Messages in this thread Patch in this message | | | Date | Mon, 5 Mar 2012 12:11:44 +0400 | From | Cyrill Gorcunov <> | Subject | [RFC] c/r: prctl: Add ability to get clear_tid_address |
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Hi guys,
there were a converation about ability to retrieve task::clear_tid_address (https://lkml.org/lkml/2012/2/3/116) via ptrace call, which was found as being a bit inappropriate. So we've switched to prctl interface instead. What do you think? Did I miss something? Comments are welcome
Cyrill --- Subject: [RFC] c/r: prctl: Add ability to get clear_tid_address
From: Andrew Vagin <avagin@openvz.org>
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 <avagin@openvz.org> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> CC: Pedro Alves <palves@redhat.com> CC: Oleg Nesterov <oleg@redhat.com> CC: Pavel Emelyanov <xemul@parallels.com> CC: Tejun Heo <tj@kernel.org> --- 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 @@ -1903,12 +1903,22 @@ 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, 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, @@ -2063,6 +2073,9 @@ 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;
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