*/
#include <urcu/compiler.h>
+#include <signal.h>
+#include <pthread.h>
#include <lttng/ringbuffer-config.h>
#include "backend_types.h"
* The subbuffer size is least 2 bytes (minimum size: 1 page).
* This guarantees that old_commit_count + 1 != commit_count.
*/
+
+ /*
+ * Order prior updates to reserve count prior to the
+ * commit_cold cc_sb update.
+ */
+ cmm_smp_wmb();
if (caa_likely(v_cmpxchg(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
old_commit_count, old_commit_count + 1)
== old_commit_count)) {
/* End of exclusive subbuffer access */
v_set(config, &shmp_index(handle, buf->commit_cold, idx)->cc_sb,
commit_count);
+ /*
+ * Order later updates to reserve count after
+ * the commit cold cc_sb update.
+ */
+ cmm_smp_wmb();
lib_ring_buffer_vmcore_check_deliver(config, buf,
commit_count, idx, handle);
int wakeup_fd = shm_get_wakeup_fd(handle, &buf->self._ref);
if (wakeup_fd >= 0) {
- int ret;
+ sigset_t sigpipe_set, pending_set, old_set;
+ int ret, sigpipe_was_pending = 0;
+
/*
* Wake-up the other end by
* writing a null byte in the
* 2) check if there is data in
* the buffer.
* 3) wait on the pipe (poll).
+ *
+ * Discard the SIGPIPE from write(), not
+ * disturbing any SIGPIPE that might be
+ * already pending. If a bogus SIGPIPE
+ * is sent to the entire process
+ * concurrently by a malicious user, it
+ * may be simply discarded.
*/
+ ret = sigemptyset(&pending_set);
+ assert(!ret);
+ /*
+ * sigpending returns the mask
+ * of signals that are _both_
+ * blocked for the thread _and_
+ * pending for either the thread
+ * or the entire process.
+ */
+ ret = sigpending(&pending_set);
+ assert(!ret);
+ sigpipe_was_pending = sigismember(&pending_set, SIGPIPE);
+ /*
+ * If sigpipe was pending, it
+ * means it was already blocked,
+ * so no need to block it.
+ */
+ if (!sigpipe_was_pending) {
+ ret = sigemptyset(&sigpipe_set);
+ assert(!ret);
+ ret = sigaddset(&sigpipe_set, SIGPIPE);
+ assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &sigpipe_set, &old_set);
+ assert(!ret);
+ }
do {
ret = write(wakeup_fd, "", 1);
} while (ret == -1L && errno == EINTR);
+ if (ret == -1L && errno == EPIPE && !sigpipe_was_pending) {
+ struct timespec timeout = { 0, 0 };
+ do {
+ ret = sigtimedwait(&sigpipe_set, NULL,
+ &timeout);
+ } while (ret == -1L && errno == EINTR);
+ }
+ if (!sigpipe_was_pending) {
+ ret = pthread_sigmask(SIG_SETMASK, &old_set, NULL);
+ assert(!ret);
+ }
}
}
-
}
}
}