Commit 3d491679 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'locking_urgent_for_v5.9_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull locking fixes from Borislav Petkov:
 "Two fixes from the locking/urgent pile:

   - Fix lockdep's detection of "USED" <- "IN-NMI" inversions (Peter
     Zijlstra)

   - Make percpu-rwsem operations on the semaphore's ->read_count
     IRQ-safe because it can be used in an IRQ context (Hou Tao)"

* tag 'locking_urgent_for_v5.9_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/percpu-rwsem: Use this_cpu_{inc,dec}() for read_count
  locking/lockdep: Fix "USED" <- "IN-NMI" inversions
parents 5674d81c e6b1a44e

include/linux/percpu-rwsem.h

+4 −4
Original line number Diff line number Diff line
@@ -60,7 +60,7 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem) 
	 * anything we did within this RCU-sched read-size critical section.

	 */

	if (likely(rcu_sync_is_idle(&sem->rss)))

		__this_cpu_inc(*sem->read_count);

		this_cpu_inc(*sem->read_count);

	else

		__percpu_down_read(sem, false); /* Unconditional memory barrier */

	/*
@@ -79,7 +79,7 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem) 
	 * Same as in percpu_down_read().

	 */

	if (likely(rcu_sync_is_idle(&sem->rss)))

		__this_cpu_inc(*sem->read_count);

		this_cpu_inc(*sem->read_count);

	else

		ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */

	preempt_enable();
@@ -103,7 +103,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem) 
	 * Same as in percpu_down_read().

	 */

	if (likely(rcu_sync_is_idle(&sem->rss))) {

		__this_cpu_dec(*sem->read_count);

		this_cpu_dec(*sem->read_count);

	} else {

		/*

		 * slowpath; reader will only ever wake a single blocked
@@ -115,7 +115,7 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem) 
		 * aggregate zero, as that is the only time it matters) they

		 * will also see our critical section.

		 */

		__this_cpu_dec(*sem->read_count);

		this_cpu_dec(*sem->read_count);

		rcuwait_wake_up(&sem->writer);

	}

	preempt_enable();

kernel/locking/lockdep.c

+29 −6
Original line number Diff line number Diff line
@@ -3969,13 +3969,18 @@ static int separate_irq_context(struct task_struct *curr, 
static int mark_lock(struct task_struct *curr, struct held_lock *this,

			     enum lock_usage_bit new_bit)

{

	unsigned int new_mask = 1 << new_bit, ret = 1;

	unsigned int old_mask, new_mask, ret = 1;



	if (new_bit >= LOCK_USAGE_STATES) {

		DEBUG_LOCKS_WARN_ON(1);

		return 0;

	}



	if (new_bit == LOCK_USED && this->read)

		new_bit = LOCK_USED_READ;



	new_mask = 1 << new_bit;



	/*

	 * If already set then do not dirty the cacheline,

	 * nor do any checks:
@@ -3988,13 +3993,22 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this, 
	/*

	 * Make sure we didn't race:

	 */

	if (unlikely(hlock_class(this)->usage_mask & new_mask)) {

		graph_unlock();

		return 1;

	}

	if (unlikely(hlock_class(this)->usage_mask & new_mask))

		goto unlock;



	old_mask = hlock_class(this)->usage_mask;

	hlock_class(this)->usage_mask |= new_mask;



	/*

	 * Save one usage_traces[] entry and map both LOCK_USED and

	 * LOCK_USED_READ onto the same entry.

	 */

	if (new_bit == LOCK_USED || new_bit == LOCK_USED_READ) {

		if (old_mask & (LOCKF_USED | LOCKF_USED_READ))

			goto unlock;

		new_bit = LOCK_USED;

	}



	if (!(hlock_class(this)->usage_traces[new_bit] = save_trace()))

		return 0;
@@ -4008,6 +4022,7 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this, 
			return 0;

	}



unlock:

	graph_unlock();



	/*
@@ -4942,12 +4957,20 @@ static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock 
{

#ifdef CONFIG_PROVE_LOCKING

	struct lock_class *class = look_up_lock_class(lock, subclass);

	unsigned long mask = LOCKF_USED;



	/* if it doesn't have a class (yet), it certainly hasn't been used yet */

	if (!class)

		return;



	if (!(class->usage_mask & LOCK_USED))

	/*

	 * READ locks only conflict with USED, such that if we only ever use

	 * READ locks, there is no deadlock possible -- RCU.

	 */

	if (!hlock->read)

		mask |= LOCKF_USED_READ;



	if (!(class->usage_mask & mask))

		return;



	hlock->class_idx = class - lock_classes;

kernel/locking/lockdep_internals.h

+2 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ enum lock_usage_bit { 
#include "lockdep_states.h"

#undef LOCKDEP_STATE

	LOCK_USED,

	LOCK_USED_READ,

	LOCK_USAGE_STATES

};
@@ -40,6 +41,7 @@ enum { 
#include "lockdep_states.h"

#undef LOCKDEP_STATE

	__LOCKF(USED)

	__LOCKF(USED_READ)

};



#define LOCKDEP_STATE(__STATE)	LOCKF_ENABLED_##__STATE |

kernel/locking/percpu-rwsem.c

+2 −2
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ EXPORT_SYMBOL_GPL(percpu_free_rwsem); 


static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem)

{

	__this_cpu_inc(*sem->read_count);

	this_cpu_inc(*sem->read_count);



	/*

	 * Due to having preemption disabled the decrement happens on
@@ -71,7 +71,7 @@ static bool __percpu_down_read_trylock(struct percpu_rw_semaphore *sem) 
	if (likely(!atomic_read_acquire(&sem->block)))

		return true;



	__this_cpu_dec(*sem->read_count);

	this_cpu_dec(*sem->read_count);



	/* Prod writer to re-evaluate readers_active_check() */

	rcuwait_wake_up(&sem->writer);

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