1 #include "pthread_impl.h"
2 #include <semaphore.h>
3 #include <string.h>
4
dummy_0(void)5 static void dummy_0(void)
6 {
7 }
8
9 weak_alias(dummy_0, __tl_lock);
10 weak_alias(dummy_0, __tl_unlock);
11
12 static int target_tid;
13 static void (*callback)(void *), *context;
14 static sem_t target_sem, caller_sem;
15
dummy(void * p)16 static void dummy(void *p)
17 {
18 }
19
handler(int sig)20 static void handler(int sig)
21 {
22 if (__pthread_self()->tid != target_tid) return;
23
24 int old_errno = errno;
25
26 /* Inform caller we have received signal and wait for
27 * the caller to let us make the callback. */
28 sem_post(&caller_sem);
29 sem_wait(&target_sem);
30
31 callback(context);
32
33 /* Inform caller we've complered the callback and wait
34 * for the caller to release us to return. */
35 sem_post(&caller_sem);
36 sem_wait(&target_sem);
37
38 /* Inform caller we are returning and state is destroyable. */
39 sem_post(&caller_sem);
40
41 errno = old_errno;
42 }
43
__synccall(void (* func)(void *),void * ctx)44 void __synccall(void (*func)(void *), void *ctx)
45 {
46 sigset_t oldmask;
47 int cs, i, r;
48 struct sigaction sa = { .sa_flags = SA_RESTART, .sa_handler = handler };
49 pthread_t self = __pthread_self(), td;
50 int count = 0;
51
52 /* Blocking signals in two steps, first only app-level signals
53 * before taking the lock, then all signals after taking the lock,
54 * is necessary to achieve AS-safety. Blocking them all first would
55 * deadlock if multiple threads called __synccall. Waiting to block
56 * any until after the lock would allow re-entry in the same thread
57 * with the lock already held. */
58 __block_app_sigs(&oldmask);
59 __tl_lock();
60 __block_all_sigs(0);
61 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
62
63 sem_init(&target_sem, 0, 0);
64 sem_init(&caller_sem, 0, 0);
65
66 if (!libc.threads_minus_1 || __syscall(SYS_gettid) != self->tid)
67 goto single_threaded;
68
69 callback = func;
70 context = ctx;
71
72 /* Block even implementation-internal signals, so that nothing
73 * interrupts the SIGSYNCCALL handlers. The main possible source
74 * of trouble is asynchronous cancellation. */
75 memset(&sa.sa_mask, -1, sizeof sa.sa_mask);
76 __libc_sigaction(SIGSYNCCALL, &sa, 0);
77
78
79 for (td=self->next; td!=self; td=td->next) {
80 target_tid = td->tid;
81 while ((r = -__syscall(SYS_tkill, td->tid, SIGSYNCCALL)) == EAGAIN);
82 if (r) {
83 /* If we failed to signal any thread, nop out the
84 * callback to abort the synccall and just release
85 * any threads already caught. */
86 callback = func = dummy;
87 break;
88 }
89 sem_wait(&caller_sem);
90 count++;
91 }
92 target_tid = 0;
93
94 /* Serialize execution of callback in caught threads, or just
95 * release them all if synccall is being aborted. */
96 for (i=0; i<count; i++) {
97 sem_post(&target_sem);
98 sem_wait(&caller_sem);
99 }
100
101 sa.sa_handler = SIG_IGN;
102 __libc_sigaction(SIGSYNCCALL, &sa, 0);
103
104 single_threaded:
105 func(ctx);
106
107 /* Only release the caught threads once all threads, including the
108 * caller, have returned from the callback function. */
109 for (i=0; i<count; i++)
110 sem_post(&target_sem);
111 for (i=0; i<count; i++)
112 sem_wait(&caller_sem);
113
114 sem_destroy(&caller_sem);
115 sem_destroy(&target_sem);
116
117 pthread_setcancelstate(cs, 0);
118 __tl_unlock();
119 __restore_sigs(&oldmask);
120 }
121