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SubjectRe: [PATCH 2/3] rcu: Equip sleepable RCU with lockdep dependency graph checks
On Thu, Jan 12, 2023 at 10:59:54PM -0800, Boqun Feng wrote:
> Although all flavors of RCU are annotated correctly with lockdep as
> recursive read locks, their 'check' parameter of lock_acquire() is
> unset. It means that RCU read locks are not added into the lockdep
> dependency graph therefore deadlock detection based on dependency graph
> won't catch deadlock caused by RCU. This is fine for "non-sleepable" RCU
> flavors since wait-context detection and other context based detection
> can catch these deadlocks. However for sleepable RCU, this is limited.
>
> Actually we can detect the deadlocks caused by SRCU by 1) making
> srcu_read_lock() a 'check'ed recursive read lock and 2) making
> synchronize_srcu() a empty write lock critical section. Even better,
> with the newly introduced lock_sync(), we can avoid false positives
> about irq-unsafe/safe. So do it.
>
> Note that NMI safe SRCU read side critical sections are currently not
> annonated, since step-by-step approach can help us deal with
> false-positives. These may be annotated in the future.
>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

Nice, thank you!!!

Acked-by: Paul E. McKenney <paulmck@kernel.org>

Or if you would prefer that I take the series through -rcu, please just
let me know.

Thanx, Paul

> ---
> include/linux/srcu.h | 23 +++++++++++++++++++++--
> kernel/rcu/srcutiny.c | 2 ++
> kernel/rcu/srcutree.c | 2 ++
> 3 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index 9b9d0bbf1d3c..a1595f8c5155 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -102,6 +102,21 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
> return lock_is_held(&ssp->dep_map);
> }
>
> +static inline void srcu_lock_acquire(struct lockdep_map *map)
> +{
> + lock_map_acquire_read(map);
> +}
> +
> +static inline void srcu_lock_release(struct lockdep_map *map)
> +{
> + lock_map_release(map);
> +}
> +
> +static inline void srcu_lock_sync(struct lockdep_map *map)
> +{
> + lock_map_sync(map);
> +}
> +
> #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
> @@ -109,6 +124,10 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
> return 1;
> }
>
> +#define srcu_lock_acquire(m) do { } while (0)
> +#define srcu_lock_release(m) do { } while (0)
> +#define srcu_lock_sync(m) do { } while (0)
> +
> #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> #define SRCU_NMI_UNKNOWN 0x0
> @@ -182,7 +201,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
>
> srcu_check_nmi_safety(ssp, false);
> retval = __srcu_read_lock(ssp);
> - rcu_lock_acquire(&(ssp)->dep_map);
> + srcu_lock_acquire(&(ssp)->dep_map);
> return retval;
> }
>
> @@ -226,7 +245,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
> {
> WARN_ON_ONCE(idx & ~0x1);
> srcu_check_nmi_safety(ssp, false);
> - rcu_lock_release(&(ssp)->dep_map);
> + srcu_lock_release(&(ssp)->dep_map);
> __srcu_read_unlock(ssp, idx);
> }
>
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index b12fb0cec44d..336af24e0fe3 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -197,6 +197,8 @@ void synchronize_srcu(struct srcu_struct *ssp)
> {
> struct rcu_synchronize rs;
>
> + srcu_lock_sync(&ssp->dep_map);
> +
> RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
> lock_is_held(&rcu_bh_lock_map) ||
> lock_is_held(&rcu_lock_map) ||
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index ca4b5dcec675..408088c73e0e 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -1267,6 +1267,8 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
> {
> struct rcu_synchronize rcu;
>
> + srcu_lock_sync(&ssp->dep_map);
> +
> RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
> lock_is_held(&rcu_bh_lock_map) ||
> lock_is_held(&rcu_lock_map) ||
> --
> 2.38.1
>

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