linux-kernel - [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist

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Date:   Tue,  6 Jun 2017 14:03:18 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-api@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Roland McGrath <roland@...k.frob.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 06/26] rlimit: Remove unnecessary grab of tasklist_lock

There is no reason to take the tasklist lock here.  The sighand
structure is never referenced and and tsk->signal is guaranteed
to stick around until tsk is freed. Further update_rlimit_cpu
does not need the tasklist_lock.  And the rlim_lock is used
to guarantee mutual exclusion.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/sys.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 8a94b4eabcaa..705f14b28134 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1380,13 +1380,6 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource,
 			return -EPERM;
 	}
 
-	/* protect tsk->signal and tsk->sighand from disappearing */
-	read_lock(&tasklist_lock);
-	if (!tsk->sighand) {
-		retval = -ESRCH;
-		goto out;
-	}
-
 	rlim = tsk->signal->rlim + resource;
 	task_lock(tsk->group_leader);
 	if (new_rlim) {
@@ -1425,8 +1418,7 @@ int do_prlimit(struct task_struct *tsk, unsigned int resource,
 	     new_rlim->rlim_cur != RLIM_INFINITY &&
 	     IS_ENABLED(CONFIG_POSIX_TIMERS))
 		update_rlimit_cpu(tsk, new_rlim->rlim_cur);
-out:
-	read_unlock(&tasklist_lock);
+
 	return retval;
 }
 
-- 
2.10.1