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

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=176c88f5214d8107d330971cbbfbbba5186a111f

commit 176c88f5214d8107d330971cbbfbbba5186a111f
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Oct 1 18:16:41 2021 +0200

    support: Add check for TID zero in support_wait_for_thread_exit
    
    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/>
    
    Fixes commit 032d74eaf6179100048a5bf0ce942e97dc8b9a60 ("support: Add
    support_wait_for_thread_exit").
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>
    Tested-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 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);