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commit 6c29942cbf059aca47fd4bbd852ea42c9d46b71f
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Author: Stefan Liebler <stli@linux.ibm.com>
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Date: Mon Feb 18 16:12:01 2019 +0100
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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.
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Then futex_wait is blocking. Usually ctid should be set to zero
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due to CLONE_CHILD_CLEARTID and the futex should be waken up.
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But the fail occures if the thread has already exited before
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ctid is set to the return value of clone(). Then futex_wait() will
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block as there will be nobody who wakes the futex up again.
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This patch initializes ctid to a known value before calling clone
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and the kernel is the only one who updates the value to zero after clone.
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If futex_wait is called then it is either waked up due to the exited thread
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or the futex syscall fails as *ctid_ptr is already zero instead of the
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specified value 1.
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ChangeLog:
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* sysdeps/unix/sysv/linux/tst-clone3.c (do_test):
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Initialize ctid with a known value and remove update of ctid
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after clone.
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(wait_tid): Adjust arguments and call futex_wait with ctid_val
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as assumed current value of ctid_ptr.
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diff --git a/sysdeps/unix/sysv/linux/tst-clone3.c b/sysdeps/unix/sysv/linux/tst-clone3.c
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index 784ce18f5343ec72..9f1ed6355e7acffd 100644
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--- a/sysdeps/unix/sysv/linux/tst-clone3.c
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+++ b/sysdeps/unix/sysv/linux/tst-clone3.c
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@@ -27,6 +27,7 @@
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#include <stackinfo.h> /* For _STACK_GROWS_{UP,DOWN}. */
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#include <support/check.h>
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+#include <stdatomic.h>
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/* Test if clone call with CLONE_THREAD does not call exit_group. The 'f'
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function returns '1', which will be used by clone thread to call the
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@@ -42,11 +43,14 @@ f (void *a)
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/* Futex wait for TID argument, similar to pthread_join internal
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implementation. */
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-#define wait_tid(tid) \
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- do { \
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- __typeof (tid) __tid; \
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- while ((__tid = (tid)) != 0) \
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- futex_wait (&(tid), __tid); \
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+#define wait_tid(ctid_ptr, ctid_val) \
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+ do { \
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+ __typeof (*(ctid_ptr)) __tid; \
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+ /* We need acquire MO here so that we synchronize with the \
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+ kernel's store to 0 when the clone terminates. */ \
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+ while ((__tid = atomic_load_explicit (ctid_ptr, \
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+ memory_order_acquire)) != 0) \
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+ futex_wait (ctid_ptr, ctid_val); \
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} while (0)
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static inline int
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@@ -64,7 +68,11 @@ do_test (void)
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clone_flags |= CLONE_VM | CLONE_SIGHAND;
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/* We will used ctid to call on futex to wait for thread exit. */
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clone_flags |= CLONE_CHILD_CLEARTID;
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- pid_t ctid, tid;
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+ /* Initialize with a known value. ctid is set to zero by the kernel after the
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+ cloned thread has exited. */
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+#define CTID_INIT_VAL 1
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+ pid_t ctid = CTID_INIT_VAL;
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+ pid_t tid;
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#ifdef __ia64__
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extern int __clone2 (int (*__fn) (void *__arg), void *__child_stack_base,
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@@ -86,8 +94,7 @@ do_test (void)
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if (tid == -1)
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FAIL_EXIT1 ("clone failed: %m");
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- ctid = tid;
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- wait_tid (ctid);
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+ wait_tid (&ctid, CTID_INIT_VAL);
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return 2;
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}
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