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authorRoland McGrath <roland@redhat.com>2006-12-06 20:36:34 -0800
committerLinus Torvalds <torvalds@woody.osdl.org>2006-12-07 08:39:33 -0800
commitfec1d0115240593b39898289e6e1413ea6e44a84 (patch)
tree9e0c5506118a5fb84d1b21195323dd1c3d7588ea
parent736c4b8572ac24b1e6fd58d00872305a120ac700 (diff)
[PATCH] Disable CLONE_CHILD_CLEARTID for abnormal exit
The CLONE_CHILD_CLEARTID flag is used by NPTL to have its threads communicate via memory/futex when they exit, so pthread_join can synchronize using a simple futex wait. The word of user memory where NPTL stores a thread's own TID is what it passes; this gets reset to zero at thread exit. It is not desireable to touch this user memory when threads are dying due to a fatal signal. A core dump is more usefully representative of the dying program state if the threads live at the time of the crash have their NPTL data structures unperturbed. The userland expectation of CLONE_CHILD_CLEARTID has only ever been that it works for a thread making an _exit system call. This problem was identified by Ernie Petrides <petrides@redhat.com>. Signed-off-by: Roland McGrath <roland@redhat.com> Cc: Ernie Petrides <petrides@redhat.com> Cc: Jakub Jelinek <jakub@redhat.com> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Ulrich Drepper <drepper@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/fork.c11
1 files changed, 10 insertions, 1 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 2cf74edd329..f37980df1d5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -448,7 +448,16 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
tsk->vfork_done = NULL;
complete(vfork_done);
}
- if (tsk->clear_child_tid && atomic_read(&mm->mm_users) > 1) {
+
+ /*
+ * If we're exiting normally, clear a user-space tid field if
+ * requested. We leave this alone when dying by signal, to leave
+ * the value intact in a core dump, and to save the unnecessary
+ * trouble otherwise. Userland only wants this done for a sys_exit.
+ */
+ if (tsk->clear_child_tid
+ && !(tsk->flags & PF_SIGNALED)
+ && atomic_read(&mm->mm_users) > 1) {
u32 __user * tidptr = tsk->clear_child_tid;
tsk->clear_child_tid = NULL;