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c/r: prctl: Add ability to get clear_tid_address

RFC In review Cyrill Gorcunov 1 participant 2 messages Mar 5, 2012 – Mar 7, 2012

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Cyrill Gorcunov

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#0 lore raw

RFC 1/1 c/r: prctl: Add ability to get clear_tid_address

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 <[email protected]>

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 <[email protected]>
Signed-off-by Cyrill Gorcunov <[email protected]>
CC Pedro Alves <[email protected]>
CC Oleg Nesterov <[email protected]>
CC Pavel Emelyanov <[email protected]>
CC Tejun Heo <[email protected]>
---
 include/linux/prctl.h |    2 ++
 kernel/sys.c          |   13 +++++++++++++
 2 files changed, 15 insertions(+)
include/linux/prctl.h +2 -0
Index: 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 */
kernel/sys.c +13 -0
Index: 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;
author
#1 lore raw
Quoted 7 lines · Cyrill Gorcunov

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

This patch has a typo, so ignore it please. I'll resend it in another series.