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authorRoland McGrath <roland@redhat.com>2005-10-30 15:02:50 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2005-10-30 17:37:24 -0800
commit7f2a52555998c699a7e89f24636c909d6fc08a60 (patch)
tree98ef1254ab3e727ba3470d4eeaf064d5dcb48614 /kernel/exit.c
parent396dc44bcac58f464b7b23c345052e37881cccea (diff)
[PATCH] wait4 PTRACE_ATTACH race fix
Back about a year ago when I last fiddled heavily with the do_wait code, I was thinking too hard about the wrong thing and I now think I introduced a bug whose inverse thought I was fixing. Apparently noone was looking too hard over much shoulder, so as to cite my bogus reasoning at the time. In the race condition when PTRACE_ATTACH is about to steal a child and then the child hits a tracing event (what my_ptrace_child checks for), the real parent does need to set its flag noting it has some eligible live children. Otherwise a spurious ECHILD error is possible, since the child in question is not yet on the ptrace_children list. Signed-off-by: Roland McGrath <roland@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/exit.c')
-rw-r--r--kernel/exit.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 6ef8f7356a7..2d39ccc367e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1383,6 +1383,15 @@ repeat:
switch (p->state) {
case TASK_TRACED:
+ /*
+ * When we hit the race with PTRACE_ATTACH,
+ * we will not report this child. But the
+ * race means it has not yet been moved to
+ * our ptrace_children list, so we need to
+ * set the flag here to avoid a spurious ECHILD
+ * when the race happens with the only child.
+ */
+ flag = 1;
if (!my_ptrace_child(p))
continue;
/*FALLTHROUGH*/