Commit aba9da09 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'rcu-fixes.v7.0-20260325a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux 

Pull RCU fixes from Boqun Feng:
 "Fix a regression introduced by commit c27cea44 ("rcu: Re-implement
  RCU Tasks Trace in terms of SRCU-fast"): BPF contexts can run with
  preemption disabled or scheduler locks held, so call_srcu() must work
  in all such contexts.

  Fix this by converting SRCU's spinlocks to raw spinlocks and avoiding
  scheduler lock acquisition in call_srcu() by deferring to an irq_work
  (similar to call_rcu_tasks_generic()), for both tree SRCU and tiny
  SRCU.

  Also fix a follow-on lockdep splat caused by srcu_node allocation
  under the newly introduced raw spinlock by deferring the allocation to
  grace-period worker context"

* tag 'rcu-fixes.v7.0-20260325a' of git://git.kernel.org/pub/scm/linux/kernel/git/rcu/linux:
  srcu: Use irq_work to start GP in tiny SRCU
  rcu: Use an intermediate irq_work to start process_srcu()
  srcu: Push srcu_node allocation to GP when non-preemptible
  srcu: Use raw spinlocks so call_srcu() can be used under preempt_disable()
parents d2a43e7f a6fc88b2

include/linux/srcutiny.h

+4 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#ifndef _LINUX_SRCU_TINY_H

#define _LINUX_SRCU_TINY_H



#include <linux/irq_work_types.h>

#include <linux/swait.h>



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)					\

}

include/linux/srcutree.h

+5 −4
Original line number Diff line number Diff line
@@ -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. */
@@ -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;

};
@@ -156,7 +157,7 @@ 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,					\

kernel/rcu/rcu.h

+9 −0
Original line number Diff line number Diff line
@@ -502,6 +502,15 @@ do { \ 
	___locked;							\

})



#define raw_spin_trylock_irqsave_rcu_node(p, flags)			\

({									\

	bool ___locked = raw_spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \

									\

	if (___locked)							\

		smp_mb__after_unlock_lock();				\

	___locked;							\

})



#define raw_lockdep_assert_held_rcu_node(p)				\

	lockdep_assert_held(&ACCESS_PRIVATE(p, lock))

kernel/rcu/srcutiny.c

+18 −1
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
 */



#include <linux/export.h>

#include <linux/irq_work.h>

#include <linux/mutex.h>

#include <linux/preempt.h>

#include <linux/rcupdate_wait.h>
@@ -41,6 +42,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) 
	ssp->srcu_idx_max = 0;

	INIT_WORK(&ssp->srcu_work, srcu_drive_gp);

	INIT_LIST_HEAD(&ssp->srcu_work.entry);

	init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work);

	return 0;

}
@@ -84,6 +86,7 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); 
void cleanup_srcu_struct(struct srcu_struct *ssp)

{

	WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);

	irq_work_sync(&ssp->srcu_irq_work);

	flush_work(&ssp->srcu_work);

	WARN_ON(ssp->srcu_gp_running);

	WARN_ON(ssp->srcu_gp_waiting);
@@ -177,6 +180,20 @@ void srcu_drive_gp(struct work_struct *wp) 
}

EXPORT_SYMBOL_GPL(srcu_drive_gp);



/*

 * Use an irq_work to defer schedule_work() to avoid acquiring the workqueue

 * pool->lock while the caller might hold scheduler locks, causing lockdep

 * splats due to workqueue_init() doing a wakeup.

 */

void srcu_tiny_irq_work(struct irq_work *irq_work)

{

	struct srcu_struct *ssp;



	ssp = container_of(irq_work, struct srcu_struct, srcu_irq_work);

	schedule_work(&ssp->srcu_work);

}

EXPORT_SYMBOL_GPL(srcu_tiny_irq_work);



static void srcu_gp_start_if_needed(struct srcu_struct *ssp)

{

	unsigned long cookie;
@@ -189,7 +206,7 @@ static void srcu_gp_start_if_needed(struct srcu_struct *ssp) 
	WRITE_ONCE(ssp->srcu_idx_max, cookie);

	if (!READ_ONCE(ssp->srcu_gp_running)) {

		if (likely(srcu_init_done))

			schedule_work(&ssp->srcu_work);

			irq_work_queue(&ssp->srcu_irq_work);

		else if (list_empty(&ssp->srcu_work.entry))

			list_add(&ssp->srcu_work.entry, &srcu_boot_list);

	}

kernel/rcu/srcutree.c

+102 −109

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