On Tue, Oct 06, 2015 at 09:13:42AM -0700, Paul E. McKenney wrote:
> 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().
What restricted environments do you intend to invoke
__srcu_read_lock from?
This change seems fine, but I don't see any change in this patch series
that needs this, hence my curiosity.
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> include/linux/srcu.h | 5 ++++-
> kernel/exit.c | 2 ++
> kernel/rcu/srcu.c | 2 --
> 3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index bdeb4567b71e..f5f80c5643ac 100644
> --- 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 ea95ee1b5ef7..0e93b63bbc59 100644
> --- 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 9e6122540d28..a63a1ea5a41b 100644
> --- 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);
> --
> 2.5.2
>
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