Commit 8581b19eb2c5 for kernel
commit 8581b19eb2c5ccf06c195d3b5468c3c9d17a5020
Author: Mikulas Patocka <mpatocka@redhat.com>
Date: Mon Dec 1 22:13:10 2025 +0100
dm-snapshot: fix 'scheduling while atomic' on real-time kernels
There is reported 'scheduling while atomic' bug when using dm-snapshot on
real-time kernels. The reason for the bug is that the hlist_bl code does
preempt_disable() when taking the lock and the kernel attempts to take
other spinlocks while holding the hlist_bl lock.
Fix this by converting a hlist_bl spinlock into a regular spinlock.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reported-by: Jiping Ma <jiping.ma2@windriver.com>
diff --git a/drivers/md/dm-exception-store.h b/drivers/md/dm-exception-store.h
index b67976637538..061b4d310813 100644
--- a/drivers/md/dm-exception-store.h
+++ b/drivers/md/dm-exception-store.h
@@ -29,7 +29,7 @@ typedef sector_t chunk_t;
* chunk within the device.
*/
struct dm_exception {
- struct hlist_bl_node hash_list;
+ struct hlist_node hash_list;
chunk_t old_chunk;
chunk_t new_chunk;
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index f40c18da4000..dbd148967de4 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -40,10 +40,15 @@ static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
(DM_TRACKED_CHUNK_HASH_SIZE - 1))
+struct dm_hlist_head {
+ struct hlist_head head;
+ spinlock_t lock;
+};
+
struct dm_exception_table {
uint32_t hash_mask;
unsigned int hash_shift;
- struct hlist_bl_head *table;
+ struct dm_hlist_head *table;
};
struct dm_snapshot {
@@ -628,8 +633,8 @@ static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk);
/* Lock to protect access to the completed and pending exception hash tables. */
struct dm_exception_table_lock {
- struct hlist_bl_head *complete_slot;
- struct hlist_bl_head *pending_slot;
+ spinlock_t *complete_slot;
+ spinlock_t *pending_slot;
};
static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk,
@@ -638,20 +643,20 @@ static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk,
struct dm_exception_table *complete = &s->complete;
struct dm_exception_table *pending = &s->pending;
- lock->complete_slot = &complete->table[exception_hash(complete, chunk)];
- lock->pending_slot = &pending->table[exception_hash(pending, chunk)];
+ lock->complete_slot = &complete->table[exception_hash(complete, chunk)].lock;
+ lock->pending_slot = &pending->table[exception_hash(pending, chunk)].lock;
}
static void dm_exception_table_lock(struct dm_exception_table_lock *lock)
{
- hlist_bl_lock(lock->complete_slot);
- hlist_bl_lock(lock->pending_slot);
+ spin_lock_nested(lock->complete_slot, 1);
+ spin_lock_nested(lock->pending_slot, 2);
}
static void dm_exception_table_unlock(struct dm_exception_table_lock *lock)
{
- hlist_bl_unlock(lock->pending_slot);
- hlist_bl_unlock(lock->complete_slot);
+ spin_unlock(lock->pending_slot);
+ spin_unlock(lock->complete_slot);
}
static int dm_exception_table_init(struct dm_exception_table *et,
@@ -661,13 +666,15 @@ static int dm_exception_table_init(struct dm_exception_table *et,
et->hash_shift = hash_shift;
et->hash_mask = size - 1;
- et->table = kvmalloc_array(size, sizeof(struct hlist_bl_head),
+ et->table = kvmalloc_array(size, sizeof(struct dm_hlist_head),
GFP_KERNEL);
if (!et->table)
return -ENOMEM;
- for (i = 0; i < size; i++)
- INIT_HLIST_BL_HEAD(et->table + i);
+ for (i = 0; i < size; i++) {
+ INIT_HLIST_HEAD(&et->table[i].head);
+ spin_lock_init(&et->table[i].lock);
+ }
return 0;
}
@@ -675,16 +682,17 @@ static int dm_exception_table_init(struct dm_exception_table *et,
static void dm_exception_table_exit(struct dm_exception_table *et,
struct kmem_cache *mem)
{
- struct hlist_bl_head *slot;
+ struct dm_hlist_head *slot;
struct dm_exception *ex;
- struct hlist_bl_node *pos, *n;
+ struct hlist_node *pos;
int i, size;
size = et->hash_mask + 1;
for (i = 0; i < size; i++) {
slot = et->table + i;
- hlist_bl_for_each_entry_safe(ex, pos, n, slot, hash_list) {
+ hlist_for_each_entry_safe(ex, pos, &slot->head, hash_list) {
+ hlist_del(&ex->hash_list);
kmem_cache_free(mem, ex);
cond_resched();
}
@@ -700,7 +708,7 @@ static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
static void dm_remove_exception(struct dm_exception *e)
{
- hlist_bl_del(&e->hash_list);
+ hlist_del(&e->hash_list);
}
/*
@@ -710,12 +718,11 @@ static void dm_remove_exception(struct dm_exception *e)
static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
chunk_t chunk)
{
- struct hlist_bl_head *slot;
- struct hlist_bl_node *pos;
+ struct hlist_head *slot;
struct dm_exception *e;
- slot = &et->table[exception_hash(et, chunk)];
- hlist_bl_for_each_entry(e, pos, slot, hash_list)
+ slot = &et->table[exception_hash(et, chunk)].head;
+ hlist_for_each_entry(e, slot, hash_list)
if (chunk >= e->old_chunk &&
chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
return e;
@@ -762,18 +769,17 @@ static void free_pending_exception(struct dm_snap_pending_exception *pe)
static void dm_insert_exception(struct dm_exception_table *eh,
struct dm_exception *new_e)
{
- struct hlist_bl_head *l;
- struct hlist_bl_node *pos;
+ struct hlist_head *l;
struct dm_exception *e = NULL;
- l = &eh->table[exception_hash(eh, new_e->old_chunk)];
+ l = &eh->table[exception_hash(eh, new_e->old_chunk)].head;
/* Add immediately if this table doesn't support consecutive chunks */
if (!eh->hash_shift)
goto out;
/* List is ordered by old_chunk */
- hlist_bl_for_each_entry(e, pos, l, hash_list) {
+ hlist_for_each_entry(e, l, hash_list) {
/* Insert after an existing chunk? */
if (new_e->old_chunk == (e->old_chunk +
dm_consecutive_chunk_count(e) + 1) &&
@@ -804,13 +810,13 @@ static void dm_insert_exception(struct dm_exception_table *eh,
* Either the table doesn't support consecutive chunks or slot
* l is empty.
*/
- hlist_bl_add_head(&new_e->hash_list, l);
+ hlist_add_head(&new_e->hash_list, l);
} else if (new_e->old_chunk < e->old_chunk) {
/* Add before an existing exception */
- hlist_bl_add_before(&new_e->hash_list, &e->hash_list);
+ hlist_add_before(&new_e->hash_list, &e->hash_list);
} else {
/* Add to l's tail: e is the last exception in this slot */
- hlist_bl_add_behind(&new_e->hash_list, &e->hash_list);
+ hlist_add_behind(&new_e->hash_list, &e->hash_list);
}
}
@@ -820,7 +826,6 @@ static void dm_insert_exception(struct dm_exception_table *eh,
*/
static int dm_add_exception(void *context, chunk_t old, chunk_t new)
{
- struct dm_exception_table_lock lock;
struct dm_snapshot *s = context;
struct dm_exception *e;
@@ -833,17 +838,7 @@ static int dm_add_exception(void *context, chunk_t old, chunk_t new)
/* Consecutive_count is implicitly initialised to zero */
e->new_chunk = new;
- /*
- * Although there is no need to lock access to the exception tables
- * here, if we don't then hlist_bl_add_head(), called by
- * dm_insert_exception(), will complain about accessing the
- * corresponding list without locking it first.
- */
- dm_exception_table_lock_init(s, old, &lock);
-
- dm_exception_table_lock(&lock);
dm_insert_exception(&s->complete, e);
- dm_exception_table_unlock(&lock);
return 0;
}
@@ -873,7 +868,7 @@ static int calc_max_buckets(void)
/* use a fixed size of 2MB */
unsigned long mem = 2 * 1024 * 1024;
- mem /= sizeof(struct hlist_bl_head);
+ mem /= sizeof(struct dm_hlist_head);
return mem;
}