Re: [PATCH 2/2] ocfs2: fix deadlocks when taking inode lock at vfs entry points

From: Eric Ren
Date: Sun Jan 15 2017 - 22:20:32 EST


On 01/16/2017 11:13 AM, Junxiao Bi wrote:
On 01/16/2017 11:06 AM, Eric Ren wrote:
Hi Junxiao,

On 01/16/2017 10:46 AM, Junxiao Bi wrote:
If had_lock==true, it is a bug? I think we should BUG_ON for it, that
can help us catch bug at the first time.
Good idea! But I'm not sure if "ocfs2_setattr" is always the first one
who takes the cluster lock.
It's harder for me to name all the possible paths;-/
The BUG_ON() can help catch the path where ocfs2_setattr is not the
first one.
Yes, I understand. But, the problem is that the vfs entries calling
order is out of our control.
I don't want to place an assertion where I'm not 100% sure it's
absolutely right;-)
If it is not the first one, is it another recursive locking bug? In this
case, if you don't like BUG_ON(), you can dump the call trace and print
some warning message.

Yes! I like this idea, will add it in next version, thanks!

Eric


Thanks,
Junxiao.
Thanks,
Eric

Thanks,
Junxiao.

+ if (had_lock)
+ arg_flags = OCFS2_META_LOCK_GETBH;
+ status = ocfs2_inode_lock_full(inode, &bh, 1, arg_flags);
if (status < 0) {
if (status != -ENOENT)
mlog_errno(status);
goto bail_unlock_rw;
}
- inode_locked = 1;
+ if (!had_lock) {
+ ocfs2_add_holder(lockres, &oh);
+ inode_locked = 1;
+ }
if (size_change) {
status = inode_newsize_ok(inode, attr->ia_size);
@@ -1260,7 +1270,8 @@ int ocfs2_setattr(struct dentry *dentry, struct
iattr *attr)
bail_commit:
ocfs2_commit_trans(osb, handle);
bail_unlock:
- if (status) {
+ if (status && inode_locked) {
+ ocfs2_remove_holder(lockres, &oh);
ocfs2_inode_unlock(inode, 1);
inode_locked = 0;
}
@@ -1278,8 +1289,10 @@ int ocfs2_setattr(struct dentry *dentry,
struct iattr *attr)
if (status < 0)
mlog_errno(status);
}
- if (inode_locked)
+ if (inode_locked) {
+ ocfs2_remove_holder(lockres, &oh);
ocfs2_inode_unlock(inode, 1);
+ }
brelse(bh);
return status;
@@ -1321,20 +1334,31 @@ int ocfs2_getattr(struct vfsmount *mnt,
int ocfs2_permission(struct inode *inode, int mask)
{
int ret;
+ int has_locked;
+ struct ocfs2_holder oh;
+ struct ocfs2_lock_res *lockres;
if (mask & MAY_NOT_BLOCK)
return -ECHILD;
- ret = ocfs2_inode_lock(inode, NULL, 0);
- if (ret) {
- if (ret != -ENOENT)
- mlog_errno(ret);
- goto out;
+ lockres = &OCFS2_I(inode)->ip_inode_lockres;
+ has_locked = (ocfs2_is_locked_by_me(lockres) != NULL);
The same thing as ocfs2_setattr.
OK. I will think over your suggestions!

Thanks,
Eric

Thanks,
Junxiao.
+ if (!has_locked) {
+ ret = ocfs2_inode_lock(inode, NULL, 0);
+ if (ret) {
+ if (ret != -ENOENT)
+ mlog_errno(ret);
+ goto out;
+ }
+ ocfs2_add_holder(lockres, &oh);
}
ret = generic_permission(inode, mask);
- ocfs2_inode_unlock(inode, 0);
+ if (!has_locked) {
+ ocfs2_remove_holder(lockres, &oh);
+ ocfs2_inode_unlock(inode, 0);
+ }
out:
return ret;
}