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authorTejun Heo <tj@kernel.org>2011-12-12 18:12:21 -0800
committerTejun Heo <tj@kernel.org>2011-12-12 18:12:21 -0800
commit77e4ef99d1c596a31747668e5fd837f77b6349b6 (patch)
treeb9dcc8d73f9febf6a18edc0b2efa3ecddc2a7a35 /kernel/signal.c
parent257058ae2b971646b96ab3a15605ac69186e562a (diff)
threadgroup: extend threadgroup_lock() to cover exit and exec
threadgroup_lock() protected only protected against new addition to the threadgroup, which was inherently somewhat incomplete and problematic for its only user cgroup. On-going migration could race against exec and exit leading to interesting problems - the symmetry between various attach methods, task exiting during method execution, ->exit() racing against attach methods, migrating task switching basic properties during exec and so on. This patch extends threadgroup_lock() such that it protects against all three threadgroup altering operations - fork, exit and exec. For exit, threadgroup_change_begin/end() calls are added to exit_signals around assertion of PF_EXITING. For exec, threadgroup_[un]lock() are updated to also grab and release cred_guard_mutex. With this change, threadgroup_lock() guarantees that the target threadgroup will remain stable - no new task will be added, no new PF_EXITING will be set and exec won't happen. The next patch will update cgroup so that it can take full advantage of this change. -v2: beefed up comment as suggested by Frederic. -v3: narrowed scope of protection in exit path as suggested by Frederic. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Li Zefan <lizf@cn.fujitsu.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Paul Menage <paul@paulmenage.org> Cc: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/signal.c')
-rw-r--r--kernel/signal.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/signal.c b/kernel/signal.c
index b3f78d09a10..399c184bf0a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2359,8 +2359,15 @@ void exit_signals(struct task_struct *tsk)
int group_stop = 0;
sigset_t unblocked;
+ /*
+ * @tsk is about to have PF_EXITING set - lock out users which
+ * expect stable threadgroup.
+ */
+ threadgroup_change_begin(tsk);
+
if (thread_group_empty(tsk) || signal_group_exit(tsk->signal)) {
tsk->flags |= PF_EXITING;
+ threadgroup_change_end(tsk);
return;
}
@@ -2370,6 +2377,9 @@ void exit_signals(struct task_struct *tsk)
* see wants_signal(), do_signal_stop().
*/
tsk->flags |= PF_EXITING;
+
+ threadgroup_change_end(tsk);
+
if (!signal_pending(tsk))
goto out;