Re: [dm-devel] [PATCH 2/2] block: Avoid deadlocks with bioallocation by stacking drivers

From: Kent Overstreet
Date: Mon Sep 10 2012 - 19:01:29 EST

On Mon, Sep 10, 2012 at 11:50:57PM +0100, Alasdair G Kergon wrote:
> On Mon, Sep 10, 2012 at 03:09:10PM -0700, Tejun Heo wrote:
> > On Mon, Sep 10, 2012 at 02:56:33PM -0700, Kent Overstreet wrote:
> > > commit df7e63cbffa3065fcc4ba2b9a93418d7c7312243
> > > Author: Kent Overstreet <koverstreet@xxxxxxxxxx>
> > > Date: Mon Sep 10 14:33:46 2012 -0700
> > >
> > > block: Avoid deadlocks with bio allocation by stacking drivers
>
> > > Note that this doesn't do anything for allocation from other mempools.
>
> Note that dm has several cases of this, so this patch should not be used with
> dm yet.

That just means it won't affect dm one way or the other for those
allocations.

> Mikulas is studying those cases to see whether anything like this
> might be feasible/sensible or not.

I've got a patch that eliminates one of the per bio mempools in dm, and
I'll probably work on the rest after I finish off with immutable biovecs
- which is mostly done, just cleaning up/testing/pushing patches in now.


commit 8754349145edfc791450d3ad54c19f0f3715c86c
Author: Kent Overstreet <koverstreet@xxxxxxxxxx>
Date: Tue Sep 4 06:17:56 2012 -0700

dm: Use bioset's front_pad for dm_target_io

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index f2eb730..3cf39b0 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -71,6 +71,7 @@ struct dm_target_io {
struct dm_io *io;
struct dm_target *ti;
union map_info info;
+ struct bio clone;
};

/*
@@ -174,7 +175,7 @@ struct mapped_device {
* io objects are allocated from here.
*/
mempool_t *io_pool;
- mempool_t *tio_pool;
+ mempool_t *rq_tio_pool;

struct bio_set *bs;

@@ -214,15 +215,8 @@ struct dm_md_mempools {

#define MIN_IOS 256
static struct kmem_cache *_io_cache;
-static struct kmem_cache *_tio_cache;
static struct kmem_cache *_rq_tio_cache;

-/*
- * Unused now, and needs to be deleted. But since io_pool is overloaded and it's
- * still used for _io_cache, I'm leaving this for a later cleanup
- */
-static struct kmem_cache *_rq_bio_info_cache;
-
static int __init local_init(void)
{
int r = -ENOMEM;
@@ -232,22 +226,13 @@ static int __init local_init(void)
if (!_io_cache)
return r;

- /* allocate a slab for the target ios */
- _tio_cache = KMEM_CACHE(dm_target_io, 0);
- if (!_tio_cache)
- goto out_free_io_cache;
-
_rq_tio_cache = KMEM_CACHE(dm_rq_target_io, 0);
if (!_rq_tio_cache)
- goto out_free_tio_cache;
-
- _rq_bio_info_cache = KMEM_CACHE(dm_rq_clone_bio_info, 0);
- if (!_rq_bio_info_cache)
- goto out_free_rq_tio_cache;
+ goto out_free_io_cache;

r = dm_uevent_init();
if (r)
- goto out_free_rq_bio_info_cache;
+ goto out_free_rq_tio_cache;

_major = major;
r = register_blkdev(_major, _name);
@@ -261,12 +246,8 @@ static int __init local_init(void)

out_uevent_exit:
dm_uevent_exit();
-out_free_rq_bio_info_cache:
- kmem_cache_destroy(_rq_bio_info_cache);
out_free_rq_tio_cache:
kmem_cache_destroy(_rq_tio_cache);
-out_free_tio_cache:
- kmem_cache_destroy(_tio_cache);
out_free_io_cache:
kmem_cache_destroy(_io_cache);

@@ -275,9 +256,7 @@ out_free_io_cache:

static void local_exit(void)
{
- kmem_cache_destroy(_rq_bio_info_cache);
kmem_cache_destroy(_rq_tio_cache);
- kmem_cache_destroy(_tio_cache);
kmem_cache_destroy(_io_cache);
unregister_blkdev(_major, _name);
dm_uevent_exit();
@@ -461,20 +440,15 @@ static void free_io(struct mapped_device *md, struct dm_io *io)
mempool_free(io, md->io_pool);
}

-static void free_tio(struct mapped_device *md, struct dm_target_io *tio)
-{
- mempool_free(tio, md->tio_pool);
-}
-
static struct dm_rq_target_io *alloc_rq_tio(struct mapped_device *md,
gfp_t gfp_mask)
{
- return mempool_alloc(md->tio_pool, gfp_mask);
+ return mempool_alloc(md->rq_tio_pool, gfp_mask);
}

static void free_rq_tio(struct dm_rq_target_io *tio)
{
- mempool_free(tio, tio->md->tio_pool);
+ mempool_free(tio, tio->md->rq_tio_pool);
}

static int md_in_flight(struct mapped_device *md)
@@ -658,7 +632,6 @@ static void clone_endio(struct bio *bio, int error)
int r = 0;
struct dm_target_io *tio = bio->bi_private;
struct dm_io *io = tio->io;
- struct mapped_device *md = tio->io->md;
dm_endio_fn endio = tio->ti->type->end_io;

if (!bio_flagged(bio, BIO_UPTODATE) && !error)
@@ -681,7 +654,6 @@ static void clone_endio(struct bio *bio, int error)
}
}

- free_tio(md, tio);
bio_put(bio);
dec_pending(io, error);
}
@@ -998,13 +970,16 @@ int dm_set_target_max_io_len(struct dm_target *ti, sector_t len)
}
EXPORT_SYMBOL_GPL(dm_set_target_max_io_len);

-static void __map_bio(struct dm_target *ti, struct bio *clone,
- struct dm_target_io *tio)
+static void __map_bio(struct dm_io *io, struct dm_target *ti, struct bio *clone)
{
+ struct dm_target_io *tio = container_of(clone, struct dm_target_io, clone);
int r;
sector_t sector;
struct mapped_device *md;

+ tio->io = io;
+ tio->ti = ti;
+
clone->bi_end_io = clone_endio;
clone->bi_private = tio;

@@ -1028,7 +1003,6 @@ static void __map_bio(struct dm_target *ti, struct bio *clone,
md = tio->io->md;
dec_pending(tio->io, r);
bio_put(clone);
- free_tio(md, tio);
} else if (r) {
DMWARN("unimplemented target map return value: %d", r);
BUG();
@@ -1104,26 +1078,18 @@ static struct bio *clone_bio(struct bio *bio, sector_t sector,
return clone;
}

-static struct dm_target_io *alloc_tio(struct clone_info *ci,
- struct dm_target *ti)
+static void init_tio(struct bio *bio)
{
- struct dm_target_io *tio = mempool_alloc(ci->md->tio_pool, GFP_NOIO);
-
- tio->io = ci->io;
- tio->ti = ti;
+ struct dm_target_io *tio = container_of(bio, struct dm_target_io, clone);
memset(&tio->info, 0, sizeof(tio->info));
-
- return tio;
}

static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
unsigned request_nr, sector_t len)
{
- struct dm_target_io *tio = alloc_tio(ci, ti);
+ struct dm_target_io *tio;
struct bio *clone;

- tio->info.target_request_nr = request_nr;
-
/*
* Discard requests require the bio's inline iovecs be initialized.
* ci->bio->bi_max_vecs is BIO_INLINE_VECS anyway, for both flush
@@ -1136,7 +1102,10 @@ static void __issue_target_request(struct clone_info *ci, struct dm_target *ti,
clone->bi_size = to_bytes(len);
}

- __map_bio(ti, clone, tio);
+ tio = container_of(clone, struct dm_target_io, clone);
+ tio->info.target_request_nr = request_nr;
+
+ __map_bio(ci->io, ti, clone);
}

static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
@@ -1166,13 +1135,13 @@ static int __clone_and_map_empty_flush(struct clone_info *ci)
static void __clone_and_map_simple(struct clone_info *ci, struct dm_target *ti)
{
struct bio *clone, *bio = ci->bio;
- struct dm_target_io *tio;

- tio = alloc_tio(ci, ti);
clone = clone_bio(bio, ci->sector, ci->idx,
bio->bi_vcnt - ci->idx, ci->sector_count,
ci->md->bs);
- __map_bio(ti, clone, tio);
+
+ init_tio(clone);
+ __map_bio(ci->io, ti, clone);
ci->sector_count = 0;
}

@@ -1213,7 +1182,6 @@ static int __clone_and_map(struct clone_info *ci)
struct bio *clone, *bio = ci->bio;
struct dm_target *ti;
sector_t len = 0, max;
- struct dm_target_io *tio;

if (unlikely(bio->bi_rw & REQ_DISCARD))
return __clone_and_map_discard(ci);
@@ -1250,10 +1218,11 @@ static int __clone_and_map(struct clone_info *ci)
len += bv_len;
}

- tio = alloc_tio(ci, ti);
clone = clone_bio(bio, ci->sector, ci->idx, i - ci->idx, len,
ci->md->bs);
- __map_bio(ti, clone, tio);
+
+ init_tio(clone);
+ __map_bio(ci->io, ti, clone);

ci->sector += len;
ci->sector_count -= len;
@@ -1278,12 +1247,12 @@ static int __clone_and_map(struct clone_info *ci)

len = min(remaining, max);

- tio = alloc_tio(ci, ti);
clone = split_bvec(bio, ci->sector, ci->idx,
bv->bv_offset + offset, len,
ci->md->bs);

- __map_bio(ti, clone, tio);
+ init_tio(clone);
+ __map_bio(ci->io, ti, clone);

ci->sector += len;
ci->sector_count -= len;
@@ -1911,8 +1880,8 @@ static void free_dev(struct mapped_device *md)
unlock_fs(md);
bdput(md->bdev);
destroy_workqueue(md->wq);
- if (md->tio_pool)
- mempool_destroy(md->tio_pool);
+ if (md->rq_tio_pool)
+ mempool_destroy(md->rq_tio_pool);
if (md->io_pool)
mempool_destroy(md->io_pool);
if (md->bs)
@@ -1935,16 +1904,16 @@ static void __bind_mempools(struct mapped_device *md, struct dm_table *t)
{
struct dm_md_mempools *p;

- if (md->io_pool && md->tio_pool && md->bs)
+ if ((md->io_pool || md->rq_tio_pool) && md->bs)
/* the md already has necessary mempools */
goto out;

p = dm_table_get_md_mempools(t);
- BUG_ON(!p || md->io_pool || md->tio_pool || md->bs);
+ BUG_ON(!p || md->io_pool || md->rq_tio_pool || md->bs);

md->io_pool = p->io_pool;
p->io_pool = NULL;
- md->tio_pool = p->tio_pool;
+ md->rq_tio_pool = p->tio_pool;
p->tio_pool = NULL;
md->bs = p->bs;
p->bs = NULL;
@@ -2693,40 +2662,29 @@ struct dm_md_mempools *dm_alloc_md_mempools(unsigned type, unsigned integrity)
if (!pools)
return NULL;

- pools->io_pool = (type == DM_TYPE_BIO_BASED) ?
- mempool_create_slab_pool(MIN_IOS, _io_cache) :
- mempool_create_slab_pool(MIN_IOS, _rq_bio_info_cache);
+ if (type == DM_TYPE_BIO_BASED)
+ pools->io_pool = mempool_create_slab_pool(MIN_IOS, _io_cache);
if (!pools->io_pool)
- goto free_pools_and_out;
+ goto err;

- pools->tio_pool = (type == DM_TYPE_BIO_BASED) ?
- mempool_create_slab_pool(MIN_IOS, _tio_cache) :
- mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
+ if (type == DM_TYPE_REQUEST_BASED)
+ pools->tio_pool =
+ mempool_create_slab_pool(MIN_IOS, _rq_tio_cache);
if (!pools->tio_pool)
- goto free_io_pool_and_out;
+ goto err;

pools->bs = bioset_create(pool_size,
- offsetof(struct dm_rq_clone_bio_info, clone));
+ max(offsetof(struct dm_target_io, clone),
+ offsetof(struct dm_rq_clone_bio_info, clone)));
if (!pools->bs)
- goto free_tio_pool_and_out;
+ goto err;

if (integrity && bioset_integrity_create(pools->bs, pool_size))
- goto free_bioset_and_out;
+ goto err;

return pools;
-
-free_bioset_and_out:
- bioset_free(pools->bs);
-
-free_tio_pool_and_out:
- mempool_destroy(pools->tio_pool);
-
-free_io_pool_and_out:
- mempool_destroy(pools->io_pool);
-
-free_pools_and_out:
- kfree(pools);
-
+err:
+ dm_free_md_mempools(pools);
return NULL;
}

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