[DTrace-devel] [PATCH 2/2] EINTR: make safe under signal hits

[Nick Alcock]

This commit audits DTrace (especially libproc and dt_proc, but not only
that) for syscalls and library calls that may return EINTR but are not
suitably guarded, and guards them.  (The plan was also to have any of them
that needed to actually *use* this EINTR to trigger an early return to do
that as well, but it turns out that none do, not even the ones in libproc.)

This matters for libproc and dt_proc in particular now because the monitor
thread is routinely hit by signals and so has to expect EINTR returns from
appropriate syscalls (and consider what to do if that happens, because it
means a proxy request is waiting and the DTrace main thread is blocked on
it).

Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
---
 libcommon/dof_parser_host.c | 6 ++++--
 libdtrace/dt_consume.c      | 9 ++++++---
 libdtrace/dt_pcap.c         | 5 +++--
 libdtrace/dt_proc.c         | 2 +-
 libproc/Pcontrol.c          | 2 +-
 libproc/elfish.c            | 5 +++--
 6 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/libcommon/dof_parser_host.c b/libcommon/dof_parser_host.c
index feb719020dc18..5c6db673fe810 100644
--- a/libcommon/dof_parser_host.c
+++ b/libcommon/dof_parser_host.c
@@ -92,10 +92,12 @@ dof_parser_host_read(int in, int timeout)
 	for (i = 0, sz = offsetof(dof_parsed_t, type); i < sz;) {
 		size_t ret;
 
-		if ((ret = poll(&fd, 1, timeout * 1000)) <= 0)
+		while ((ret = poll(&fd, 1, timeout * 1000)) <= 0 && errno == EINTR);
+		if (ret < 0)
 			goto err;
 
-		ret = read(in, ((char *) reply) + i, sz - i);
+		while ((ret = read(in, ((char *) reply) + i, sz - i)) < 0 &&
+		       errno == EINTR);
 
 		if (ret <= 0)
 			goto err;
diff --git a/libdtrace/dt_consume.c b/libdtrace/dt_consume.c
index f5dfc373caea7..e25f6759b7270 100644
--- a/libdtrace/dt_consume.c
+++ b/libdtrace/dt_consume.c
@@ -3065,9 +3065,12 @@ dtrace_consume(dtrace_hdl_t *dtp, FILE *fp, dtrace_consume_probe_f *pf,
 	 * We therefore need to convert the value.
 	 */
 	interval /= NANOSEC / MILLISEC;
-	cnt = epoll_wait(dtp->dt_poll_fd, events, dtp->dt_conf.num_online_cpus,
-			 interval);
-	if (cnt < 0) {
+
+	while ((cnt = epoll_wait(dtp->dt_poll_fd, events,
+				 dtp->dt_conf.num_online_cpus, interval)) < 0 &&
+	       errno == EINTR);
+
+        if (cnt < 0) {
 		dt_set_errno(dtp, errno);
 		return DTRACE_WORKSTATUS_ERROR;
 	}
diff --git a/libdtrace/dt_pcap.c b/libdtrace/dt_pcap.c
index 484816deccacc..bb41759eb8226 100644
--- a/libdtrace/dt_pcap.c
+++ b/libdtrace/dt_pcap.c
@@ -98,7 +98,8 @@ dt_pcap_destroy(dtrace_hdl_t *dtp)
 		 */
 		close(dtp->dt_pcap.dt_pcap_pipe[1]);
 		pthread_join(dtp->dt_pcap.dt_pcap_output, NULL);
-		waitpid(dtp->dt_pcap.dt_pcap_pid, NULL, 0);
+		while (waitpid(dtp->dt_pcap.dt_pcap_pid, NULL, 0) < 0 &&
+		       errno == EINTR);
 	}
 }
 
@@ -368,7 +369,7 @@ dt_pcap_filename(dtrace_hdl_t *dtp, FILE *fp)
 			 */
 			close(pipe_in[1]);
 			close(pipe_out[0]);
-			waitpid(pid, NULL, 0);
+			while (waitpid(pid, NULL, 0) < 0 && errno == EINTR);
 			dtp->dt_pcap.dt_pcap_pid = -1;
 			return NULL;
 	}
diff --git a/libdtrace/dt_proc.c b/libdtrace/dt_proc.c
index ed142c3bfd46f..64d0a763cd56d 100644
--- a/libdtrace/dt_proc.c
+++ b/libdtrace/dt_proc.c
@@ -1138,7 +1138,7 @@ dt_proc_loop(dt_proc_t *dpr, int awaiting_continue)
 			jmp_buf this_exec_jmp, *old_exec_jmp;
 			volatile int did_exec_retry = 0;
 
-			read(dpr->dpr_proxy_fd[0], &junk, 1);
+			while (read(dpr->dpr_proxy_fd[0], &junk, 1) < 0 && errno == EINTR);
 			pfd.revents = 0;
 
 			/*
diff --git a/libproc/Pcontrol.c b/libproc/Pcontrol.c
index 0cc1692f3b489..eb450bdc29814 100644
--- a/libproc/Pcontrol.c
+++ b/libproc/Pcontrol.c
@@ -211,7 +211,7 @@ Pcreate(
 	}
 	close(forkblock[1]);
 
-	waitpid(pid, &status, 0);
+	while (waitpid(pid, &status, 0) < 0 && errno == EINTR);
 	if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGTRAP ||
 	    (status >> 8) != (SIGTRAP | PTRACE_EVENT_EXEC << 8)) {
 		rc = ENOENT;
diff --git a/libproc/elfish.c b/libproc/elfish.c
index f4e54e8324001..210e5ff0f5db5 100644
--- a/libproc/elfish.c
+++ b/libproc/elfish.c
@@ -35,7 +35,7 @@
 int
 Pread_isa_info(struct ps_prochandle *P, const char *procname)
 {
-	int fd;
+	int fd, err;
 	Elf64_Ehdr hdr;
 
 	if ((fd = open(procname, O_RDONLY)) < 0) {
@@ -43,7 +43,8 @@ Pread_isa_info(struct ps_prochandle *P, const char *procname)
 		return -1;
 	}
 
-	if (read(fd, &hdr, sizeof(hdr)) < 0) {
+	while ((err = read(fd, &hdr, sizeof(hdr))) < 0 && errno == EINTR);
+        if (err < 0) {
 		_dprintf("%s is not an ELF file\n", procname);
 		close(fd);
 		return -1;
-- 
2.42.0.271.g85384428f1