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ptrace: simplify ptrace_exit()->ignoring_children() path 

ignoring_children() takes parent->sighand->siglock and checks
k_sigaction[SIGCHLD] atomically.  But this buys nothing, we can't get the
"really" wrong result even if we race with sigaction(SIGCHLD).  If we read
the "stale" sa_handler/sa_flags we can pretend it was changed right after
the check.

Remove spin_lock(->siglock), and kill "int ign" which caches the result of
ignoring_children() which becomes rather trivial.

Perhaps it makes sense to export this helper, do_notify_parent() can use
it too.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2009-04-02 16:58:12 -07:00 committed by Linus Torvalds
parent 95c3eb76dc
commit 6d69cb87f0
1 changed files with 8 additions and 17 deletions
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25
kernel/exit.c
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@ -732,19 +732,15 @@ static void exit_mm(struct task_struct * tsk)
}
/*
* Return nonzero if @parent's children should reap themselves.
*
* Called with write_lock_irq(&tasklist_lock) held.
* Called with irqs disabled, returns true if childs should reap themselves.
*/
static int ignoring_children(struct task_struct *parent)
static int ignoring_children(struct sighand_struct *sigh)
{
int ret;
struct sighand_struct *psig = parent->sighand;
unsigned long flags;
spin_lock_irqsave(&psig->siglock, flags);
ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||
(psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT));
spin_unlock_irqrestore(&psig->siglock, flags);
spin_lock(&sigh->siglock);
ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
(sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
spin_unlock(&sigh->siglock);
return ret;
}
@ -757,7 +753,6 @@ static int ignoring_children(struct task_struct *parent)
static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
{
struct task_struct *p, *n;
int ign = -1;
list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {
__ptrace_unlink(p);
@ -779,12 +774,8 @@ static void ptrace_exit(struct task_struct *parent, struct list_head *dead)
if (!task_detached(p) && thread_group_empty(p)) {
if (!same_thread_group(p->real_parent, parent))
do_notify_parent(p, p->exit_signal);
else {
if (ign < 0)
ign = ignoring_children(parent);
if (ign)
p->exit_signal = -1;
}
else if (ignoring_children(parent->sighand))
p->exit_signal = -1;
}
if (task_detached(p)) {