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Message-Id: <20200402055640.6677-2-frextrite@gmail.com>
Date: Thu, 2 Apr 2020 11:26:39 +0530
From: Amol Grover <frextrite@...il.com>
To: Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
James Morris <jamorris@...ux.microsoft.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Jann Horn <jannh@...gle.com>,
David Howells <dhowells@...hat.com>,
Shakeel Butt <shakeelb@...gle.com>,
"Eric W . Biederman" <ebiederm@...ssion.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Paul Moore <paul@...l-moore.com>,
Eric Paris <eparis@...hat.com>
Cc: linux-kernel-mentees@...ts.linuxfoundation.org,
linux-kernel@...r.kernel.org, linux-audit@...hat.com,
Joel Fernandes <joel@...lfernandes.org>,
Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>,
Amol Grover <frextrite@...il.com>
Subject: [PATCH 2/3 RESEND] cred: Do not use RCU primitives to access cred pointer
Since task_struct::cred can only be used task-synchronously,
and is not visible to other threads under RCU context,
we do not require RCU primitives to read/write to it and incur
heavy barriers.
Suggested-by: Jann Horn <jannh@...gle.com>
Co-developed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Amol Grover <frextrite@...il.com>
---
include/linux/cred.h | 5 ++---
kernel/cred.c | 6 +++---
2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 18639c069263..5973791e5fe4 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -291,11 +291,10 @@ static inline void put_cred(const struct cred *_cred)
/**
* current_cred - Access the current task's subjective credentials
*
- * Access the subjective credentials of the current task. RCU-safe,
- * since nobody else can modify it.
+ * Access the subjective credentials of the current task.
*/
#define current_cred() \
- rcu_dereference_protected(current->cred, 1)
+ (current->cred)
/**
* current_real_cred - Access the current task's objective credentials
diff --git a/kernel/cred.c b/kernel/cred.c
index 809a985b1793..3956c31d068d 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -485,7 +485,7 @@ int commit_creds(struct cred *new)
if (new->user != old->user)
atomic_inc(&new->user->processes);
rcu_assign_pointer(task->real_cred, new);
- rcu_assign_pointer(task->cred, new);
+ task->cred = new;
if (new->user != old->user)
atomic_dec(&old->user->processes);
alter_cred_subscribers(old, -2);
@@ -562,7 +562,7 @@ const struct cred *override_creds(const struct cred *new)
*/
get_new_cred((struct cred *)new);
alter_cred_subscribers(new, 1);
- rcu_assign_pointer(current->cred, new);
+ current->cred = new;
alter_cred_subscribers(old, -1);
kdebug("override_creds() = %p{%d,%d}", old,
@@ -590,7 +590,7 @@ void revert_creds(const struct cred *old)
validate_creds(old);
validate_creds(override);
alter_cred_subscribers(old, 1);
- rcu_assign_pointer(current->cred, old);
+ current->cred = old;
alter_cred_subscribers(override, -1);
put_cred(override);
}
--
2.24.1
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