[PATCH 2/3] 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(a)google.com&gt; Co-developed-by: Joel Fernandes (Google) <joel(a)joelfernandes.org&gt; Signed-off-by: Joel Fernandes (Google) <joel(a)joelfernandes.org&gt; Signed-off-by: Amol Grover <frextrite(a)gmail.com&gt; --- 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