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Diffstat (limited to 'qemu/docs/aio_notify_accept.promela')
| -rw-r--r-- | qemu/docs/aio_notify_accept.promela | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/qemu/docs/aio_notify_accept.promela b/qemu/docs/aio_notify_accept.promela new file mode 100644 index 000000000..9cef2c955 --- /dev/null +++ b/qemu/docs/aio_notify_accept.promela @@ -0,0 +1,152 @@ +/* + * This model describes the interaction between ctx->notified + * and ctx->notifier. + * + * Author: Paolo Bonzini <pbonzini@redhat.com> + * + * This file is in the public domain. If you really want a license, + * the WTFPL will do. + * + * To verify the buggy version: + * spin -a -DBUG1 docs/aio_notify_bug.promela + * gcc -O2 pan.c + * ./a.out -a -f + * (or -DBUG2) + * + * To verify the fixed version: + * spin -a docs/aio_notify_bug.promela + * gcc -O2 pan.c + * ./a.out -a -f + * + * Add -DCHECK_REQ to test an alternative invariant and the + * "notify_me" optimization. + */ + +int notify_me; +bool notified; +bool event; +bool req; +bool notifier_done; + +#ifdef CHECK_REQ +#define USE_NOTIFY_ME 1 +#else +#define USE_NOTIFY_ME 0 +#endif + +#ifdef BUG +#error Please define BUG1 or BUG2 instead. +#endif + +active proctype notifier() +{ + do + :: true -> { + req = 1; + if + :: !USE_NOTIFY_ME || notify_me -> +#if defined BUG1 + /* CHECK_REQ does not detect this bug! */ + notified = 1; + event = 1; +#elif defined BUG2 + if + :: !notified -> event = 1; + :: else -> skip; + fi; + notified = 1; +#else + event = 1; + notified = 1; +#endif + :: else -> skip; + fi + } + :: true -> break; + od; + notifier_done = 1; +} + +#define AIO_POLL \ + notify_me++; \ + if \ + :: !req -> { \ + if \ + :: event -> skip; \ + fi; \ + } \ + :: else -> skip; \ + fi; \ + notify_me--; \ + \ + atomic { old = notified; notified = 0; } \ + if \ + :: old -> event = 0; \ + :: else -> skip; \ + fi; \ + \ + req = 0; + +active proctype waiter() +{ + bool old; + + do + :: true -> AIO_POLL; + od; +} + +/* Same as waiter(), but disappears after a while. */ +active proctype temporary_waiter() +{ + bool old; + + do + :: true -> AIO_POLL; + :: true -> break; + od; +} + +#ifdef CHECK_REQ +never { + do + :: req -> goto accept_if_req_not_eventually_false; + :: true -> skip; + od; + +accept_if_req_not_eventually_false: + if + :: req -> goto accept_if_req_not_eventually_false; + fi; + assert(0); +} + +#else +/* There must be infinitely many transitions of event as long + * as the notifier does not exit. + * + * If event stayed always true, the waiters would be busy looping. + * If event stayed always false, the waiters would be sleeping + * forever. + */ +never { + do + :: !event -> goto accept_if_event_not_eventually_true; + :: event -> goto accept_if_event_not_eventually_false; + :: true -> skip; + od; + +accept_if_event_not_eventually_true: + if + :: !event && notifier_done -> do :: true -> skip; od; + :: !event && !notifier_done -> goto accept_if_event_not_eventually_true; + fi; + assert(0); + +accept_if_event_not_eventually_false: + if + :: event -> goto accept_if_event_not_eventually_false; + fi; + assert(0); +} +#endif |