From eb76e5b465a4b7b569cde4b4f57d1fcb4695c1c6 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Tue, 12 Feb 2019 12:36:46 -0200 Subject: nptl: Reinstate pthread_timedjoin_np as a cancellation point (BZ#24215) Patch ce7eb0e90315 ("nptl: Cleanup cancellation macros") changed the join sequence for internal common __pthread_timedjoin_ex to use the new macro lll_wait_tid. The idea was this macro would issue the cancellable futex operation depending whether the timeout is used or not. However if a timeout is used, __lll_timedwait_tid is called and it is not a cancellable entrypoint. This patch fixes it by simplifying the code in various ways: - Instead of adding the cancellation handling on __lll_timedwait_tid, it moves the generic implementation to pthread_join_common.c (called now timedwait_tid with some fixes to use the correct type for pid). - The llvm_wait_tid macro is removed, along with its replication on x86_64, i686, and sparc arch-specific lowlevellock.h. - sparc32 __lll_timedwait_tid is also removed, since the code is similar to generic one. - x86_64 and i386 provides arch-specific __lll_timedwait_tid which is also removed since they are similar in functionality to generic C code and there is no indication it is better than compiler generated code. New tests, tst-join8 and tst-join9, are provided to check if pthread_timedjoin_np acts as a cancellation point. Checked on x86_64-linux-gnu, i686-linux-gnu, sparcv9-linux-gnu, and aarch64-linux-gnu. [BZ #24215] * nptl/Makefile (lpthread-routines): Remove lll_timedwait_tid. (tests): Add tst-join8 tst-join9. * nptl/lll_timedwait_tid.c: Remove file. * sysdeps/sparc/sparc32/lll_timedwait_tid.c: Likewise. * sysdeps/unix/sysv/linux/i386/lll_timedwait_tid.c: Likewise. * sysdeps/sysv/linux/x86_64/lll_timedwait_tid.c: Likewise. * nptl/pthread_join_common.c (timedwait_tid): New function. (__pthread_timedjoin_ex): Act as cancellation entrypoint is block is set. * nptl/tst-join5.c (thread_join): New function. (tf1, tf2, do_test): Use libsupport and add pthread_timedjoin_np check. * nptl/tst-join8.c: New file. * nptl/tst-join9.c: Likewise. * sysdeps/nptl/lowlevellock-futex.h (lll_futex_wait_cancel, lll_futex_timed_wait_cancel): Add generic macros. * sysdeps/nptl/lowlevellock.h (__lll_timedwait_tid, lll_wait_tid): Remove definitions. * sysdeps/unix/sysv/linux/i386/lowlevellock.h: Likewise. * sysdeps/unix/sysv/linux/sparc/lowlevellock.h: Likewise. * sysdeps/unix/sysv/linux/x86_64/lowlevellock.h: Likewise. * sysdeps/sparc/sparc32/lowlevellock.c (__lll_timedwait_tid): Remove function. * sysdeps/unix/sysv/linux/i386/lowlevellock.S (__lll_timedwait_tid): Likewise. * sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: Likewise. * sysdeps/unix/sysv/linux/lowlevellock-futex.h (lll_futex_timed_wait_cancel): New macro. --- nptl/pthread_join_common.c | 61 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 60 insertions(+), 1 deletion(-) (limited to 'nptl/pthread_join_common.c') diff --git a/nptl/pthread_join_common.c b/nptl/pthread_join_common.c index ecb78ffba5..6efe8efc3f 100644 --- a/nptl/pthread_join_common.c +++ b/nptl/pthread_join_common.c @@ -30,6 +30,52 @@ cleanup (void *arg) atomic_compare_exchange_weak_acquire (&arg, &self, NULL); } +/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex + wake-up when the clone terminates. The memory location contains the + thread ID while the clone is running and is reset to zero by the kernel + afterwards. The kernel up to version 3.16.3 does not use the private futex + operations for futex wake-up when the clone terminates. */ +static int +timedwait_tid (pid_t *tidp, const struct timespec *abstime) +{ + pid_t tid; + + if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000) + return EINVAL; + + /* Repeat until thread terminated. */ + while ((tid = *tidp) != 0) + { + struct timeval tv; + struct timespec rt; + + /* Get the current time. */ + __gettimeofday (&tv, NULL); + + /* Compute relative timeout. */ + rt.tv_sec = abstime->tv_sec - tv.tv_sec; + rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000; + if (rt.tv_nsec < 0) + { + rt.tv_nsec += 1000000000; + --rt.tv_sec; + } + + /* Already timed out? */ + if (rt.tv_sec < 0) + return ETIMEDOUT; + + /* If *tidp == tid, wait until thread terminates or the wait times out. + The kernel up to version 3.16.3 does not use the private futex + operations for futex wake-up when the clone terminates. */ + if (lll_futex_timed_wait_cancel (tidp, tid, &rt, LLL_SHARED) + == -ETIMEDOUT) + return ETIMEDOUT; + } + + return 0; +} + int __pthread_timedjoin_ex (pthread_t threadid, void **thread_return, const struct timespec *abstime, bool block) @@ -74,6 +120,10 @@ __pthread_timedjoin_ex (pthread_t threadid, void **thread_return, /* There is already somebody waiting for the thread. */ return EINVAL; + /* BLOCK waits either indefinitely or based on an absolute time. POSIX also + states a cancellation point shall occur for pthread_join, and we use the + same rationale for posix_timedjoin_np. Both timedwait_tid and the futex + call use the cancellable variant. */ if (block) { /* During the wait we change to asynchronous cancellation. If we @@ -81,7 +131,16 @@ __pthread_timedjoin_ex (pthread_t threadid, void **thread_return, un-wait-ed for again. */ pthread_cleanup_push (cleanup, &pd->joinid); - result = lll_wait_tid (pd->tid, abstime); + if (abstime != NULL) + result = timedwait_tid (&pd->tid, abstime); + else + { + pid_t tid; + /* We need acquire MO here so that we synchronize with the + kernel's store to 0 when the clone terminates. (see above) */ + while ((tid = atomic_load_acquire (&pd->tid)) != 0) + lll_futex_wait_cancel (&pd->tid, tid, LLL_SHARED); + } pthread_cleanup_pop (0); } -- cgit 1.4.1