Zero is written at clear_tid_address, when the process exits. This functionality is used by pthread_join(). We already have sys_set_tid_address() to change this address for current task but there is no way to obtain it from a user space. Without ability to find this address and dump it we can't restore pthread'ed apps which do call pthread_join() once they have been restored. This patch introduces PR_GET_TID_ADDRESS prctl option which allow current process to obtain own clear_tid_address. This feature is available iif CONFIG_CHECKPOINT_RESTORE is set. Signed-off-by: Andrew Vagin Signed-off-by: Cyrill Gorcunov CC: Pedro Alves CC: Oleg Nesterov CC: Pavel Emelyanov CC: Tejun Heo --- include/linux/prctl.h | 2 ++ kernel/sys.c | 13 +++++++++++++ 2 files changed, 15 insertions(+) Index: linux-2.6.git/include/linux/prctl.h =================================================================== --- linux-2.6.git.orig/include/linux/prctl.h +++ linux-2.6.git/include/linux/prctl.h @@ -120,4 +120,6 @@ # define PR_SET_MM_AUXV 12 # define PR_SET_MM_EXE_FILE 13 +#define PR_GET_TID_ADDRESS 36 + #endif /* _LINUX_PRCTL_H */ Index: linux-2.6.git/kernel/sys.c =================================================================== --- linux-2.6.git.orig/kernel/sys.c +++ linux-2.6.git/kernel/sys.c @@ -1897,12 +1897,22 @@ out: up_read(&mm->mmap_sem); return error; } + +static int prctl_get_tid_address(struct task_struct *me, int __user **tid_addr) +{ + return put_user(me->clear_child_tid, tid_addr); +} + #else /* CONFIG_CHECKPOINT_RESTORE */ static int prctl_set_mm(int opt, unsigned long addr, unsigned long arg4, unsigned long arg5) { return -EINVAL; } +static int prctl_get_tid_address(struct task_struct *me, int __user **tid_addr) +{ + return -EINVAL; +} #endif SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, @@ -2057,6 +2067,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsi case PR_SET_MM: error = prctl_set_mm(arg2, arg3, arg4, arg5); break; + case PR_GET_TID_ADDRESS: + error = prctl_get_tid_address(me, (int __user **)arg2); + break; default: error = -EINVAL; break; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/