linux-kernel - [PATCH 4/4] proc: task_state: ptrace_parent() doesn't need pid

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Message-ID: <20141107201454.GA22246@redhat.com>
Date:	Fri, 7 Nov 2014 21:14:54 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Aaron Tomlin <atomlin@...hat.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sterling Alexander <stalexan@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] proc: task_state: ptrace_parent() doesn't need
	pid_alive() check

p->ptrace != 0 means that release_task(p) was not called, so pid_alive()
buys nothing and we can remove this check. Other callers already use it
directly without additional checks.

Note: with or without this patch ptrace_parent() can return the pointer
to the freed task, this will be explained/fixed later.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/proc/array.c |   13 ++++++-------
 1 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 800e30f..bd117d0 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -157,19 +157,18 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	struct user_namespace *user_ns = seq_user_ns(m);
 	struct group_info *group_info;
 	int g;
+	struct task_struct *tracer;
 	const struct cred *cred;
-	pid_t ppid, tpid, tgid, ngid;
+	pid_t ppid, tpid = 0, tgid, ngid;
 	unsigned int max_fds = 0;
 
 	rcu_read_lock();
 	ppid = pid_alive(p) ?
 		task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
-	tpid = 0;
-	if (pid_alive(p)) {
-		struct task_struct *tracer = ptrace_parent(p);
-		if (tracer)
-			tpid = task_pid_nr_ns(tracer, ns);
-	}
+
+	tracer = ptrace_parent(p);
+	if (tracer)
+		tpid = task_pid_nr_ns(tracer, ns);
 
 	tgid = task_tgid_nr_ns(p, ns);
 	ngid = task_numa_group_id(p);
-- 
1.5.5.1

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