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authorDan Williams <dan.j.williams@intel.com>2017-04-30 06:57:01 -0700
committerDan Williams <dan.j.williams@intel.com>2017-05-01 13:14:37 -0700
commit565851c972b50612f3a4542e26879ffb3e906fc2 (patch)
tree88c724ad5e0a8fc3fc4c6c4479cc2f4e31377f9c /drivers/dax
parenta3e9af95f794d000debc2a5ba3186ba85a6e115f (diff)
downloadlinux-565851c972b50612f3a4542e26879ffb3e906fc2.tar.bz2
device-dax: fix sysfs attribute deadlock
Usage of device_lock() for dax_region attributes is unnecessary and deadlock prone. It's unnecessary because the order of registration / un-registration guarantees that drvdata is always valid. It's deadlock prone because it sets up this situation: ndctl D 0 2170 2082 0x00000000 Call Trace: __schedule+0x31f/0x980 schedule+0x3d/0x90 schedule_preempt_disabled+0x15/0x20 __mutex_lock+0x402/0x980 ? __mutex_lock+0x158/0x980 ? align_show+0x2b/0x80 [dax] ? kernfs_seq_start+0x2f/0x90 mutex_lock_nested+0x1b/0x20 align_show+0x2b/0x80 [dax] dev_attr_show+0x20/0x50 ndctl D 0 2186 2079 0x00000000 Call Trace: __schedule+0x31f/0x980 schedule+0x3d/0x90 __kernfs_remove+0x1f6/0x340 ? kernfs_remove_by_name_ns+0x45/0xa0 ? remove_wait_queue+0x70/0x70 kernfs_remove_by_name_ns+0x45/0xa0 remove_files.isra.1+0x35/0x70 sysfs_remove_group+0x44/0x90 sysfs_remove_groups+0x2e/0x50 dax_region_unregister+0x25/0x40 [dax] devm_action_release+0xf/0x20 release_nodes+0x16d/0x2b0 devres_release_all+0x3c/0x60 device_release_driver_internal+0x17d/0x220 device_release_driver+0x12/0x20 unbind_store+0x112/0x160 ndctl/2170 is trying to acquire the device_lock() to read an attribute, and ndctl/2186 is holding the device_lock() while trying to drain all active attribute readers. Thanks to Yi Zhang for the reproduction script. Fixes: d7fe1a67f658 ("dax: add region 'id', 'size', and 'align' attributes") Cc: <stable@vger.kernel.org> Reported-by: Yi Zhang <yizhan@redhat.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'drivers/dax')
-rw-r--r--drivers/dax/dax.c40
1 files changed, 12 insertions, 28 deletions
diff --git a/drivers/dax/dax.c b/drivers/dax/dax.c
index ef93aa84622b..5e8302d3a89c 100644
--- a/drivers/dax/dax.c
+++ b/drivers/dax/dax.c
@@ -36,36 +36,27 @@ static struct kmem_cache *dax_cache __read_mostly;
static struct super_block *dax_superblock __read_mostly;
MODULE_PARM_DESC(nr_dax, "max number of device-dax instances");
+/*
+ * Rely on the fact that drvdata is set before the attributes are
+ * registered, and that the attributes are unregistered before drvdata
+ * is cleared to assume that drvdata is always valid.
+ */
static ssize_t id_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- struct dax_region *dax_region;
- ssize_t rc = -ENXIO;
+ struct dax_region *dax_region = dev_get_drvdata(dev);
- device_lock(dev);
- dax_region = dev_get_drvdata(dev);
- if (dax_region)
- rc = sprintf(buf, "%d\n", dax_region->id);
- device_unlock(dev);
-
- return rc;
+ return sprintf(buf, "%d\n", dax_region->id);
}
static DEVICE_ATTR_RO(id);
static ssize_t region_size_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- struct dax_region *dax_region;
- ssize_t rc = -ENXIO;
+ struct dax_region *dax_region = dev_get_drvdata(dev);
- device_lock(dev);
- dax_region = dev_get_drvdata(dev);
- if (dax_region)
- rc = sprintf(buf, "%llu\n", (unsigned long long)
- resource_size(&dax_region->res));
- device_unlock(dev);
-
- return rc;
+ return sprintf(buf, "%llu\n", (unsigned long long)
+ resource_size(&dax_region->res));
}
static struct device_attribute dev_attr_region_size = __ATTR(size, 0444,
region_size_show, NULL);
@@ -73,16 +64,9 @@ static struct device_attribute dev_attr_region_size = __ATTR(size, 0444,
static ssize_t align_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
- struct dax_region *dax_region;
- ssize_t rc = -ENXIO;
+ struct dax_region *dax_region = dev_get_drvdata(dev);
- device_lock(dev);
- dax_region = dev_get_drvdata(dev);
- if (dax_region)
- rc = sprintf(buf, "%u\n", dax_region->align);
- device_unlock(dev);
-
- return rc;
+ return sprintf(buf, "%u\n", dax_region->align);
}
static DEVICE_ATTR_RO(align);