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Commit d4799608 authored by Michal Hocko's avatar Michal Hocko Committed by Ingo Molnar
Browse files

locking/rwsem: Introduce basis for down_write_killable() 



Introduce a generic implementation necessary for down_write_killable().

This is a trivial extension of the already existing down_write() call
which can be interrupted by SIGKILL.  This patch doesn't provide
down_write_killable() yet because arches have to provide the necessary
pieces before.

rwsem_down_write_failed() which is a generic slow path for the
write lock is extended to take a task state and renamed to
__rwsem_down_write_failed_common(). The return value is either a valid
semaphore pointer or ERR_PTR(-EINTR).

rwsem_down_write_failed_killable() is exported as a new way to wait for
the lock and be killable.

For rwsem-spinlock implementation the current __down_write() it updated
in a similar way as __rwsem_down_write_failed_common() except it doesn't
need new exports just visible __down_write_killable().

Architectures which are not using the generic rwsem implementation are
supposed to provide their __down_write_killable() implementation and
use rwsem_down_write_failed_killable() for the slow path.

Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-alpha@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: linux-xtensa@linux-xtensa.org
Cc: sparclinux@vger.kernel.org
Link: http://lkml.kernel.org/r/1460041951-22347-7-git-send-email-mhocko@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 938072e3

include/asm-generic/rwsem.h

+12 −0
Original line number Diff line number Diff line
@@ -63,6 +63,18 @@ static inline void __down_write(struct rw_semaphore *sem) 
		rwsem_down_write_failed(sem);

}



static inline int __down_write_killable(struct rw_semaphore *sem)

{

	long tmp;



	tmp = atomic_long_add_return_acquire(RWSEM_ACTIVE_WRITE_BIAS,

				     (atomic_long_t *)&sem->count);

	if (unlikely(tmp != RWSEM_ACTIVE_WRITE_BIAS))

		if (IS_ERR(rwsem_down_write_failed_killable(sem)))

			return -EINTR;

	return 0;

}



static inline int __down_write_trylock(struct rw_semaphore *sem)

{

	long tmp;

include/linux/rwsem-spinlock.h

+1 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ struct rw_semaphore { 
extern void __down_read(struct rw_semaphore *sem);

extern int __down_read_trylock(struct rw_semaphore *sem);

extern void __down_write(struct rw_semaphore *sem);

extern int __must_check __down_write_killable(struct rw_semaphore *sem);

extern int __down_write_trylock(struct rw_semaphore *sem);

extern void __up_read(struct rw_semaphore *sem);

extern void __up_write(struct rw_semaphore *sem);

include/linux/rwsem.h

+2 −0
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
#include <linux/list.h>

#include <linux/spinlock.h>

#include <linux/atomic.h>

#include <linux/err.h>

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER

#include <linux/osq_lock.h>

#endif
@@ -43,6 +44,7 @@ struct rw_semaphore { 


extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);

extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);

extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);

extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);

extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);

kernel/locking/rwsem-spinlock.c

+20 −2
Original line number Diff line number Diff line
@@ -191,11 +191,12 @@ int __down_read_trylock(struct rw_semaphore *sem) 
/*

 * get a write lock on the semaphore

 */

void __sched __down_write(struct rw_semaphore *sem)

int __sched __down_write_common(struct rw_semaphore *sem, int state)

{

	struct rwsem_waiter waiter;

	struct task_struct *tsk;

	unsigned long flags;

	int ret = 0;



	raw_spin_lock_irqsave(&sem->wait_lock, flags);
@@ -215,16 +216,33 @@ void __sched __down_write(struct rw_semaphore *sem) 
		 */

		if (sem->count == 0)

			break;

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		if (signal_pending_state(state, current)) {

			ret = -EINTR;

			goto out;

		}

		set_task_state(tsk, state);

		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);

		schedule();

		raw_spin_lock_irqsave(&sem->wait_lock, flags);

	}

	/* got the lock */

	sem->count = -1;

out:

	list_del(&waiter.list);



	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);



	return ret;

}



void __sched __down_write(struct rw_semaphore *sem)

{

	__down_write_common(sem, TASK_UNINTERRUPTIBLE);

}



int __sched __down_write_killable(struct rw_semaphore *sem)

{

	return __down_write_common(sem, TASK_KILLABLE);

}



/*

kernel/locking/rwsem-xadd.c

+25 −6
Original line number Diff line number Diff line
@@ -433,12 +433,13 @@ static inline bool rwsem_has_spinner(struct rw_semaphore *sem) 
/*

 * Wait until we successfully acquire the write lock

 */

__visible

struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)

static inline struct rw_semaphore *

__rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)

{

	long count;

	bool waiting = true; /* any queued threads before us */

	struct rwsem_waiter waiter;

	struct rw_semaphore *ret = sem;



	/* undo write bias from down_write operation, stop active locking */

	count = rwsem_atomic_update(-RWSEM_ACTIVE_WRITE_BIAS, sem);
@@ -478,7 +479,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) 
		count = rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);



	/* wait until we successfully acquire the lock */

	set_current_state(TASK_UNINTERRUPTIBLE);

	set_current_state(state);

	while (true) {

		if (rwsem_try_write_lock(count, sem))

			break;
@@ -486,21 +487,39 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) 


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

		do {

			if (signal_pending_state(state, current)) {

				raw_spin_lock_irq(&sem->wait_lock);

				ret = ERR_PTR(-EINTR);

				goto out;

			}

			schedule();

			set_current_state(TASK_UNINTERRUPTIBLE);

			set_current_state(state);

		} while ((count = sem->count) & RWSEM_ACTIVE_MASK);



		raw_spin_lock_irq(&sem->wait_lock);

	}

out:

	__set_current_state(TASK_RUNNING);



	list_del(&waiter.list);

	raw_spin_unlock_irq(&sem->wait_lock);



	return sem;

	return ret;

}



__visible struct rw_semaphore * __sched

rwsem_down_write_failed(struct rw_semaphore *sem)

{

	return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE);

}

EXPORT_SYMBOL(rwsem_down_write_failed);



__visible struct rw_semaphore * __sched

rwsem_down_write_failed_killable(struct rw_semaphore *sem)

{

	return __rwsem_down_write_failed_common(sem, TASK_KILLABLE);

}

EXPORT_SYMBOL(rwsem_down_write_failed_killable);



/*

 * handle waking up a waiter on the semaphore

 * - up_read/up_write has decremented the active part of count if we come here