 122 | } |
| 123 | |
| 124 | #else |
| 125 | /* There must be infinitely many transitions of event as long |
| 126 | * as the notifier does not exit. |
| 127 | * |
| 128 | * If event stayed always true, the waiters would be busy looping. |
| 129 | * If event stayed always false, the waiters would be sleeping |
| 130 | * forever. |
| 131 | */ |
| 132 | never { |
| 133 | do |
| 134 | :: !event -> goto accept_if_event_not_eventually_true; |
| 135 | :: event -> goto accept_if_event_not_eventually_false; |
| 136 | :: true -> skip; |
| 137 | od; |
| 138 | |
| 139 | accept_if_event_not_eventually_true: |
| 140 | if |
| 141 | :: !event && notifier_done -> do :: true -> skip; od; |
| 142 | :: !event && !notifier_done -> goto accept_if_event_not_eventually_true; |
| 143 | fi; |
| 144 | assert(0); |
| 145 | |
| 146 | accept_if_event_not_eventually_false: |
| 147 | if |
| 148 | :: event -> goto accept_if_event_not_eventually_false; |
| 149 | fi; |
| 150 | assert(0); |
| 151 | } |
| 152 | #endif |