On Fri, Jul 12, 2024 at 02:27:20PM +0800, Zhihao Cheng wrote:
> Problem description
> ===================
>
> The inode reclaiming process(See function prune_icache_sb) collects all
> reclaimable inodes and mark them with I_FREEING flag at first, at that
> time, other processes will be stuck if they try getting these inodes(See
> function find_inode_fast), then the reclaiming process destroy the
> inodes by function dispose_list().
> Some filesystems(eg. ext4 with ea_inode feature, ubifs with xattr) may
> do inode lookup in the inode evicting callback function, if the inode
> lookup is operated under the inode lru traversing context, deadlock
> problems may happen.
>
> Case 1: In function ext4_evict_inode(), the ea inode lookup could happen
> if ea_inode feature is enabled, the lookup process will be stuck under
> the evicting context like this:
>
> 1. File A has inode i_reg and an ea inode i_ea
> 2. getfattr(A, xattr_buf) // i_ea is added into lru // lru->i_ea
> 3. Then, following three processes running like this:
>
> PA PB
> echo 2 > /proc/sys/vm/drop_caches
> shrink_slab
> prune_dcache_sb
> // i_reg is added into lru, lru->i_ea->i_reg
> prune_icache_sb
> list_lru_walk_one
> inode_lru_isolate
> i_ea->i_state |= I_FREEING // set inode state
> i_ea->i_state |= I_FREEING // set inode state
Um, I don't see how this can happen. If the ea_inode is in use,
i_count will be greater than zero, and hence the inode will never be
go down the rest of the path in inode_lru_inode():
if (atomic_read(&inode->i_count) ||
...) {
list_lru_isolate(lru, &inode->i_lru);
spin_unlock(&inode->i_lock);
this_cpu_dec(nr_unused);
return LRU_REMOVED;
}
Do you have an actual reproduer which triggers this? Or would this
happen be any chance something that was dreamed up with DEPT?
- Ted
