6.6-stable review patch. If anyone has any objections, please let me know.
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From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ Upstream commit 3c6b0c1c28184038d90dffe8eb542bedcb8ccf98 ]
It is claimed that srcu_read_lock_nmisafe() NMI-safe. However it triggers a lockdep if used from NMI because lockdep expects a deadlock since nothing disables NMIs while the lock is acquired.
This is because commit f0f44752f5f61 ("rcu: Annotate SRCU's update-side lockdep dependencies") annotates synchronize_srcu() as a write lock usage. This helps to detect a deadlocks such as srcu_read_lock(); synchronize_srcu(); srcu_read_unlock();
The side effect is that the lock srcu_struct now has a USED usage in normal contexts, so it conflicts with a USED_READ usage in NMI. But this shouldn't cause a real deadlock because the write lock usage from synchronize_srcu() is a fake one and only used for read/write deadlock detection.
Use a try-lock annotation for srcu_read_lock_nmisafe() to avoid lockdep complains if used from NMI.
Fixes: f0f44752f5f6 ("rcu: Annotate SRCU's update-side lockdep dependencies") Link: https://lore.kernel.org/r/20230927160231.XRCDDSK4@linutronix.de Reviewed-by: Boqun Feng boqun.feng@gmail.com Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Neeraj Upadhyay (AMD) neeraj.iitr10@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/rcupdate.h | 6 ++++++ include/linux/srcu.h | 2 +- 2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5e5f920ade90..44aab5c0bd2c 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -303,6 +303,11 @@ static inline void rcu_lock_acquire(struct lockdep_map *map) lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_); }
+static inline void rcu_try_lock_acquire(struct lockdep_map *map) +{ + lock_acquire(map, 0, 1, 2, 0, NULL, _THIS_IP_); +} + static inline void rcu_lock_release(struct lockdep_map *map) { lock_release(map, _THIS_IP_); @@ -317,6 +322,7 @@ int rcu_read_lock_any_held(void); #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
# define rcu_lock_acquire(a) do { } while (0) +# define rcu_try_lock_acquire(a) do { } while (0) # define rcu_lock_release(a) do { } while (0)
static inline int rcu_read_lock_held(void) diff --git a/include/linux/srcu.h b/include/linux/srcu.h index 127ef3b2e607..236610e4a8fa 100644 --- a/include/linux/srcu.h +++ b/include/linux/srcu.h @@ -229,7 +229,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
srcu_check_nmi_safety(ssp, true); retval = __srcu_read_lock_nmisafe(ssp); - rcu_lock_acquire(&ssp->dep_map); + rcu_try_lock_acquire(&ssp->dep_map); return retval; }