From 175b45ed343a9c547b5f45293d3ea08d38a7b6f4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 14 Mar 2026 04:12:58 -0700 Subject: srcu: Use raw spinlocks so call_srcu() can be used under preempt_disable() Tree SRCU has used non-raw spinlocks for many years, motivated by a desire to avoid unnecessary real-time latency and the absence of any reason to use raw spinlocks. However, the recent use of SRCU in tracing as the underlying implementation of RCU Tasks Trace means that call_srcu() is invoked from preemption-disabled regions of code, which in turn requires that any locks acquired by call_srcu() or its callees must be raw spinlocks. This commit therefore converts SRCU's spinlocks to raw spinlocks. [boqun: Add Fixes tag] Reported-by: Kumar Kartikeya Dwivedi Fixes: c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast") Signed-off-by: Paul E. McKenney Signed-off-by: Boqun Feng Cc: Sebastian Andrzej Siewior --- include/linux/srcutree.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 958cb7ef41cb..dfb31d11ff05 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -34,7 +34,7 @@ struct srcu_data { /* Values: SRCU_READ_FLAVOR_.* */ /* Update-side state. */ - spinlock_t __private lock ____cacheline_internodealigned_in_smp; + raw_spinlock_t __private lock ____cacheline_internodealigned_in_smp; struct rcu_segcblist srcu_cblist; /* List of callbacks.*/ unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */ unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ @@ -55,7 +55,7 @@ struct srcu_data { * Node in SRCU combining tree, similar in function to rcu_data. */ struct srcu_node { - spinlock_t __private lock; + raw_spinlock_t __private lock; unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */ /* if greater than ->srcu_gp_seq. */ unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */ @@ -74,7 +74,7 @@ struct srcu_usage { /* First node at each level. */ int srcu_size_state; /* Small-to-big transition state. */ struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ - spinlock_t __private lock; /* Protect counters and size state. */ + raw_spinlock_t __private lock; /* Protect counters and size state. */ struct mutex srcu_gp_mutex; /* Serialize GP work. */ unsigned long srcu_gp_seq; /* Grace-period seq #. */ unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ @@ -156,7 +156,7 @@ struct srcu_struct { #define __SRCU_USAGE_INIT(name) \ { \ - .lock = __SPIN_LOCK_UNLOCKED(name.lock), \ + .lock = __RAW_SPIN_LOCK_UNLOCKED(name.lock), \ .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \ .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \ .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \ -- cgit v1.2.3 From 7c405fb3279b39244b260b54f1bd6488689ae235 Mon Sep 17 00:00:00 2001 From: Boqun Feng Date: Wed, 18 Mar 2026 17:56:21 -0700 Subject: rcu: Use an intermediate irq_work to start process_srcu() Since commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast") we switched to SRCU in BPF. However as BPF instrument can happen basically everywhere (including where a scheduler lock is held), call_srcu() now needs to avoid acquiring scheduler lock because otherwise it could cause deadlock [1]. Fix this by following what the previous RCU Tasks Trace did: using an irq_work to delay the queuing of the work to start process_srcu(). [boqun: Apply Joel's feedback] [boqun: Apply Andrea's test feedback] Reported-by: Andrea Righi Closes: https://lore.kernel.org/all/abjzvz_tL_siV17s@gpd4/ Fixes: commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast") Link: https://lore.kernel.org/rcu/3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com/ [1] Suggested-by: Zqiang Tested-by: Andrea Righi Tested-by: Paul E. McKenney Tested-by: Joel Fernandes Signed-off-by: Boqun Feng --- include/linux/srcutree.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index dfb31d11ff05..be76fa4fc170 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -95,6 +95,7 @@ struct srcu_usage { unsigned long reschedule_jiffies; unsigned long reschedule_count; struct delayed_work work; + struct irq_work irq_work; struct srcu_struct *srcu_ssp; }; -- cgit v1.2.3 From a6fc88b22bc8d12ad52e8412c667ec0f5bf055af Mon Sep 17 00:00:00 2001 From: Joel Fernandes Date: Mon, 23 Mar 2026 20:14:18 -0400 Subject: srcu: Use irq_work to start GP in tiny SRCU Tiny SRCU's srcu_gp_start_if_needed() directly calls schedule_work(), which acquires the workqueue pool->lock. This causes a lockdep splat when call_srcu() is called with a scheduler lock held, due to: call_srcu() [holding pi_lock] srcu_gp_start_if_needed() schedule_work() -> pool->lock workqueue_init() / create_worker() [holding pool->lock] wake_up_process() -> try_to_wake_up() -> pi_lock Also add irq_work_sync() to cleanup_srcu_struct() to prevent a use-after-free if a queued irq_work fires after cleanup begins. Tested with rcutorture SRCU-T and no lockdep warnings. [ Thanks to Boqun for similar fix in patch "rcu: Use an intermediate irq_work to start process_srcu()" ] Signed-off-by: Joel Fernandes Reviewed-by: Paul E. McKenney Signed-off-by: Boqun Feng --- include/linux/srcutiny.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux') diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h index dec7cbe015aa..905b629e8fa3 100644 --- a/include/linux/srcutiny.h +++ b/include/linux/srcutiny.h @@ -11,6 +11,7 @@ #ifndef _LINUX_SRCU_TINY_H #define _LINUX_SRCU_TINY_H +#include #include struct srcu_struct { @@ -24,18 +25,21 @@ struct srcu_struct { struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */ struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */ struct work_struct srcu_work; /* For driving grace periods. */ + struct irq_work srcu_irq_work; /* Defer schedule_work() to irq work. */ #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ }; void srcu_drive_gp(struct work_struct *wp); +void srcu_tiny_irq_work(struct irq_work *irq_work); #define __SRCU_STRUCT_INIT(name, __ignored, ___ignored, ____ignored) \ { \ .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \ .srcu_cb_tail = &name.srcu_cb_head, \ .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \ + .srcu_irq_work = { .func = srcu_tiny_irq_work }, \ __SRCU_DEP_MAP_INIT(name) \ } -- cgit v1.2.3