[PATCH] fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode()

[Hao Li <lihao2018.fnst@cn.fujitsu.com>]

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.GE12096@dread.disaster.area/

Fixes: dae2f8ed7992 ("fs: Lift XFS_IDONTCACHE to the VFS layer")
Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
---
This patch may have been forgotten.
Original patch: https://lore.kernel.org/linux-fsdevel/20200904075939.176366-1-lihao2018.fnst@cn.fujitsu.com/

 fs/inode.c         | 4 +++-
 include/linux/fs.h | 3 +--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 9d78c37b00b8..5eea9912a0b9 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1627,7 +1627,9 @@ static void iput_final(struct inode *inode)
 	else
 		drop = generic_drop_inode(inode);
 
-	if (!drop && (sb->s_flags & SB_ACTIVE)) {
+	if (!drop &&
+	    !(inode->i_state & I_DONTCACHE) &&
+	    (sb->s_flags & SB_ACTIVE)) {
 		inode_add_lru(inode);
 		spin_unlock(&inode->i_lock);
 		return;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8667d0cdc71e..8bde32cf9711 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2878,8 +2878,7 @@ extern int inode_needs_sync(struct inode *inode);
 extern int generic_delete_inode(struct inode *inode);
 static inline int generic_drop_inode(struct inode *inode)
 {
-	return !inode->i_nlink || inode_unhashed(inode) ||
-		(inode->i_state & I_DONTCACHE);
+	return !inode->i_nlink || inode_unhashed(inode);
 }
 extern void d_mark_dontcache(struct inode *inode);
 
-- 
2.28.0