Commit 025b9685 authored by Joe Thornber's avatar Joe Thornber Committed by Alasdair G Kergon
Browse files

dm thin: remove cells from stack 



This patch takes advantage of the new bio-prison interface where the
memory is now passed in rather than using a mempool in bio-prison.
This allows the map function to avoid performing potentially-blocking
allocations that could lead to deadlocks: We want to avoid the cell
allocation that is done in bio_detain.

(The potential for mempool deadlocks still remains in other functions
that use bio_detain.)

Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 6beca5eb

drivers/md/dm-bio-prison.c

+0 −7
Original line number Diff line number Diff line
@@ -14,13 +14,6 @@ 


/*----------------------------------------------------------------*/



struct dm_bio_prison_cell {

	struct hlist_node list;

	struct dm_cell_key key;

	struct bio *holder;

	struct bio_list bios;

};



struct dm_bio_prison {

	spinlock_t lock;

	mempool_t *cell_pool;

drivers/md/dm-bio-prison.h

+11 −1
Original line number Diff line number Diff line
@@ -22,7 +22,6 @@ 
 * subsequently unlocked the bios become available.

 */

struct dm_bio_prison;

struct dm_bio_prison_cell;



/* FIXME: this needs to be more abstract */

struct dm_cell_key {
@@ -31,6 +30,17 @@ struct dm_cell_key { 
	dm_block_t block;

};



/*

 * Treat this as opaque, only in header so callers can manage allocation

 * themselves.

 */

struct dm_bio_prison_cell {

	struct hlist_node list;

	struct dm_cell_key key;

	struct bio *holder;

	struct bio_list bios;

};



struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells);

void dm_bio_prison_destroy(struct dm_bio_prison *prison);

drivers/md/dm-thin.c

+32 −15
Original line number Diff line number Diff line
@@ -229,6 +229,17 @@ struct thin_c { 


/*----------------------------------------------------------------*/



/*

 * wake_worker() is used when new work is queued and when pool_resume is

 * ready to continue deferred IO processing.

 */

static void wake_worker(struct pool *pool)

{

	queue_work(pool->wq, &pool->worker);

}



/*----------------------------------------------------------------*/



static int bio_detain(struct pool *pool, struct dm_cell_key *key, struct bio *bio,

		      struct dm_bio_prison_cell **cell_result)

{
@@ -268,6 +279,19 @@ static void cell_release_no_holder(struct pool *pool, 
	dm_bio_prison_free_cell(pool->prison, cell);

}



static void cell_defer_no_holder_no_free(struct thin_c *tc,

					 struct dm_bio_prison_cell *cell)

{

	struct pool *pool = tc->pool;

	unsigned long flags;



	spin_lock_irqsave(&pool->lock, flags);

	dm_cell_release_no_holder(pool->prison, cell, &pool->deferred_bios);

	spin_unlock_irqrestore(&pool->lock, flags);



	wake_worker(pool);

}



static void cell_error(struct pool *pool,

		       struct dm_bio_prison_cell *cell)

{
@@ -477,15 +501,6 @@ static void remap_and_issue(struct thin_c *tc, struct bio *bio, 
	issue(tc, bio);

}



/*

 * wake_worker() is used when new work is queued and when pool_resume is

 * ready to continue deferred IO processing.

 */

static void wake_worker(struct pool *pool)

{

	queue_work(pool->wq, &pool->worker);

}



/*----------------------------------------------------------------*/



/*
@@ -601,6 +616,7 @@ static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m) 
	list_del(&m->list);

	mempool_free(m, m->tc->pool->mapping_pool);

}



static void process_prepared_mapping(struct dm_thin_new_mapping *m)

{

	struct thin_c *tc = m->tc;
@@ -1438,7 +1454,8 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio) 
	dm_block_t block = get_bio_block(tc, bio);

	struct dm_thin_device *td = tc->td;

	struct dm_thin_lookup_result result;

	struct dm_bio_prison_cell *cell1, *cell2;

	struct dm_bio_prison_cell cell1, cell2;

	struct dm_bio_prison_cell *cell_result;

	struct dm_cell_key key;



	thin_hook_bio(tc, bio);
@@ -1480,18 +1497,18 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio) 
		}



		build_virtual_key(tc->td, block, &key);

		if (bio_detain(tc->pool, &key, bio, &cell1))

		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))

			return DM_MAPIO_SUBMITTED;



		build_data_key(tc->td, result.block, &key);

		if (bio_detain(tc->pool, &key, bio, &cell2)) {

			cell_defer_no_holder(tc, cell1);

		if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2, &cell_result)) {

			cell_defer_no_holder_no_free(tc, &cell1);

			return DM_MAPIO_SUBMITTED;

		}



		inc_all_io_entry(tc->pool, bio);

		cell_defer_no_holder(tc, cell2);

		cell_defer_no_holder(tc, cell1);

		cell_defer_no_holder_no_free(tc, &cell2);

		cell_defer_no_holder_no_free(tc, &cell1);



		remap(tc, bio, result.block);

		return DM_MAPIO_REMAPPED;

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