[PATCH] mm: dmapool: add/remove sysfs file outside of the pool lock

[Sebastian Andrzej Siewior]

cat /sys/…/pools followed by removal the device leads to:

|======================================================
|[ INFO: possible circular locking dependency detected ]
|3.17.0-rc4+ #1498 Not tainted
|-------------------------------------------------------
|rmmod/2505 is trying to acquire lock:
| (s_active#28){++++.+}, at: [<c017f754>] kernfs_remove_by_name_ns+0x3c/0x88
|
|but task is already holding lock:
| (pools_lock){+.+.+.}, at: [<c011494c>] dma_pool_destroy+0x18/0x17c
|
|which lock already depends on the new lock.

The problem is the lock order of pools_lock and kernfs_mutex in
dma_pool_destroy() vs show_pools().

This patch breaks out the creation of the sysfs file outside of the
pools_lock mutex.
In theory we would have to create the link in the error path of
device_create_file() in case the dev->dma_pools list is not empty. In
reality I doubt that there will be a single device creating dma-pools in
parallel where it would matter.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
 mm/dmapool.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 306baa594f95..0cad8ee7891f 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -132,6 +132,7 @@ struct dma_pool *dma_pool_create(const char *name, struct 
device *dev,
 {
        struct dma_pool *retval;
        size_t allocation;
+       bool empty = false;
 
        if (align == 0) {
                align = 1;
@@ -173,14 +174,22 @@ struct dma_pool *dma_pool_create(const char *name, struct 
device *dev,
        INIT_LIST_HEAD(&retval->pools);
 
        mutex_lock(&pools_lock);
-       if (list_empty(&dev->dma_pools) &&
-           device_create_file(dev, &dev_attr_pools)) {
-               kfree(retval);
-               return NULL;
-       } else
-               list_add(&retval->pools, &dev->dma_pools);
+       if (list_empty(&dev->dma_pools))
+               empty = true;
+       list_add(&retval->pools, &dev->dma_pools);
        mutex_unlock(&pools_lock);
-
+       if (empty) {
+               int err;
+
+               err = device_create_file(dev, &dev_attr_pools);
+               if (err) {
+                       mutex_lock(&pools_lock);
+                       list_del(&retval->pools);
+                       mutex_unlock(&pools_lock);
+                       kfree(retval);
+                       return NULL;
+               }
+       }
        return retval;
 }
 EXPORT_SYMBOL(dma_pool_create);
@@ -251,11 +260,15 @@ static void pool_free_page(struct dma_pool *pool, struct 
dma_page *page)
  */
 void dma_pool_destroy(struct dma_pool *pool)
 {
+       bool empty = false;
+
        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);
+               empty = true;
        mutex_unlock(&pools_lock);
+       if (empty)
+               device_remove_file(pool->dev, &dev_attr_pools);
 
        while (!list_empty(&pool->page_list)) {
                struct dma_page *page;
-- 
2.1.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/