From 7e2e6a5add901a2a74e65cadb1beebb05e9abaeb Mon Sep 17 00:00:00 2001
From: Adrian Szyndela <adrian.s@samsung.com>
Date: Tue, 13 Dec 2016 14:43:06 +0100
Subject: [PATCH] crash-stack: work around hanging up on 'D' processes

Processes in uninterruptible sleep state ('D' status in ps)
cannot be ptraced until they leave the state. To prevent
hanging up of crash-stack, we check the target process state.
If it is 'D', then we give up ptracing it, and instead
print the information from /proc/<pid>/wchan, /proc/<pid>/syscall
and /proc/<pid>/stack.

Change-Id: I82644051a5499c42db2a8e51a7af98693e8da363
---
 src/crash-stack/crash-stack.c | 72 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/src/crash-stack/crash-stack.c b/src/crash-stack/crash-stack.c
index ef1814c..694f26c 100644
--- a/src/crash-stack/crash-stack.c
+++ b/src/crash-stack/crash-stack.c
@@ -290,6 +290,65 @@ void __find_symbol_in_elf(ProcInfo *proc_info, Dwarf_Addr mapping_start)
 	close(fd);
 }
 
+static int __attachable(pid_t pid)
+{
+	/* read /proc/<pid>/stat */
+	char buf[20];
+	FILE *f;
+	char status;
+
+	snprintf(buf, sizeof(buf), "/proc/%d/stat", pid);
+
+	f = fopen(buf, "r");
+	if (NULL == f)
+		return -1;
+
+	/* check if status is D */
+	if (fscanf(f, "%*d %*s %c", &status) != 1)
+		return -1;
+
+	fclose(f);
+
+	return status != 'D';
+}
+
+static void __print_proc_file(pid_t pid, const char *name)
+{
+	char buf[1024];
+	FILE *f;
+	int r;
+
+	snprintf(buf, sizeof(buf), "/proc/%d/%s", pid, name);
+
+	fprintf(outputfile, "%s:\n", buf);
+
+	f = fopen(buf, "r");
+	if (NULL == f)
+	{
+		fprintf(errfile, "Failed to open %s: %m\n", buf);
+		return;
+	}
+
+	while ((r = fread(buf, 1, sizeof(buf), f)) > 0)
+	{
+		fwrite(buf, r, 1, outputfile);
+	}
+
+	fclose(f);
+
+	fprintf(outputfile, "\n");
+}
+
+static void __print_not_attachable_process_info(pid_t pid)
+{
+	fprintf(outputfile, "ERROR: can't attach to process %d - process is in uninterruptible sleep state\n", pid);
+	fprintf(outputfile, "Giving some /proc info instead:\n\n");
+	__print_proc_file(pid, "wchan");
+	fprintf(outputfile, "\n");
+	__print_proc_file(pid, "syscall");
+	__print_proc_file(pid, "stack");
+}
+
 /**
  * @brief Opens libdwfl for using with live process
  *
@@ -301,6 +360,19 @@ static Dwfl *__open_dwfl_with_pid(pid_t pid, pid_t tid)
 	int status;
 	pid_t stopped_pid;
 
+	status = __attachable(pid);
+	if (-1 == status)
+	{
+		fprintf(errfile, "failed to read /proc/%d/stat: %m\n", pid);
+		return NULL;
+	}
+
+	if (!status)
+	{
+		__print_not_attachable_process_info(pid);
+		return NULL;
+	}
+
 	if (ptrace(PTRACE_SEIZE, tid, NULL, PTRACE_O_TRACEEXIT) != 0) {
 		fprintf(errfile, "PTRACE_SEIZE failed on TID %d: %m\n", tid);
 		return NULL;
-- 
2.7.4