Commit 7cdacc5f authored by Yanfei Xu's avatar Yanfei Xu Committed by Peter Zijlstra
Browse files

locking/rwsem: Disable preemption for spinning region 



The spinning region rwsem_spin_on_owner() should not be preempted,
however the rwsem_down_write_slowpath() invokes it and don't disable
preemption. Fix it by adding a pair of preempt_disable/enable().

Signed-off-by: default avatarYanfei Xu <yanfei.xu@windriver.com>
[peterz: Fix CONFIG_RWSEM_SPIN_ON_OWNER=n build]
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWaiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20211013134154.1085649-3-yanfei.xu@windriver.com
parent bc67f1c4

kernel/locking/rwsem.c

+30 −23
Original line number Diff line number Diff line
@@ -577,6 +577,24 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem, 
	return true;

}



/*

 * The rwsem_spin_on_owner() function returns the following 4 values

 * depending on the lock owner state.

 *   OWNER_NULL  : owner is currently NULL

 *   OWNER_WRITER: when owner changes and is a writer

 *   OWNER_READER: when owner changes and the new owner may be a reader.

 *   OWNER_NONSPINNABLE:

 *		   when optimistic spinning has to stop because either the

 *		   owner stops running, is unknown, or its timeslice has

 *		   been used up.

 */

enum owner_state {

	OWNER_NULL		= 1 << 0,

	OWNER_WRITER		= 1 << 1,

	OWNER_READER		= 1 << 2,

	OWNER_NONSPINNABLE	= 1 << 3,

};



#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

/*

 * Try to acquire write lock before the writer has been put on wait queue.
@@ -632,23 +650,6 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) 
	return ret;

}



/*

 * The rwsem_spin_on_owner() function returns the following 4 values

 * depending on the lock owner state.

 *   OWNER_NULL  : owner is currently NULL

 *   OWNER_WRITER: when owner changes and is a writer

 *   OWNER_READER: when owner changes and the new owner may be a reader.

 *   OWNER_NONSPINNABLE:

 *		   when optimistic spinning has to stop because either the

 *		   owner stops running, is unknown, or its timeslice has

 *		   been used up.

 */

enum owner_state {

	OWNER_NULL		= 1 << 0,

	OWNER_WRITER		= 1 << 1,

	OWNER_READER		= 1 << 2,

	OWNER_NONSPINNABLE	= 1 << 3,

};

#define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER | OWNER_READER)



static inline enum owner_state
@@ -878,12 +879,11 @@ static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem) 


static inline void clear_nonspinnable(struct rw_semaphore *sem) { }



static inline int

static inline enum owner_state

rwsem_spin_on_owner(struct rw_semaphore *sem)

{

	return 0;

	return OWNER_NONSPINNABLE;

}

#define OWNER_NULL	1

#endif



/*
@@ -1095,9 +1095,16 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state) 
		 * In this case, we attempt to acquire the lock again

		 * without sleeping.

		 */

		if (wstate == WRITER_HANDOFF &&

		    rwsem_spin_on_owner(sem) == OWNER_NULL)

		if (wstate == WRITER_HANDOFF) {

			enum owner_state owner_state;



			preempt_disable();

			owner_state = rwsem_spin_on_owner(sem);

			preempt_enable();



			if (owner_state == OWNER_NULL)

				goto trylock_again;

		}



		/* Block until there are no active lockers. */

		for (;;) {