rcu: Move preemption disabling out of __srcu_read_lock()

Currently, __srcu_read_lock() cannot be invoked from restricted
environments because it contains calls to preempt_disable() and
preempt_enable(), both of which can invoke lockdep, which is a bad
idea in some restricted execution modes.  This commit therefore moves
the preempt_disable() and preempt_enable() from __srcu_read_lock()
to srcu_read_lock().  It also inserts the preempt_disable() and
preempt_enable() around the call to __srcu_read_lock() in do_exit().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index bdeb4567b71e55edc785d5173f5ccc15ec0cda69..f5f80c5643ac5669abbb1e3e736ded2f49b5f3a0 100644 (file)
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  */
 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 {
-       int retval = __srcu_read_lock(sp);
+       int retval;
 
+       preempt_disable();
+       retval = __srcu_read_lock(sp);
+       preempt_enable();
        rcu_lock_acquire(&(sp)->dep_map);
        return retval;
 }

diff --git a/kernel/exit.c b/kernel/exit.c
index ea95ee1b5ef7038ec1ade3f5cd5d98181177f22f..0e93b63bbc59292815f49ddc95c0eceafa48b7e4 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -761,7 +761,9 @@ void do_exit(long code)
         */
        flush_ptrace_hw_breakpoint(tsk);
 
+       TASKS_RCU(preempt_disable());
        TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
+       TASKS_RCU(preempt_enable());
        exit_notify(tsk, group_dead);
        proc_exit_connector(tsk);
 #ifdef CONFIG_NUMA

diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 9e6122540d28429a2f1902c13b5e92ade124a624..a63a1ea5a41bf450f6b162674149a5928fca3530 100644 (file)
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -298,11 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp)
        int idx;
 
        idx = READ_ONCE(sp->completed) & 0x1;
-       preempt_disable();
        __this_cpu_inc(sp->per_cpu_ref->c[idx]);
        smp_mb(); /* B */  /* Avoid leaking the critical section. */
        __this_cpu_inc(sp->per_cpu_ref->seq[idx]);
-       preempt_enable();
        return idx;
 }
 EXPORT_SYMBOL_GPL(__srcu_read_lock);