From b32d45824aa7e07a0c3257a16e3a2a691b11b39a Mon Sep 17 00:00:00 2001 From: Nathan Huckleberry Date: Fri, 22 Jul 2022 09:38:22 +0000 Subject: 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: Nathan Huckleberry Signed-off-by: Mike Snitzer --- drivers/md/dm-bufio.c | 22 +++++++++++++++++++--- include/linux/dm-bufio.h | 5 +++++ 2 files changed, 24 insertions(+), 3 deletions(-) diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index ad5603eb12e3..486179d1831c 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -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; diff --git a/include/linux/dm-bufio.h b/include/linux/dm-bufio.h index e21480715255..15d9e15ca830 100644 --- a/include/linux/dm-bufio.h +++ b/include/linux/dm-bufio.h @@ -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 */ -- cgit v1.2.3-59-g8ed1b