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Subject[PATCH] mm/dmapool.c: Do not create/destroy sysfs file while holding pools_lock
From: Shaun Ruffell <sruffell@digium.com>

Eliminates a circular lock dependency reported by lockdep. When reading the
"pools" file from a PCI device via sysfs, the s_active lock is acquired before
the pools_lock. When unloading the driver and destroying the pool, pools_lock
is acquired before the s_active lock.

cat/12016 is trying to acquire lock:
(pools_lock){+.+.+.}, at: [<c04ef113>] show_pools+0x43/0x140

but task is already holding lock:
(s_active#82){++++.+}, at: [<c0554e1b>] sysfs_read_file+0xab/0x160

which lock already depends on the new lock.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
---
mm/dmapool.c | 34 ++++++++++++++++++++++++----------
1 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 03bf3bb..d693872 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -174,21 +174,28 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
init_waitqueue_head(&retval->waitq);

if (dev) {
- int ret;
+ int first_pool;

mutex_lock(&pools_lock);
if (list_empty(&dev->dma_pools))
- ret = device_create_file(dev, &dev_attr_pools);
+ first_pool = 1;
else
- ret = 0;
+ first_pool = 0;
/* note: not currently insisting "name" be unique */
- if (!ret)
- list_add(&retval->pools, &dev->dma_pools);
- else {
- kfree(retval);
- retval = NULL;
- }
+ list_add(&retval->pools, &dev->dma_pools);
mutex_unlock(&pools_lock);
+
+ if (first_pool) {
+ int ret;
+ ret = device_create_file(dev, &dev_attr_pools);
+ if (ret) {
+ mutex_lock(&pools_lock);
+ list_del(&retval->pools);
+ mutex_unlock(&pools_lock);
+ kfree(retval);
+ retval = NULL;
+ }
+ }
} else
INIT_LIST_HEAD(&retval->pools);

@@ -263,12 +270,19 @@ static void pool_free_page(struct dma_pool *pool, struct dma_page *page)
*/
void dma_pool_destroy(struct dma_pool *pool)
{
+ int last_pool;
+
mutex_lock(&pools_lock);
list_del(&pool->pools);
if (pool->dev && list_empty(&pool->dev->dma_pools))
- device_remove_file(pool->dev, &dev_attr_pools);
+ last_pool = 1;
+ else
+ last_pool = 0;
mutex_unlock(&pools_lock);

+ if (last_pool)
+ device_remove_file(pool->dev, &dev_attr_pools);
+
while (!list_empty(&pool->page_list)) {
struct dma_page *page;
page = list_entry(pool->page_list.next,
--
1.7.2.1


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