[PATCH] support: Add check for TID zero in support_wait_for_thread_exit

[Florian Weimer]

Some kernel versions (observed with kernel 5.14 and earlier) can list
"0" entries in /proc/self/task.  This happens when a thread exits
while the task list is being constructed.  Treat this entry as not
present, like the proposed kernel patch does:

[PATCH] procfs: Do not list TID 0 in /proc/<pid>/task
<https://lore.kernel.org/all/8735pn5dx7.fsf@oldenburg.str.redhat.com/>

---
 support/support_wait_for_thread_exit.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/support/support_wait_for_thread_exit.c b/support/support_wait_for_thread_exit.c
index 658a813810..5e3be421a7 100644
--- a/support/support_wait_for_thread_exit.c
+++ b/support/support_wait_for_thread_exit.c
@@ -43,7 +43,10 @@ support_wait_for_thread_exit (void)
           return;
         }
 
-      if (strcmp (e->d_name, ".") == 0 || strcmp (e->d_name, "..") == 0)
+      /* In some kernels, "0" entries denote a thread that has just
+         exited.  */
+      if (strcmp (e->d_name, ".") == 0 || strcmp (e->d_name, "..") == 0
+          || strcmp (e->d_name, "0") == 0)
         continue;
 
       int task_tid = atoi (e->d_name);