Re: [PATCH v2 bpf-next 2/4] bpf: Make bpf inode storage available to tracing program

From: Martin KaFai Lau
Date: Tue Nov 12 2024 - 18:01:10 EST


On 11/12/24 12:36 AM, Song Liu wrote:
void __destroy_inode(struct inode *inode)
{
BUG_ON(inode_has_buffers(inode));
+ bpf_inode_storage_free(inode);

Not sure if this is done in the rcu callback (i.e. after the rcu gp). Please check.

inode_detach_wb(inode);
security_inode_free(inode);
fsnotify_inode_delete(inode);

[ ... ]

@@ -136,12 +119,7 @@ BPF_CALL_5(bpf_inode_storage_get, struct bpf_map *, map, struct inode *, inode,
if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
return (unsigned long)NULL;
- /* explicitly check that the inode_storage_ptr is not
- * NULL as inode_storage_lookup returns NULL in this case and
- * bpf_local_storage_update expects the owner to have a
- * valid storage pointer.
- */
- if (!inode || !inode_storage_ptr(inode))
+ if (!inode)
return (unsigned long)NULL;

There is an atomic_read in this function:

/* only allocate new storage, when the inode is refcounted */
if (atomic_read(&inode->i_count) &&
flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {

If the bpf_inode_storage_free is not done after rcu gp, this will need a inc_not_zero like how the sk storage does. I think moving the storage_free to the inode rcu call back may be easier if it is not the case now.