[PATCH] nptl: Fix tst-cancel7 and tst-cancelx7 pidfile race

[PATCH] nptl: Fix tst-cancel7 and tst-cancelx7 pidfile race

[Stafford Horne via Libc-alpha]

The check for waiting for the pidfile to be created looks wrong.  At the
point when ACCESS is run the pid file will always be created and
accessible as it is created during DO_PREPARE.  This means that thread
cancellation may be performed before the pid is written to the pidfile.

This was found to be flaky when testing on my OpenRISC platform.

Fix this by using the semaphore to wait for pidfile pid write
completion.
---
 nptl/tst-cancel7.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/nptl/tst-cancel7.c b/nptl/tst-cancel7.c
index 54ed2a54ff..e926f4455c 100644
--- a/nptl/tst-cancel7.c
+++ b/nptl/tst-cancel7.c
@@ -115,16 +115,13 @@ do_test (void)
 {
   pthread_t th = xpthread_create (NULL, tf, NULL);
 
-  do
-    nanosleep (&(struct timespec) { .tv_sec = 0, .tv_nsec = 100000000 }, NULL);
-  while (access (pidfilename, R_OK) != 0);
+  /* Wait to cancel until after the pid is written.  */
+  if (sem_wait (sem) != 0)
+    FAIL_EXIT1 ("sem_wait: %m");
 
   xpthread_cancel (th);
   void *r = xpthread_join (th);
 
-  if (sem_wait (sem) != 0)
-    FAIL_EXIT1 ("sem_wait: %m");
-
   FILE *f = xfopen (pidfilename, "r+");
 
   long long ll;
-- 
2.31.1

Re: [PATCH] nptl: Fix tst-cancel7 and tst-cancelx7 pidfile race

[Adhemerval Zanella via Libc-alpha]

On 16/10/2021 19:41, Stafford Horne via Libc-alpha wrote:
> The check for waiting for the pidfile to be created looks wrong.  At the
> point when ACCESS is run the pid file will always be created and
> accessible as it is created during DO_PREPARE.  This means that thread
> cancellation may be performed before the pid is written to the pidfile.
> 
> This was found to be flaky when testing on my OpenRISC platform.
> 
> Fix this by using the semaphore to wait for pidfile pid write
> completion.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> ---
>  nptl/tst-cancel7.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/nptl/tst-cancel7.c b/nptl/tst-cancel7.c
> index 54ed2a54ff..e926f4455c 100644
> --- a/nptl/tst-cancel7.c
> +++ b/nptl/tst-cancel7.c
> @@ -115,16 +115,13 @@ do_test (void)
>  {
>    pthread_t th = xpthread_create (NULL, tf, NULL);
>  
> -  do
> -    nanosleep (&(struct timespec) { .tv_sec = 0, .tv_nsec = 100000000 }, NULL);
> -  while (access (pidfilename, R_OK) != 0);
> +  /* Wait to cancel until after the pid is written.  */
> +  if (sem_wait (sem) != 0)
> +    FAIL_EXIT1 ("sem_wait: %m");
>  
>    xpthread_cancel (th);
>    void *r = xpthread_join (th);
>  
> -  if (sem_wait (sem) != 0)
> -    FAIL_EXIT1 ("sem_wait: %m");
> -
>    FILE *f = xfopen (pidfilename, "r+");
>  
>    long long ll;
>