linux-kernel - [PATCH v2 1/2] proc: Use PIDTYPE_TGID in next

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Message-ID: <87368uxa8x.fsf_-_@x220.int.ebiederm.org>
Date:   Thu, 23 Apr 2020 14:39:10 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Alexey Gladkov <legion@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v2 1/2] proc: Use PIDTYPE_TGID in next_tgid


Combine the pid_task and thes test has_group_leader_pid into a single
dereference by using pid_task(PIDTYPE_TGID).

This makes the code simpler and proof against needing to even think
about any shenanigans that de_thread might get up to.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/proc/base.c | 16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 2868bff1a142..a48b4d4056a9 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3360,20 +3360,8 @@ static struct tgid_iter next_tgid(struct pid_namespace *ns, struct tgid_iter ite
 	pid = find_ge_pid(iter.tgid, ns);
 	if (pid) {
 		iter.tgid = pid_nr_ns(pid, ns);
-		iter.task = pid_task(pid, PIDTYPE_PID);
-		/* What we to know is if the pid we have find is the
-		 * pid of a thread_group_leader.  Testing for task
-		 * being a thread_group_leader is the obvious thing
-		 * todo but there is a window when it fails, due to
-		 * the pid transfer logic in de_thread.
-		 *
-		 * So we perform the straight forward test of seeing
-		 * if the pid we have found is the pid of a thread
-		 * group leader, and don't worry if the task we have
-		 * found doesn't happen to be a thread group leader.
-		 * As we don't care in the case of readdir.
-		 */
-		if (!iter.task || !has_group_leader_pid(iter.task)) {
+		iter.task = pid_task(pid, PIDTYPE_TGID);
+		if (!iter.task) {
 			iter.tgid += 1;
 			goto retry;
 		}
-- 
2.20.1