support: Add check for TID zero in support_wait_for_thread_exit

Message ID 878rze4690.fsf@oldenburg.str.redhat.com
State New
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Series
  • support: Add check for TID zero in support_wait_for_thread_exit
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Commit Message

Noah Goldstein via Libc-alpha Sept. 30, 2021, 12:06 p.m.
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(-)

Comments

Noah Goldstein via Libc-alpha Oct. 1, 2021, 3:27 p.m. | #1
On 9/30/21 08:06, Florian Weimer via Libc-alpha wrote:
> 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/>


Upstream kernel patch has been ack by Christian Brauner.

Testing looks good on x86_64 and i686. Patchwork CI/CD is clean 2/2.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Tested-by: Carlos O'Donell <carlos@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)


OK. Skip "0" entry.

>          continue;

>  

>        int task_tid = atoi (e->d_name);

> 



-- 
Cheers,
Carlos.

Patch

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);