The md->bs bioset currently needs the BIOSET_NEED_RESCUER flag
which I hope to deprecate. It is currently needed because
__split_and_process_bio() can potentially allocate from the
bioset multiple times within the one make_request_fn context.
Subsequent allocations can deadlock waiting for the bio returned
by the first allocation to complete - but it is stuck on the
current->bio_list list.
The bioset is also used in setup_clone() in dm-rq.c, but there a
non-blocking (GFP_ATOMIC) allocation is used, so there is no risk of
deadlock.
dm also provide rescuing for ->map() calls. If a map call ever blocks,
any bios already submitted with generic_make_request() will be passed to
the bioset rescuer thread.
This patch unifies these two separate needs for rescuing bios into a
single mechanism, and use the md->wq work queue to do the rescuing.
A blk_plug_cb is added to 'struct clone_info' so that it is available
throughout the __split_and_process_bio() process.
Prior to allocating from the bioset, or calling ->map(),
dm_offload_check() is called to ensure that the blk_plug_cb is active.
If either of these operation schedules, the callback is called,
and any queued bios get passed to the wq.
Note that only current->bio_list[0] is offloaded. current->bio_list[1]
contains bios that were scheduled *before* the current one started, so
they must have been submitted from higher up the stack, and we cannot be
waiting for them here. Also, we now rescue *all* bios on the list as
there is nothing to be gained by being more selective.
This allows us to remove BIOSET_NEED_RESCUER when allocating this
bioset.
It also keeps all the mechanics of rescuing inside dm, so dm can
be in full control.
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
---
Hi,
I have only tested this lightly as I don't have any test infrastructure
for dm and don't know how to reproduce the expected deadlocks.
I'm keen to know your thoughts on this approach if you find a few spare
moment to have a look.
Thanks,
NeilBrown
drivers/md/dm-core.h | 1 +
drivers/md/dm.c | 99 ++++++++++++++++++++++++++--------------------------
2 files changed, 51 insertions(+), 49 deletions(-)
diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index 24eddbdf2ab4..cb060dd6d3ca 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -71,6 +71,7 @@ struct mapped_device {
struct work_struct work;
spinlock_t deferred_lock;
struct bio_list deferred;
+ struct bio_list rescued;
/*
* Event handling.
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 2edbcc2d7d3f..774dd71cb49a 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1134,65 +1134,63 @@ void dm_remap_zone_report(struct dm_target *ti, struct bio *bio, sector_t start)
}
EXPORT_SYMBOL_GPL(dm_remap_zone_report);
+struct clone_info {
+ struct mapped_device *md;
+ struct dm_table *map;
+ struct bio *bio;
+ struct dm_io *io;
+ sector_t sector;
+ unsigned sector_count;
+ struct blk_plug plug;
+ struct blk_plug_cb cb;
+};
+
/*
* Flush current->bio_list when the target map method blocks.
* This fixes deadlocks in snapshot and possibly in other targets.
*/
-struct dm_offload {
- struct blk_plug plug;
- struct blk_plug_cb cb;
-};
static void flush_current_bio_list(struct blk_plug_cb *cb, bool from_schedule)
{
- struct dm_offload *o = container_of(cb, struct dm_offload, cb);
+ struct clone_info *ci = container_of(cb, struct clone_info, cb);
struct bio_list list;
- struct bio *bio;
- int i;
- INIT_LIST_HEAD(&o->cb.list);
+ INIT_LIST_HEAD(&cb->list);
- if (unlikely(!current->bio_list))
+ if (unlikely(!current->bio_list || bio_list_empty(¤t->bio_list[0])))
return;
- for (i = 0; i < 2; i++) {
- list = current->bio_list[i];
- bio_list_init(¤t->bio_list[i]);
-
- while ((bio = bio_list_pop(&list))) {
- struct bio_set *bs = bio->bi_pool;
- if (unlikely(!bs) || bs == fs_bio_set ||
- !bs->rescue_workqueue) {
- bio_list_add(¤t->bio_list[i], bio);
- continue;
- }
+ list = current->bio_list[0];
+ bio_list_init(¤t->bio_list[0]);
+ spin_lock(&ci->md->deferred_lock);
+ bio_list_merge(&ci->md->rescued, &list);
+ spin_unlock(&ci->md->deferred_lock);
+ queue_work(ci->md->wq, &ci->md->work);
+}
- spin_lock(&bs->rescue_lock);
- bio_list_add(&bs->rescue_list, bio);
- queue_work(bs->rescue_workqueue, &bs->rescue_work);
- spin_unlock(&bs->rescue_lock);
- }
- }
+static void dm_offload_start(struct clone_info *ci)
+{
+ blk_start_plug(&ci->plug);
+ INIT_LIST_HEAD(&ci->cb.list);
+ ci->cb.callback = flush_current_bio_list;
}
-static void dm_offload_start(struct dm_offload *o)
+static void dm_offload_end(struct clone_info *ci)
{
- blk_start_plug(&o->plug);
- o->cb.callback = flush_current_bio_list;
- list_add(&o->cb.list, ¤t->plug->cb_list);
+ list_del(&ci->cb.list);
+ blk_finish_plug(&ci->plug);
}
-static void dm_offload_end(struct dm_offload *o)
+static void dm_offload_check(struct clone_info *ci)
{
- list_del(&o->cb.list);
- blk_finish_plug(&o->plug);
+ if (list_empty(&ci->cb.list))
+ list_add(&ci->cb.list, ¤t->plug->cb_list);
}
-static void __map_bio(struct dm_target_io *tio)
+static void __map_bio(struct clone_info *ci, struct dm_target_io *tio)
{
int r;
sector_t sector;
- struct dm_offload o;
struct bio *clone = &tio->clone;
struct dm_target *ti = tio->ti;
@@ -1206,9 +1204,8 @@ static void __map_bio(struct dm_target_io *tio)
atomic_inc(&tio->io->io_count);
sector = clone->bi_iter.bi_sector;
- dm_offload_start(&o);
+ dm_offload_check(ci);
r = ti->type->map(ti, clone);
- dm_offload_end(&o);
switch (r) {
case DM_MAPIO_SUBMITTED:
@@ -1233,15 +1230,6 @@ static void __map_bio(struct dm_target_io *tio)
}
}
-struct clone_info {
- struct mapped_device *md;
- struct dm_table *map;
- struct bio *bio;
- struct dm_io *io;
- sector_t sector;
- unsigned sector_count;
-};
-
static void bio_setup_sector(struct bio *bio, sector_t sector, unsigned len)
{
bio->bi_iter.bi_sector = sector;
@@ -1291,6 +1279,7 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci,
struct dm_target_io *tio;
struct bio *clone;
+ dm_offload_check(ci);
clone = bio_alloc_bioset(GFP_NOIO, 0, ci->md->bs);
tio = container_of(clone, struct dm_target_io, clone);
@@ -1314,7 +1303,7 @@ static void __clone_and_map_simple_bio(struct clone_info *ci,
if (len)
bio_setup_sector(clone, ci->sector, *len);
- __map_bio(tio);
+ __map_bio(ci, tio);
}
static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
@@ -1361,7 +1350,7 @@ static int __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
free_tio(tio);
break;
}
- __map_bio(tio);
+ __map_bio(ci, tio);
}
return r;
@@ -1493,6 +1482,7 @@ static void __split_and_process_bio(struct mapped_device *md,
bio_io_error(bio);
return;
}
+ dm_offload_start(&ci);
ci.map = map;
ci.md = md;
@@ -1521,6 +1511,7 @@ static void __split_and_process_bio(struct mapped_device *md,
while (ci.sector_count && !error)
error = __split_and_process_non_flush(&ci);
}
+ dm_offload_end(&ci);
/* drop the extra reference count */
dec_pending(ci.io, error);
@@ -2248,6 +2239,16 @@ static void dm_wq_work(struct work_struct *work)
int srcu_idx;
struct dm_table *map;
+ if (!bio_list_empty(&md->rescued)) {
+ struct bio_list list;
+ spin_lock_irq(&md->deferred_lock);
+ list = md->deferred;
+ bio_list_init(&md->deferred);
+ spin_unlock_irq(&md->deferred_lock);
+ while ((c = bio_list_pop(&md->deferred)) != NULL)
+ generic_make_request(c);
+ }
+
map = dm_get_live_table(md, &srcu_idx);
while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) {
@@ -2796,7 +2797,7 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, enum dm_qu
BUG();
}
- pools->bs = bioset_create(pool_size, front_pad, BIOSET_NEED_RESCUER);
+ pools->bs = bioset_create(pool_size, front_pad, 0);
if (!pools->bs)
goto out;
--
2.14.0.rc0.dirty
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