Commit b32d4582 authored by Nathan Huckleberry's avatar Nathan Huckleberry Committed by Mike Snitzer
Browse files

dm bufio: Add DM_BUFIO_CLIENT_NO_SLEEP flag 



Add an optional flag that ensures dm_bufio_client does not sleep
(primary focus is to service dm_bufio_get without sleeping). This
allows the dm-bufio cache to be queried from interrupt context.

To ensure that dm-bufio does not sleep, dm-bufio must use a spinlock
instead of a mutex. Additionally, to avoid deadlocks, special care
must be taken so that dm-bufio does not sleep while holding the
spinlock.

But again: the scope of this no_sleep is initially confined to
dm_bufio_get, so __alloc_buffer_wait_no_callback is _not_ changed to
avoid sleeping because __bufio_new avoids allocation for NF_GET.

Signed-off-by: default avatarNathan Huckleberry <nhuck@google.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
parent 0fcb100d

drivers/md/dm-bufio.c

+19 −3
Original line number Diff line number Diff line
@@ -81,6 +81,8 @@ 
 */

struct dm_bufio_client {

	struct mutex lock;

	spinlock_t spinlock;

	unsigned long spinlock_flags;



	struct list_head lru[LIST_SIZE];

	unsigned long n_buffers[LIST_SIZE];
@@ -90,6 +92,7 @@ struct dm_bufio_client { 
	s8 sectors_per_block_bits;

	void (*alloc_callback)(struct dm_buffer *);

	void (*write_callback)(struct dm_buffer *);

	bool no_sleep;



	struct kmem_cache *slab_buffer;

	struct kmem_cache *slab_cache;
@@ -167,16 +170,25 @@ struct dm_buffer { 


static void dm_bufio_lock(struct dm_bufio_client *c)

{

	if (c->no_sleep)

		spin_lock_irqsave_nested(&c->spinlock, c->spinlock_flags, dm_bufio_in_request());

	else

		mutex_lock_nested(&c->lock, dm_bufio_in_request());

}



static int dm_bufio_trylock(struct dm_bufio_client *c)

{

	if (c->no_sleep)

		return spin_trylock_irqsave(&c->spinlock, c->spinlock_flags);

	else

		return mutex_trylock(&c->lock);

}



static void dm_bufio_unlock(struct dm_bufio_client *c)

{

	if (c->no_sleep)

		spin_unlock_irqrestore(&c->spinlock, c->spinlock_flags);

	else

		mutex_unlock(&c->lock);

}
@@ -1748,12 +1760,16 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign 
	c->alloc_callback = alloc_callback;

	c->write_callback = write_callback;



	if (flags & DM_BUFIO_CLIENT_NO_SLEEP)

		c->no_sleep = true;



	for (i = 0; i < LIST_SIZE; i++) {

		INIT_LIST_HEAD(&c->lru[i]);

		c->n_buffers[i] = 0;

	}



	mutex_init(&c->lock);

	spin_lock_init(&c->spinlock);

	INIT_LIST_HEAD(&c->reserved_buffers);

	c->need_reserved_buffers = reserved_buffers;

include/linux/dm-bufio.h

+5 −0
Original line number Diff line number Diff line
@@ -17,6 +17,11 @@ 
struct dm_bufio_client;

struct dm_buffer;



/*

 * Flags for dm_bufio_client_create

 */

#define DM_BUFIO_CLIENT_NO_SLEEP 0x1



/*

 * Create a buffered IO cache on a given device

 */