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dm-bufio: fix no-sleep mode
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dm-bufio has a no-sleep mode. When activated (with the
DM_BUFIO_CLIENT_NO_SLEEP flag), the bufio client is read-only and we
could call dm_bufio_get from tasklets. This is used by dm-verity.

Unfortunately, commit 450e8de ("dm bufio: improve concurrent IO
performance") broke this and the kernel would warn that cache_get()
was calling down_read() from no-sleeping context. The bug can be
reproduced by using "veritysetup open" with the "--use-tasklets"
flag.

This commit fixes dm-bufio, so that the tasklet mode works again, by
expanding use of the 'no_sleep_enabled' static_key to conditionally
use either a rw_semaphore or rwlock_t (which are colocated in the
buffer_tree structure using a union).

Signed-off-by: Mikulas Patocka <[email protected]>
Cc: [email protected]	# v6.4
Fixes: 450e8de ("dm bufio: improve concurrent IO performance")
Signed-off-by: Mike Snitzer <[email protected]>
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Mikulas Patocka authored and Mike Snitzer committed Nov 17, 2023
1 parent ccadc8a commit 2a69506
Showing 1 changed file with 62 additions and 25 deletions.
87 changes: 62 additions & 25 deletions drivers/md/dm-bufio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -254,7 +254,7 @@ enum evict_result {

typedef enum evict_result (*le_predicate)(struct lru_entry *le, void *context);

static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *context)
static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *context, bool no_sleep)
{
unsigned long tested = 0;
struct list_head *h = lru->cursor;
Expand Down Expand Up @@ -295,7 +295,8 @@ static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *con

h = h->next;

cond_resched();
if (!no_sleep)
cond_resched();
}

return NULL;
Expand Down Expand Up @@ -382,7 +383,10 @@ struct dm_buffer {
*/

struct buffer_tree {
struct rw_semaphore lock;
union {
struct rw_semaphore lock;
rwlock_t spinlock;
} u;
struct rb_root root;
} ____cacheline_aligned_in_smp;

Expand All @@ -393,32 +397,47 @@ struct dm_buffer_cache {
* on the locks.
*/
unsigned int num_locks;
bool no_sleep;
struct buffer_tree trees[];
};

static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);

static inline unsigned int cache_index(sector_t block, unsigned int num_locks)
{
return dm_hash_locks_index(block, num_locks);
}

static inline void cache_read_lock(struct dm_buffer_cache *bc, sector_t block)
{
down_read(&bc->trees[cache_index(block, bc->num_locks)].lock);
if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
read_lock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
else
down_read(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
}

static inline void cache_read_unlock(struct dm_buffer_cache *bc, sector_t block)
{
up_read(&bc->trees[cache_index(block, bc->num_locks)].lock);
if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
read_unlock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
else
up_read(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
}

static inline void cache_write_lock(struct dm_buffer_cache *bc, sector_t block)
{
down_write(&bc->trees[cache_index(block, bc->num_locks)].lock);
if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
write_lock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
else
down_write(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
}

static inline void cache_write_unlock(struct dm_buffer_cache *bc, sector_t block)
{
up_write(&bc->trees[cache_index(block, bc->num_locks)].lock);
if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
write_unlock_bh(&bc->trees[cache_index(block, bc->num_locks)].u.spinlock);
else
up_write(&bc->trees[cache_index(block, bc->num_locks)].u.lock);
}

/*
Expand All @@ -442,18 +461,32 @@ static void lh_init(struct lock_history *lh, struct dm_buffer_cache *cache, bool

static void __lh_lock(struct lock_history *lh, unsigned int index)
{
if (lh->write)
down_write(&lh->cache->trees[index].lock);
else
down_read(&lh->cache->trees[index].lock);
if (lh->write) {
if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
write_lock_bh(&lh->cache->trees[index].u.spinlock);
else
down_write(&lh->cache->trees[index].u.lock);
} else {
if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
read_lock_bh(&lh->cache->trees[index].u.spinlock);
else
down_read(&lh->cache->trees[index].u.lock);
}
}

static void __lh_unlock(struct lock_history *lh, unsigned int index)
{
if (lh->write)
up_write(&lh->cache->trees[index].lock);
else
up_read(&lh->cache->trees[index].lock);
if (lh->write) {
if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
write_unlock_bh(&lh->cache->trees[index].u.spinlock);
else
up_write(&lh->cache->trees[index].u.lock);
} else {
if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
read_unlock_bh(&lh->cache->trees[index].u.spinlock);
else
up_read(&lh->cache->trees[index].u.lock);
}
}

/*
Expand Down Expand Up @@ -502,14 +535,18 @@ static struct dm_buffer *list_to_buffer(struct list_head *l)
return le_to_buffer(le);
}

static void cache_init(struct dm_buffer_cache *bc, unsigned int num_locks)
static void cache_init(struct dm_buffer_cache *bc, unsigned int num_locks, bool no_sleep)
{
unsigned int i;

bc->num_locks = num_locks;
bc->no_sleep = no_sleep;

for (i = 0; i < bc->num_locks; i++) {
init_rwsem(&bc->trees[i].lock);
if (no_sleep)
rwlock_init(&bc->trees[i].u.spinlock);
else
init_rwsem(&bc->trees[i].u.lock);
bc->trees[i].root = RB_ROOT;
}

Expand Down Expand Up @@ -648,7 +685,7 @@ static struct dm_buffer *__cache_evict(struct dm_buffer_cache *bc, int list_mode
struct lru_entry *le;
struct dm_buffer *b;

le = lru_evict(&bc->lru[list_mode], __evict_pred, &w);
le = lru_evict(&bc->lru[list_mode], __evict_pred, &w, bc->no_sleep);
if (!le)
return NULL;

Expand Down Expand Up @@ -702,7 +739,7 @@ static void __cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_
struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};

while (true) {
le = lru_evict(&bc->lru[old_mode], __evict_pred, &w);
le = lru_evict(&bc->lru[old_mode], __evict_pred, &w, bc->no_sleep);
if (!le)
break;

Expand Down Expand Up @@ -915,10 +952,11 @@ static void cache_remove_range(struct dm_buffer_cache *bc,
{
unsigned int i;

BUG_ON(bc->no_sleep);
for (i = 0; i < bc->num_locks; i++) {
down_write(&bc->trees[i].lock);
down_write(&bc->trees[i].u.lock);
__remove_range(bc, &bc->trees[i].root, begin, end, pred, release);
up_write(&bc->trees[i].lock);
up_write(&bc->trees[i].u.lock);
}
}

Expand Down Expand Up @@ -979,8 +1017,6 @@ struct dm_bufio_client {
struct dm_buffer_cache cache; /* must be last member */
};

static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);

/*----------------------------------------------------------------*/

#define dm_bufio_in_request() (!!current->bio_list)
Expand Down Expand Up @@ -1871,7 +1907,8 @@ static void *new_read(struct dm_bufio_client *c, sector_t block,
if (need_submit)
submit_io(b, REQ_OP_READ, read_endio);

wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
if (nf != NF_GET) /* we already tested this condition above */
wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);

if (b->read_error) {
int error = blk_status_to_errno(b->read_error);
Expand Down Expand Up @@ -2421,7 +2458,7 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
r = -ENOMEM;
goto bad_client;
}
cache_init(&c->cache, num_locks);
cache_init(&c->cache, num_locks, (flags & DM_BUFIO_CLIENT_NO_SLEEP) != 0);

c->bdev = bdev;
c->block_size = block_size;
Expand Down

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