1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3  * Test that poll handlers are not re-entrant in nested aio_poll()
4  *
5  * Copyright Red Hat
6  *
7  * Poll handlers are usually level-triggered. That means they continue firing
8  * until the condition is reset (e.g. a virtqueue becomes empty). If a poll
9  * handler calls nested aio_poll() before the condition is reset, then infinite
10  * recursion occurs.
11  *
12  * aio_poll() is supposed to prevent this by disabling poll handlers in nested
13  * aio_poll() calls. This test case checks that this is indeed what happens.
14  */
15 #include "qemu/osdep.h"
16 #include "block/aio.h"
17 #include "qapi/error.h"
18 
19 typedef struct {
20     AioContext *ctx;
21 
22     /* This is the EventNotifier that drives the test */
23     EventNotifier poll_notifier;
24 
25     /* This EventNotifier is only used to wake aio_poll() */
26     EventNotifier dummy_notifier;
27 
28     bool nested;
29 } TestData;
30 
31 static void io_read(EventNotifier *notifier)
32 {
33     event_notifier_test_and_clear(notifier);
34 }
35 
36 static bool io_poll_true(void *opaque)
37 {
38     return true;
39 }
40 
41 static bool io_poll_false(void *opaque)
42 {
43     return false;
44 }
45 
46 static void io_poll_ready(EventNotifier *notifier)
47 {
48     TestData *td = container_of(notifier, TestData, poll_notifier);
49 
50     g_assert(!td->nested);
51     td->nested = true;
52 
53     /* Wake the following nested aio_poll() call */
54     event_notifier_set(&td->dummy_notifier);
55 
56     /* This nested event loop must not call io_poll()/io_poll_ready() */
57     g_assert(aio_poll(td->ctx, true));
58 
59     td->nested = false;
60 }
61 
62 /* dummy_notifier never triggers */
63 static void io_poll_never_ready(EventNotifier *notifier)
64 {
65     g_assert_not_reached();
66 }
67 
68 static void test(void)
69 {
70     TestData td = {
71         .ctx = aio_context_new(&error_abort),
72     };
73 
74     qemu_set_current_aio_context(td.ctx);
75 
76     /* Enable polling */
77     aio_context_set_poll_params(td.ctx, 1000000, 2, 2, &error_abort);
78 
79     /*
80      * The GSource is unused but this has the side-effect of changing the fdmon
81      * that AioContext uses.
82      */
83     aio_get_g_source(td.ctx);
84 
85     /* Make the event notifier active (set) right away */
86     event_notifier_init(&td.poll_notifier, 1);
87     aio_set_event_notifier(td.ctx, &td.poll_notifier,
88                            io_read, io_poll_true, io_poll_ready);
89 
90     /* This event notifier will be used later */
91     event_notifier_init(&td.dummy_notifier, 0);
92     aio_set_event_notifier(td.ctx, &td.dummy_notifier,
93                            io_read, io_poll_false, io_poll_never_ready);
94 
95     /* Consume aio_notify() */
96     g_assert(!aio_poll(td.ctx, false));
97 
98     /*
99      * Run the io_read() handler. This has the side-effect of activating
100      * polling in future aio_poll() calls.
101      */
102     g_assert(aio_poll(td.ctx, true));
103 
104     /* The second time around the io_poll()/io_poll_ready() handler runs */
105     g_assert(aio_poll(td.ctx, true));
106 
107     /* Run io_poll()/io_poll_ready() one more time to show it keeps working */
108     g_assert(aio_poll(td.ctx, true));
109 
110     aio_set_event_notifier(td.ctx, &td.dummy_notifier, NULL, NULL, NULL);
111     aio_set_event_notifier(td.ctx, &td.poll_notifier, NULL, NULL, NULL);
112     event_notifier_cleanup(&td.dummy_notifier);
113     event_notifier_cleanup(&td.poll_notifier);
114     aio_context_unref(td.ctx);
115 }
116 
117 int main(int argc, char **argv)
118 {
119     g_test_init(&argc, &argv, NULL);
120     g_test_add_func("/nested-aio-poll", test);
121     return g_test_run();
122 }
123