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trelay: fix deadlock on remove

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Upon writing to "remove" file, debugfs_remove_recursive() blocks while
holding rtnl_lock. This is because debugfs' file_ops callbacks are
executed in debugfs_use_file_*() context which prevents file removal.

Fix this by only flagging the device for removal and then do the cleanup
in file_ops.release callback which is executed out of that context.

Signed-off-by: Ali MJ Al-Nasrawy <alimjalnasrawy@gmail.com>
This commit is contained in:
Ali MJ Al-Nasrawy 2019-09-25 17:47:12 +03:00 committed by Hauke Mehrtens
parent 77cfc0739d
commit c2635b871d
1 changed files with 23 additions and 9 deletions
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32
package/kernel/trelay/src/trelay.c
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@ -27,6 +27,7 @@ struct trelay {
struct list_head list;
struct net_device *dev1, *dev2;
struct dentry *debugfs;
int to_remove;
char name[];
};
@ -60,13 +61,16 @@ static int trelay_do_remove(struct trelay *tr)
{
list_del(&tr->list);
/* First and before all, ensure that the debugfs file is removed
* to prevent dangling pointer in file->private_data */
debugfs_remove_recursive(tr->debugfs);
dev_put(tr->dev1);
dev_put(tr->dev2);
netdev_rx_handler_unregister(tr->dev1);
netdev_rx_handler_unregister(tr->dev2);
debugfs_remove_recursive(tr->debugfs);
kfree(tr);
return 0;
@ -106,23 +110,33 @@ static ssize_t trelay_remove_write(struct file *file, const char __user *ubuf,
size_t count, loff_t *ppos)
{
struct trelay *tr = file->private_data;
int ret;
rtnl_lock();
ret = trelay_do_remove(tr);
rtnl_unlock();
if (ret < 0)
return ret;
tr->to_remove = 1;
return count;
}
static int trelay_remove_release(struct inode *inode, struct file *file)
{
struct trelay *tr, *tmp;
/* This is the only file op that is called outside debugfs_use_file_*()
* context which means that: (1) this file can be removed and
* (2) file->private_data may no longer be valid */
rtnl_lock();
list_for_each_entry_safe(tr, tmp, &trelay_devs, list)
if (tr->to_remove)
trelay_do_remove(tr);
rtnl_unlock();
return 0;
}
static const struct file_operations fops_remove = {
.owner = THIS_MODULE,
.open = trelay_open,
.write = trelay_remove_write,
.llseek = default_llseek,
.release = trelay_remove_release,
};