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dm bufio: Add DM_BUFIO_CLIENT_NO_SLEEP flag

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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: Nathan Huckleberry <nhuck@google.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
This commit is contained in:
Nathan Huckleberry 2022-07-22 09:38:22 +00:00 committed by Mike Snitzer
parent 0fcb100d50
commit b32d45824a
2 changed files with 24 additions and 3 deletions
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22
drivers/md/dm-bufio.c
View File

@ -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;
@ -167,17 +170,26 @@ struct dm_buffer {
static void dm_bufio_lock(struct dm_bufio_client *c)
{
mutex_lock_nested(&c->lock, dm_bufio_in_request());
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)
{
return mutex_trylock(&c->lock);
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)
{
mutex_unlock(&c->lock);
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;

5
include/linux/dm-bufio.h
View File

@ -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
*/