fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode()

fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode()

If generic_drop_inode() returns true, it means iput_final() can evict
this inode regardless of whether it is dirty or not. If we check
I_DONTCACHE in generic_drop_inode(), any inode with this bit set will be
evicted unconditionally. This is not the desired behavior because
I_DONTCACHE only means the inode shouldn't be cached on the LRU list.
As for whether we need to evict this inode, this is what
generic_drop_inode() should do. This patch corrects the usage of
I_DONTCACHE.

This patch was proposed in [1].

[1]: https://lore.kernel.org/linux-fsdevel/20200831003407[email protected]/

Fixes: dae2f8ed7992 ("fs: Lift XFS_IDONTCACHE to the VFS layer")
Signed-off-by: Hao Li <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Signed-off-by: Al Viro <[email protected]>