mm: dmapool: add/remove sysfs file outside of the pool lock lock (01c2965f) · Commits · 戴 / test

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 existing dependency chain (in reverse order) is: | |-> #1 (pools_lock){+.+.+.}: | [<c0114ae8>] show_pools+0x30/0xf8 | [<c0313210>] dev_attr_show+0x1c/0x48 | [<c0180e84>] sysfs_kf_seq_show+0x88/0x10c | [<c017f960>] kernfs_seq_show+0x24/0x28 | [<c013efc4>] seq_read+0x1b8/0x480 | [<c011e820>] vfs_read+0x8c/0x148 | [<c011ea10>] SyS_read+0x40/0x8c | [<c000e960>] ret_fast_syscall+0x0/0x48 | |-> #0 (s_active#28){++++.+}: | [<c017e9ac>] __kernfs_remove+0x258/0x2ec | [<c017f754>] kernfs_remove_by_name_ns+0x3c/0x88 | [<c0114a7c>] dma_pool_destroy+0x148/0x17c | [<c03ad288>] hcd_buffer_destroy+0x20/0x34 | [<c03a4780>] usb_remove_hcd+0x110/0x1a4 The problem is the lock order of pools_lock and kernfs_mutex in dma_pool_destroy() vs show_pools() call path. This patch breaks out the creation of the sysfs file outside of the pools_lock mutex. The newly added pools_reg_lock ensures that there is no race of create vs destroy code path in terms whether or not the sysfs file has to be deleted (and was it deleted before we try to create a new one) and what to do if device_create_file() failed. Signed-off-by:

Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/dmapool.c

+35 −8

Original line number	Diff line number	Diff line
		@@ -62,6 +62,7 @@ struct dma_page { /* cacheable header for 'allocation' bytes */
		};

		static DEFINE_MUTEX(pools_lock);
		static DEFINE_MUTEX(pools_reg_lock);

		static ssize_t
		show_pools(struct device dev, struct device_attribute attr, char *buf)
		@@ -132,6 +133,7 @@ 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;
		@@ -172,15 +174,34 @@ struct dma_pool dma_pool_create(const char name, struct device *dev,

		INIT_LIST_HEAD(&retval->pools);

		/*
		* pools_lock ensures that the ->dma_pools list does not get corrupted.
		* pools_reg_lock ensures that there is not a race between
		* dma_pool_create() and dma_pool_destroy() or within dma_pool_create()
		* when the first invocation of dma_pool_create() failed on
		* device_create_file() and the second assumes that it has been done (I
		* know it is a short window).
		*/
		mutex_lock(&pools_reg_lock);
		mutex_lock(&pools_lock);
		if (list_empty(&dev->dma_pools) &&
		device_create_file(dev, &dev_attr_pools)) {
		kfree(retval);
		retval = NULL;
		} else
		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);
		mutex_unlock(&pools_reg_lock);
		kfree(retval);
		return NULL;
		}
		}
		mutex_unlock(&pools_reg_lock);
		return retval;
		}
		EXPORT_SYMBOL(dma_pool_create);
		@@ -251,11 +272,17 @@ 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_reg_lock);
		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);
		mutex_unlock(&pools_reg_lock);

		while (!list_empty(&pool->page_list)) {
		struct dma_page *page;

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