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misc/tst-clone3: Fix waiting for exited thread.

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From time to time the test misc/tst-clone3 fails with a timeout.
Then futex_wait is blocking.  Usually ctid should be set to zero
due to CLONE_CHILD_CLEARTID and the futex should be waken up.
But the fail occures if the thread has already exited before
ctid is set to the return value of clone().  Then futex_wait() will
block as there will be nobody who wakes the futex up again.

This patch initializes ctid to a known value before calling clone
and the kernel is the only one who updates the value to zero after clone.
If futex_wait is called then it is either waked up due to the exited thread
or the futex syscall fails as *ctid_ptr is already zero instead of the
specified value 1.

ChangeLog:

	* sysdeps/unix/sysv/linux/tst-clone3.c (do_test):
	Initialize ctid with a known value and remove update of ctid
	after clone.
	(wait_tid): Adjust arguments and call futex_wait with ctid_val
	as assumed current value of ctid_ptr.
This commit is contained in:
Stefan Liebler 2019-02-18 16:12:01 +01:00
parent ad18dadec9
commit 6c29942cbf
2 changed files with 23 additions and 8 deletions
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8
ChangeLog
View File

@ -1,3 +1,11 @@
2019-02-18 Stefan Liebler <stli@linux.ibm.com>
* sysdeps/unix/sysv/linux/tst-clone3.c (do_test):
Initialize ctid with a known value and remove update of ctid
after clone.
(wait_tid): Adjust arguments and call futex_wait with ctid_val
as assumed current value of ctid_ptr.
2019-02-15 Florian Weimer <fweimer@redhat.com>
Check that non-sysdeps headers have wrapper headers.

23
sysdeps/unix/sysv/linux/tst-clone3.c
View File

@ -27,6 +27,7 @@
#include <stackinfo.h> /* For _STACK_GROWS_{UP,DOWN}. */
#include <support/check.h>
#include <stdatomic.h>
/* Test if clone call with CLONE_THREAD does not call exit_group. The 'f'
function returns '1', which will be used by clone thread to call the
@ -42,11 +43,14 @@ f (void *a)
/* Futex wait for TID argument, similar to pthread_join internal
implementation. */
#define wait_tid(tid) \
do { \
__typeof (tid) __tid; \
while ((__tid = (tid)) != 0) \
futex_wait (&(tid), __tid); \
#define wait_tid(ctid_ptr, ctid_val) \
do { \
__typeof (*(ctid_ptr)) __tid; \
/* We need acquire MO here so that we synchronize with the \
kernel's store to 0 when the clone terminates. */ \
while ((__tid = atomic_load_explicit (ctid_ptr, \
memory_order_acquire)) != 0) \
futex_wait (ctid_ptr, ctid_val); \
} while (0)
static inline int
@ -64,7 +68,11 @@ do_test (void)
clone_flags |= CLONE_VM | CLONE_SIGHAND;
/* We will used ctid to call on futex to wait for thread exit. */
clone_flags |= CLONE_CHILD_CLEARTID;
pid_t ctid, tid;
/* Initialize with a known value. ctid is set to zero by the kernel after the
cloned thread has exited. */
#define CTID_INIT_VAL 1
pid_t ctid = CTID_INIT_VAL;
pid_t tid;
#ifdef __ia64__
extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base,
@ -86,8 +94,7 @@ do_test (void)
if (tid == -1)
FAIL_EXIT1 ("clone failed: %m");
ctid = tid;
wait_tid (ctid);
wait_tid (&ctid, CTID_INIT_VAL);
return 2;
}