Commit 7f2a5255 authored by Roland McGrath's avatar Roland McGrath Committed by Linus Torvalds
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[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: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 396dc44b
......@@ -1383,6 +1383,15 @@ static long do_wait(pid_t pid, int options, struct siginfo __user *infop,
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*/
......
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