On Thu, Jan 23, 2020 at 08:23:05PM +0530, madhuparnabhowmik10@xxxxxxxxx wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
>
> This patch fixes the following sparse errors by annotating the
> sighand_struct with __rcu
>
> kernel/fork.c:1511:9: error: incompatible types in comparison expression
> kernel/exit.c:100:19: error: incompatible types in comparison expression
> kernel/signal.c:1370:27: error: incompatible types in comparison expression
>
> This fix introduces the following sparse error in signal.c due to
> checking the sighand pointer without rcu primitives:
>
> kernel/signal.c:1386:21: error: incompatible types in comparison expression
>
> This new sparse error is also addressed in this patch.
>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx>
> ---
> include/linux/sched.h | 2 +-
> kernel/signal.c | 3 ++-
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b511e178a89f..7a351360ad54 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -918,7 +918,7 @@ struct task_struct {
>
> /* Signal handlers: */
> struct signal_struct *signal;
> - struct sighand_struct *sighand;
> + struct sighand_struct __rcu *sighand;
> sigset_t blocked;
> sigset_t real_blocked;
> /* Restored if set_restore_sigmask() was used: */
> diff --git a/kernel/signal.c b/kernel/signal.c
> index bcd46f547db3..1272def37462 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1383,7 +1383,8 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
> * must see ->sighand == NULL.
> */
> spin_lock_irqsave(&sighand->siglock, *flags);
> - if (likely(sighand == tsk->sighand))
> + if (likely(sighand == rcu_dereference_protected(tsk->sighand,
> + lockdep_is_held(&sighand->siglock))))
Given that the return value is never dereferenced, you can use
rcu_access_pointer(), which may be used outside of an RCU read-side
critical section, and thus does not need the lockdep_is_held(). So this
change would save a line of code and would be a bit easier on the eyes.
Thanx, Paul
> break;
> spin_unlock_irqrestore(&sighand->siglock, *flags);
> }
> --
> 2.17.1
>
