Skip to content

Commit

Permalink
rhashtable: Allow rhashtable to be used from irq-safe contexts
Browse files Browse the repository at this point in the history 
rhashtable currently only does bh-safe synchronization making it impossible
to use from irq-safe contexts. Switch it to use irq-safe synchronization to
remove the restriction.

v2: Update the lock functions to return the ulong flags value and unlock
    functions to take the value directly instead of passing around the
    pointer. Suggested by Linus.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: David Vernet <dvernet@meta.com>
Acked-by: Josh Don <joshdon@google.com>
Acked-by: Hao Luo <haoluo@google.com>
Acked-by: Barret Rhoden <brho@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
  • Loading branch information
@htejun @davem330
htejun authored and davem330 committed Dec 9, 2022
1 parent b602d00 commit e47877c
Show file tree
Hide file tree
Showing 2 changed files with 46 additions and 31 deletions.
61 changes: 36 additions & 25 deletions include/linux/rhashtable.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -323,29 +323,36 @@ static inline struct rhash_lock_head __rcu **rht_bucket_insert(
* When we write to a bucket without unlocking, we use rht_assign_locked().
*/

static inline void rht_lock(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bkt)
static inline unsigned long rht_lock(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bkt)
{
local_bh_disable();
unsigned long flags;

local_irq_save(flags);
bit_spin_lock(0, (unsigned long *)bkt);
lock_map_acquire(&tbl->dep_map);
return flags;
}

static inline void rht_lock_nested(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bucket,
unsigned int subclass)
static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bucket,
unsigned int subclass)
{
local_bh_disable();
unsigned long flags;

local_irq_save(flags);
bit_spin_lock(0, (unsigned long *)bucket);
lock_acquire_exclusive(&tbl->dep_map, subclass, 0, NULL, _THIS_IP_);
return flags;
}

static inline void rht_unlock(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bkt)
struct rhash_lock_head __rcu **bkt,
unsigned long flags)
{
lock_map_release(&tbl->dep_map);
bit_spin_unlock(0, (unsigned long *)bkt);
local_bh_enable();
local_irq_restore(flags);
}

static inline struct rhash_head *__rht_ptr(
Expand Down Expand Up @@ -393,15 +400,16 @@ static inline void rht_assign_locked(struct rhash_lock_head __rcu **bkt,

static inline void rht_assign_unlock(struct bucket_table *tbl,
struct rhash_lock_head __rcu **bkt,
struct rhash_head *obj)
struct rhash_head *obj,
unsigned long flags)
{
if (rht_is_a_nulls(obj))
obj = NULL;
lock_map_release(&tbl->dep_map);
rcu_assign_pointer(*bkt, (void *)obj);
preempt_enable();
__release(bitlock);
local_bh_enable();
local_irq_restore(flags);
}

/**
Expand Down Expand Up @@ -706,6 +714,7 @@ static inline void *__rhashtable_insert_fast(
struct rhash_head __rcu **pprev;
struct bucket_table *tbl;
struct rhash_head *head;
unsigned long flags;
unsigned int hash;
int elasticity;
void *data;
Expand All @@ -720,11 +729,11 @@ static inline void *__rhashtable_insert_fast(
if (!bkt)
goto out;
pprev = NULL;
rht_lock(tbl, bkt);
flags = rht_lock(tbl, bkt);

if (unlikely(rcu_access_pointer(tbl->future_tbl))) {
slow_path:
rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
rcu_read_unlock();
return rhashtable_insert_slow(ht, key, obj);
}
Expand Down Expand Up @@ -756,9 +765,9 @@ static inline void *__rhashtable_insert_fast(
RCU_INIT_POINTER(list->rhead.next, head);
if (pprev) {
rcu_assign_pointer(*pprev, obj);
rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
} else
rht_assign_unlock(tbl, bkt, obj);
rht_assign_unlock(tbl, bkt, obj, flags);
data = NULL;
goto out;
}
Expand All @@ -785,7 +794,7 @@ static inline void *__rhashtable_insert_fast(
}

atomic_inc(&ht->nelems);
rht_assign_unlock(tbl, bkt, obj);
rht_assign_unlock(tbl, bkt, obj, flags);

if (rht_grow_above_75(ht, tbl))
schedule_work(&ht->run_work);
Expand All @@ -797,7 +806,7 @@ static inline void *__rhashtable_insert_fast(
return data;

out_unlock:
rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
goto out;
}

Expand Down Expand Up @@ -991,6 +1000,7 @@ static inline int __rhashtable_remove_fast_one(
struct rhash_lock_head __rcu **bkt;
struct rhash_head __rcu **pprev;
struct rhash_head *he;
unsigned long flags;
unsigned int hash;
int err = -ENOENT;

Expand All @@ -999,7 +1009,7 @@ static inline int __rhashtable_remove_fast_one(
if (!bkt)
return -ENOENT;
pprev = NULL;
rht_lock(tbl, bkt);
flags = rht_lock(tbl, bkt);

rht_for_each_from(he, rht_ptr(bkt, tbl, hash), tbl, hash) {
struct rhlist_head *list;
Expand Down Expand Up @@ -1043,14 +1053,14 @@ static inline int __rhashtable_remove_fast_one(

if (pprev) {
rcu_assign_pointer(*pprev, obj);
rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
} else {
rht_assign_unlock(tbl, bkt, obj);
rht_assign_unlock(tbl, bkt, obj, flags);
}
goto unlocked;
}

rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
unlocked:
if (err > 0) {
atomic_dec(&ht->nelems);
Expand Down Expand Up @@ -1143,6 +1153,7 @@ static inline int __rhashtable_replace_fast(
struct rhash_lock_head __rcu **bkt;
struct rhash_head __rcu **pprev;
struct rhash_head *he;
unsigned long flags;
unsigned int hash;
int err = -ENOENT;

Expand All @@ -1158,7 +1169,7 @@ static inline int __rhashtable_replace_fast(
return -ENOENT;

pprev = NULL;
rht_lock(tbl, bkt);
flags = rht_lock(tbl, bkt);

rht_for_each_from(he, rht_ptr(bkt, tbl, hash), tbl, hash) {
if (he != obj_old) {
Expand All @@ -1169,15 +1180,15 @@ static inline int __rhashtable_replace_fast(
rcu_assign_pointer(obj_new->next, obj_old->next);
if (pprev) {
rcu_assign_pointer(*pprev, obj_new);
rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
} else {
rht_assign_unlock(tbl, bkt, obj_new);
rht_assign_unlock(tbl, bkt, obj_new, flags);
}
err = 0;
goto unlocked;
}

rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);

unlocked:
return err;
Expand Down
16 changes: 10 additions & 6 deletions lib/rhashtable.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -231,6 +231,7 @@ static int rhashtable_rehash_one(struct rhashtable *ht,
struct rhash_head *head, *next, *entry;
struct rhash_head __rcu **pprev = NULL;
unsigned int new_hash;
unsigned long flags;

if (new_tbl->nest)
goto out;
Expand All @@ -253,13 +254,14 @@ static int rhashtable_rehash_one(struct rhashtable *ht,

new_hash = head_hashfn(ht, new_tbl, entry);

rht_lock_nested(new_tbl, &new_tbl->buckets[new_hash], SINGLE_DEPTH_NESTING);
flags = rht_lock_nested(new_tbl, &new_tbl->buckets[new_hash],
SINGLE_DEPTH_NESTING);

head = rht_ptr(new_tbl->buckets + new_hash, new_tbl, new_hash);

RCU_INIT_POINTER(entry->next, head);

rht_assign_unlock(new_tbl, &new_tbl->buckets[new_hash], entry);
rht_assign_unlock(new_tbl, &new_tbl->buckets[new_hash], entry, flags);

if (pprev)
rcu_assign_pointer(*pprev, next);
Expand All @@ -276,18 +278,19 @@ static int rhashtable_rehash_chain(struct rhashtable *ht,
{
struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
struct rhash_lock_head __rcu **bkt = rht_bucket_var(old_tbl, old_hash);
unsigned long flags;
int err;

if (!bkt)
return 0;
rht_lock(old_tbl, bkt);
flags = rht_lock(old_tbl, bkt);

while (!(err = rhashtable_rehash_one(ht, bkt, old_hash)))
;

if (err == -ENOENT)
err = 0;
rht_unlock(old_tbl, bkt);
rht_unlock(old_tbl, bkt, flags);

return err;
}
Expand Down Expand Up @@ -590,6 +593,7 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
struct bucket_table *new_tbl;
struct bucket_table *tbl;
struct rhash_lock_head __rcu **bkt;
unsigned long flags;
unsigned int hash;
void *data;

Expand All @@ -607,15 +611,15 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
data = ERR_PTR(-EAGAIN);
} else {
rht_lock(tbl, bkt);
flags = rht_lock(tbl, bkt);
data = rhashtable_lookup_one(ht, bkt, tbl,
hash, key, obj);
new_tbl = rhashtable_insert_one(ht, bkt, tbl,
hash, obj, data);
if (PTR_ERR(new_tbl) != -EEXIST)
data = ERR_CAST(new_tbl);

rht_unlock(tbl, bkt);
rht_unlock(tbl, bkt, flags);
}
} while (!IS_ERR_OR_NULL(new_tbl));

Expand Down

0 comments on commit e47877c

Please sign in to comment.