a.patch

commit f32f2770642109b85fadabd855ce064f42f710ed (HEAD -> master)
Author: Sultan Alsawaf <sultan@openresty.com>
Date:   Thu Oct 29 01:20:31 2020 -0700

    task_finder: error out when we cannot attach to _stp_target

    In order to avoid sleeping, stap_find_exe_file() does a trylock attempt
    on an mm's mmap semaphore and returns NULL when the lock is contented.
    When this happens, it can cause the task finder to not attach to a
    desired target process. This is especially noticeable when a target PID
    is specified, in which case the target PID itself can get skipped over
    by the task finder.

    Therefore, we should treat failures to get the exe file for a specific
    target PID as fatal, since that means the target PID will never get
    attached. Note that we must return a negative value from
    stap_start_task_finder() in order for the fatal error to be honored, so
    we shouldn't negate PTR_ERR(mmpath).

    Signed-off-by: Yichun Zhang (agentzh) <yichun@openresty.com>

diff --git a/po/en.gmo b/po/en.gmo
index 1f3bb4290..16c56b0dc 100644
Binary files a/po/en.gmo and b/po/en.gmo differ
diff --git a/po/fr.gmo b/po/fr.gmo
index 3daa003f5..6d4df7307 100644
Binary files a/po/fr.gmo and b/po/fr.gmo differ
diff --git a/runtime/linux/task_finder.c b/runtime/linux/task_finder.c
index 62a872624..8b95f3e1a 100644
--- a/runtime/linux/task_finder.c
+++ b/runtime/linux/task_finder.c
@@ -1684,8 +1684,11 @@ stap_start_task_finder(void)
                mmpath = __stp_get_mm_path(tsk->mm, mmpath_buf, PATH_MAX);
                task_unlock(tsk);
                if (mmpath == NULL || IS_ERR(mmpath)) {
-                       rc = -PTR_ERR(mmpath);
-                       if (rc == ENOENT) {
+                       rc = PTR_ERR(mmpath);
+                       /* If this was our target then it's a fatal error */
+                       if (!_stp_target && rc == -ENOENT) {
+                               _stp_warn("Unable to get path (error %d) for pid %d",
+                                          rc, (int)tsk->pid);
                                rc = 0; /* ignore ENOENT */
                                continue;
                        }
diff --git a/runtime/linux/task_finder2.c b/runtime/linux/task_finder2.c
index 8b8057a0e..93b7e2131 100644
--- a/runtime/linux/task_finder2.c
+++ b/runtime/linux/task_finder2.c
@@ -1803,8 +1803,11 @@ stap_start_task_finder(void)
                mmpath = __stp_get_mm_path(tsk->mm, mmpath_buf, PATH_MAX);
                task_unlock(tsk);
                if (mmpath == NULL || IS_ERR(mmpath)) {
-                       rc = -PTR_ERR(mmpath);
-                       if (rc == ENOENT) {
+                       rc = PTR_ERR(mmpath);
+                       /* If this was our target then it's a fatal error */
+                       if (!_stp_target && rc == -ENOENT) {
+                               _stp_warn("Unable to get path (error %d) for pid %d",
+                                          rc, (int)tsk->pid);
                                rc = 0; /* ignore ENOENT */
                                continue;
                        }