[tip:core/urgent] task_work: Revert "hold task_lock around checks in keyctl"

From: tip-bot for Oleg Nesterov
Date: Fri Sep 14 2012 - 02:10:35 EST

Commit-ID: b3f68f16dbcde6fcdf0fd27695391ff7e9d41233
Gitweb: http://git.kernel.org/tip/b3f68f16dbcde6fcdf0fd27695391ff7e9d41233
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Sun, 26 Aug 2012 21:12:14 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 13 Sep 2012 16:47:36 +0200

task_work: Revert "hold task_lock around checks in keyctl"

This reverts commit d35abdb28824cf74f0a106a0f9c6f3ff700a35bf.

task_lock() was added to ensure exit_mm() and thus exit_task_work() is
not possible before task_work_add().

This is wrong, task_lock() must not be nested with write_lock(tasklist).
And this is no longer needed, task_work_add() now fails if it is called
after exit_task_work().

Reported-by: Dave Jones <davej@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20120826191214.GA4231@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
security/keys/keyctl.c | 2 --
1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 3364fbf..6cfc647 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1486,7 +1486,6 @@ long keyctl_session_to_parent(void)
oldwork = NULL;
parent = me->real_parent;

- task_lock(parent);
/* the parent mustn't be init and mustn't be a kernel thread */
if (parent->pid <= 1 || !parent->mm)
goto unlock;
@@ -1530,7 +1529,6 @@ long keyctl_session_to_parent(void)
if (!ret)
newwork = NULL;
- task_unlock(parent);
if (oldwork)
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