Snapshot doesn't work with realtime kernels since the commit f79ae415b64c.
hlist_bl is implemented as a raw spinlock and the code takes two non-raw
spinlocks while holding hlist_bl (non-raw spinlocks are blocking mutexes
in the realtime kernel, so they couldn't be taken inside a raw spinlock).
This patch fixes the problem by using non-raw spinlock
exception_table_lock instead of the hlist_bl lock.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Fixes: f79ae415b64c ("dm snapshot: Make exception tables scalable")
---
drivers/md/dm-snap.c | 65 ++++++++++++++++++++++++++++++++-------------------
1 file changed, 42 insertions(+), 23 deletions(-)
Index: linux-2.6/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-snap.c 2019-11-08 15:51:42.000000000 +0100
+++ linux-2.6/drivers/md/dm-snap.c 2019-11-08 15:54:58.000000000 +0100
@@ -141,6 +141,10 @@ struct dm_snapshot {
* for them to be committed.
*/
struct bio_list bios_queued_during_merge;
+
+#ifdef CONFIG_PREEMPT_RT_BASE
+ spinlock_t exception_table_lock;
+#endif
};
/*
@@ -625,30 +629,42 @@ static uint32_t exception_hash(struct dm
/* Lock to protect access to the completed and pending exception hash tables. */
struct dm_exception_table_lock {
+#ifndef CONFIG_PREEMPT_RT_BASE
struct hlist_bl_head *complete_slot;
struct hlist_bl_head *pending_slot;
+#endif
};
static void dm_exception_table_lock_init(struct dm_snapshot *s, chunk_t chunk,
struct dm_exception_table_lock *lock)
{
+#ifndef CONFIG_PREEMPT_RT_BASE
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)];
+#endif
}
-static void dm_exception_table_lock(struct dm_exception_table_lock *lock)
+static void dm_exception_table_lock(struct dm_snapshot *s, struct dm_exception_table_lock *lock)
{
+#ifdef CONFIG_PREEMPT_RT_BASE
+ spin_lock(&s->exception_table_lock);
+#else
hlist_bl_lock(lock->complete_slot);
hlist_bl_lock(lock->pending_slot);
+#endif
}
-static void dm_exception_table_unlock(struct dm_exception_table_lock *lock)
+static void dm_exception_table_unlock(struct dm_snapshot *s, struct dm_exception_table_lock *lock)
{
+#ifdef CONFIG_PREEMPT_RT_BASE
+ spin_unlock(&s->exception_table_lock);
+#else
hlist_bl_unlock(lock->pending_slot);
hlist_bl_unlock(lock->complete_slot);
+#endif
}
static int dm_exception_table_init(struct dm_exception_table *et,
@@ -835,9 +851,9 @@ static int dm_add_exception(void *contex
*/
dm_exception_table_lock_init(s, old, &lock);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
dm_insert_exception(&s->complete, e);
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
return 0;
}
@@ -1318,6 +1334,9 @@ static int snapshot_ctr(struct dm_target
s->first_merging_chunk = 0;
s->num_merging_chunks = 0;
bio_list_init(&s->bios_queued_during_merge);
+#ifdef CONFIG_PREEMPT_RT_BASE
+ spin_lock_init(&s->exception_table_lock);
+#endif
/* Allocate hash table for COW data */
if (init_hash_tables(s)) {
@@ -1651,7 +1670,7 @@ static void pending_complete(void *conte
invalidate_snapshot(s, -EIO);
error = 1;
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
goto out;
}
@@ -1660,13 +1679,13 @@ static void pending_complete(void *conte
invalidate_snapshot(s, -ENOMEM);
error = 1;
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
goto out;
}
*e = pe->e;
down_read(&s->lock);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
if (!s->valid) {
up_read(&s->lock);
free_completed_exception(e);
@@ -1687,16 +1706,16 @@ static void pending_complete(void *conte
/* Wait for conflicting reads to drain */
if (__chunk_is_tracked(s, pe->e.old_chunk)) {
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
__check_for_conflicting_io(s, pe->e.old_chunk);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
}
out:
/* Remove the in-flight exception from the list */
dm_remove_exception(&pe->e);
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
snapshot_bios = bio_list_get(&pe->snapshot_bios);
origin_bios = bio_list_get(&pe->origin_bios);
@@ -1968,7 +1987,7 @@ static int snapshot_map(struct dm_target
}
down_read(&s->lock);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
if (!s->valid || (unlikely(s->snapshot_overflowed) &&
bio_data_dir(bio) == WRITE)) {
@@ -1997,7 +2016,7 @@ static int snapshot_map(struct dm_target
remap_exception(s, e, bio, chunk);
if (unlikely(bio_op(bio) == REQ_OP_DISCARD) &&
io_overlaps_chunk(s, bio)) {
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
up_read(&s->lock);
zero_exception(s, e, bio, chunk);
r = DM_MAPIO_SUBMITTED; /* discard is not issued */
@@ -2024,9 +2043,9 @@ static int snapshot_map(struct dm_target
if (bio_data_dir(bio) == WRITE) {
pe = __lookup_pending_exception(s, chunk);
if (!pe) {
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
pe = alloc_pending_exception(s);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(s, &lock);
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
@@ -2037,7 +2056,7 @@ static int snapshot_map(struct dm_target
pe = __find_pending_exception(s, pe, chunk);
if (!pe) {
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
up_read(&s->lock);
down_write(&s->lock);
@@ -2063,7 +2082,7 @@ static int snapshot_map(struct dm_target
if (!pe->started && io_overlaps_chunk(s, bio)) {
pe->started = 1;
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
up_read(&s->lock);
start_full_bio(pe, bio);
@@ -2076,7 +2095,7 @@ static int snapshot_map(struct dm_target
/* this is protected by the exception table lock */
pe->started = 1;
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
up_read(&s->lock);
start_copy(pe);
@@ -2088,7 +2107,7 @@ static int snapshot_map(struct dm_target
}
out_unlock:
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(s, &lock);
up_read(&s->lock);
out:
return r;
@@ -2449,7 +2468,7 @@ static int __origin_write(struct list_he
dm_exception_table_lock_init(snap, chunk, &lock);
down_read(&snap->lock);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(snap, &lock);
/* Only deal with valid and active snapshots */
if (!snap->valid || !snap->active)
@@ -2466,9 +2485,9 @@ static int __origin_write(struct list_he
if (e)
goto next_snapshot;
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(snap, &lock);
pe = alloc_pending_exception(snap);
- dm_exception_table_lock(&lock);
+ dm_exception_table_lock(snap, &lock);
pe2 = __lookup_pending_exception(snap, chunk);
@@ -2481,7 +2500,7 @@ static int __origin_write(struct list_he
pe = __insert_pending_exception(snap, pe, chunk);
if (!pe) {
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(snap, &lock);
up_read(&snap->lock);
invalidate_snapshot(snap, -ENOMEM);
@@ -2516,7 +2535,7 @@ static int __origin_write(struct list_he
}
next_snapshot:
- dm_exception_table_unlock(&lock);
+ dm_exception_table_unlock(snap, &lock);
up_read(&snap->lock);
if (pe_to_start_now) {
--
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