Re: hundreds of mount --bind mountpoints?

Trond Myklebust
2001-04-24T22:00:23Z

>>>>> " " == Alexander Viro <viro@math.psu.edu> writes:

> On Mon, 23 Apr 2001, Jan Harkes wrote:

>> On Mon, Apr 23, 2001 at 10:45:05PM +0200, Ingo Oeser wrote:

>> > BTW: Is it still less than one page? Then it doesn't make me
>> > nervous. Why? Guess what granularity we allocate at, if we
>> > just store pointers instead of the inode.u. Or do you like
>> > every FS creating his own slab cache?

> Oh, for crying out loud. All it takes is half an hour per
> filesystem. Here - completely untested patch that does it for
> NFS. Took about that long. Absolutely straightforward, very
> easy to verify correctness.

> Some stuff may need tweaking, but not much (e.g. some functions
> should take nfs_inode_info instead of inodes, etc.). From the
> look of flushd cache it seems that we would be better off with
> cyclic lists instead of single-linked ones for the hash, but I
> didn't look deep enough.

> So consider the patch below as proof-of-concept. Enjoy:

Hi Al,

I believe your patch introduces a race for the NFS case. The problem
lies in the fact that nfs_find_actor() needs to read several of the
fields from nfs_inode_info. By adding an allocation after the inode
has been hashed, you are creating a window during which the inode can
be found by find_inode(), but during which you aren't even guaranteed
that the nfs_inode_info exists let alone that it's been initialized
by nfs_fill_inode().

One solution could be to have find_inode sleep on encountering a
locked inode. It would have to be something along the lines of

static struct inode * find_inode(struct super_block * sb, unsigned long ino, struct list_head *head, find_inode_t find_actor, void *opaque)
{
struct list_head *tmp;
struct inode * inode;

tmp = head;
for (;;) {
tmp = tmp->next;
inode = NULL;
if (tmp == head)
break;
inode = list_entry(tmp, struct inode, i_hash);
if (inode->i_ino != ino)
continue;
if (inode->i_sb != sb)
continue;
if (find_actor) {
if (inode->i_state & I_LOCK) {
spin_unlock(&inode_lock);
__wait_on_inode(inode);
spin_lock(&inode_lock);
tmp = head;
continue;
}
if (!find_actor(inode, ino, opaque))
continue;
}
break;
}
return inode;
}

Cheers,
Trond