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authorEric W. Biederman <ebiederm@xmission.com>2006-06-23 05:05:18 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-23 10:43:03 -0400
commit260ea1013283d8acbb451459ed1ca560c1445c20 (patch)
tree35819d28dbfa8600ac0de336147323e660b0390c
parent4a4b69f79ba7286794765a856349e380f984a6cb (diff)
[PATCH] ptrace: document the locking rules
After a lot of reading the code and thinking about how it behaves I have managed to figure out what the current ptrace locking rules are. The current code is in much better that it appears at first glance. The troublesome code paths are actually the code paths that violate the current rules. ptrace uses simple exclusive access as it's locking. You can only touch task->ptrace if the task is stopped and you are the ptracer, or if the task is running and are the task itself. Very simple, very easy to maintain. It just needs to be documented so people know not to touch ptrace from elsewhere. Currently we do have a few pieces of code that are in violation of this rule. Particularly the core dump code, and ptrace_attach. But so far the code looks fixable. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--include/linux/ptrace.h4
-rw-r--r--include/linux/sched.h2
2 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 0d36750fc0f1..ee918bc6e18c 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -51,6 +51,10 @@
51#ifdef __KERNEL__ 51#ifdef __KERNEL__
52/* 52/*
53 * Ptrace flags 53 * Ptrace flags
54 *
55 * The owner ship rules for task->ptrace which holds the ptrace
56 * flags is simple. When a task is running it owns it's task->ptrace
57 * flags. When the a task is stopped the ptracer owns task->ptrace.
54 */ 58 */
55 59
56#define PT_PTRACED 0x00000001 60#define PT_PTRACED 0x00000001
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 267f15257040..a9d23c7d1b25 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1225,7 +1225,7 @@ static inline int thread_group_empty(task_t *p)
1225 (thread_group_leader(p) && !thread_group_empty(p)) 1225 (thread_group_leader(p) && !thread_group_empty(p))
1226 1226
1227/* 1227/*
1228 * Protects ->fs, ->files, ->mm, ->ptrace, ->group_info, ->comm, keyring 1228 * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
1229 * subscriptions and synchronises with wait4(). Also used in procfs. Also 1229 * subscriptions and synchronises with wait4(). Also used in procfs. Also
1230 * pins the final release of task.io_context. Also protects ->cpuset. 1230 * pins the final release of task.io_context. Also protects ->cpuset.
1231 * 1231 *