[lustre-devel] [PATCH v2] lustre: mdc: fix possible deadlock in chlg_open()
NeilBrown
neilb at suse.com
Wed Oct 31 16:01:33 PDT 2018
Lockdep reports a possible deadlock between chlg_open() and
mdc_changelog_cdev_init()
mdc_changelog_cdev_init() takes chlg_registered_dev_lock and then
calls misc_register() which takes misc_mtx.
chlg_open() is called while misc_mtx is held, and tries to take
chlg_registered_dev_lock.
If these two functions race, a deadlock can occur as each thread will
hold one of the locks while trying to take the other.
chlg_open() does not need to take a lock. It only uses the
lock to stablize a list while looking for the matching
chlg_registered_dev, and this can be found directly by examining
file->private_data.
So remove chlg_obd_get(), and use file->private_data to find the
obd_device.
Also ensure the device is fully initialized before calling
misc_register(). This means setting up some list linkage before the
call, and tearing it down if there is an error.
Signed-off-by: NeilBrown <neilb at suse.com>
---
This is the revised version with the problem identified by Quentin
fixed.
drivers/staging/lustre/lustre/mdc/mdc_changelog.c | 46 +++++++----------------
1 file changed, 14 insertions(+), 32 deletions(-)
diff --git a/drivers/staging/lustre/lustre/mdc/mdc_changelog.c b/drivers/staging/lustre/lustre/mdc/mdc_changelog.c
index d83507cbf95c..af29ea73c48a 100644
--- a/drivers/staging/lustre/lustre/mdc/mdc_changelog.c
+++ b/drivers/staging/lustre/lustre/mdc/mdc_changelog.c
@@ -444,31 +444,6 @@ static ssize_t chlg_write(struct file *file, const char __user *buff,
return rc < 0 ? rc : count;
}
-/**
- * Find the OBD device associated to a changelog character device.
- * @param[in] cdev character device instance descriptor
- * @return corresponding OBD device or NULL if none was found.
- */
-static struct obd_device *chlg_obd_get(dev_t cdev)
-{
- int minor = MINOR(cdev);
- struct obd_device *obd = NULL;
- struct chlg_registered_dev *curr;
-
- mutex_lock(&chlg_registered_dev_lock);
- list_for_each_entry(curr, &chlg_registered_devices, ced_link) {
- if (curr->ced_misc.minor == minor) {
- /* take the first available OBD device attached */
- obd = list_first_entry(&curr->ced_obds,
- struct obd_device,
- u.cli.cl_chg_dev_linkage);
- break;
- }
- }
- mutex_unlock(&chlg_registered_dev_lock);
- return obd;
-}
-
/**
* Open handler, initialize internal CRS state and spawn prefetch thread if
* needed.
@@ -479,12 +454,16 @@ static struct obd_device *chlg_obd_get(dev_t cdev)
static int chlg_open(struct inode *inode, struct file *file)
{
struct chlg_reader_state *crs;
- struct obd_device *obd = chlg_obd_get(inode->i_rdev);
+ struct miscdevice *misc = file->private_data;
+ struct chlg_registered_dev *dev;
+ struct obd_device *obd;
struct task_struct *task;
int rc;
- if (!obd)
- return -ENODEV;
+ dev = container_of(misc, struct chlg_registered_dev, ced_misc);
+ obd = list_first_entry(&dev->ced_obds,
+ struct obd_device,
+ u.cli.cl_chg_dev_linkage);
crs = kzalloc(sizeof(*crs), GFP_KERNEL);
if (!crs)
@@ -669,13 +648,16 @@ int mdc_changelog_cdev_init(struct obd_device *obd)
goto out_unlock;
}
+ list_add_tail(&obd->u.cli.cl_chg_dev_linkage, &entry->ced_obds);
+ list_add_tail(&entry->ced_link, &chlg_registered_devices);
+
/* Register new character device */
rc = misc_register(&entry->ced_misc);
- if (rc != 0)
+ if (rc != 0) {
+ list_del_init(&obd->u.cli.cl_chg_dev_linkage);
+ list_del(&entry->ced_link);
goto out_unlock;
-
- list_add_tail(&obd->u.cli.cl_chg_dev_linkage, &entry->ced_obds);
- list_add_tail(&entry->ced_link, &chlg_registered_devices);
+ }
entry = NULL; /* prevent it from being freed below */
--
2.14.0.rc0.dirty
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