On Wed, Jul 21, 2021 at 01:21:18PM -0700, Paul E. McKenney wrote:
> This commit marks some interrupt-induced read-side data races in
> __srcu_read_lock(), __srcu_read_unlock(), and srcu_torture_stats_print().
>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> include/linux/srcutiny.h | 8 ++++----
> kernel/rcu/srcutiny.c | 2 +-
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
> index 0e0cf4d6a72a0..6cfaa0a9a9b96 100644
> --- a/include/linux/srcutiny.h
> +++ b/include/linux/srcutiny.h
> @@ -61,7 +61,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
> int idx;
>
> idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> - WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
> + WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
> return idx;
> }
>
> @@ -81,11 +81,11 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
> {
> int idx;
>
> - idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> + idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
This looks very weird, any explanation why we want to put data_race() on
a READ_ONCE()?
Regards,
Boqun
> pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
> tt, tf, idx,
> - READ_ONCE(ssp->srcu_lock_nesting[!idx]),
> - READ_ONCE(ssp->srcu_lock_nesting[idx]));
> + data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
> + data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
> }
>
> #endif
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 26344dc6483b0..a0ba2ed49bc61 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -96,7 +96,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
> */
> void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
> {
> - int newval = ssp->srcu_lock_nesting[idx] - 1;
> + int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
>
> WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
> if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
> --
> 2.31.1.189.g2e36527f23
>
