Re: [PATCH 03/10] ext4: Remove EA inode entry from mbcache on inode eviction

Jan Kara
2022-06-16T17:30:53Z

On Thu 16-06-22 20:31:18, Ritesh Harjani wrote:
> On 22/06/14 06:05PM, Jan Kara wrote:
> > Currently we remove EA inode from mbcache as soon as its xattr refcount
> > drops to zero. However there can be pending attempts to reuse the inode
> > and thus refcount handling code has to handle the situation when
> > refcount increases from zero anyway. So save some work and just keep EA
> > inode in mbcache until it is getting evicted. At that moment we are sure
> > following iget() of EA inode will fail anyway (or wait for eviction to
> > finish and load things from the disk again) and so removing mbcache
> > entry at that moment is fine and simplifies the code a bit.
> >
> > CC: stable@vger.kernel.org
> > Fixes: 82939d7999df ("ext4: convert to mbcache2")
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> > fs/ext4/inode.c | 2 ++
> > fs/ext4/xattr.c | 24 ++++++++----------------
> > fs/ext4/xattr.h | 1 +
> > 3 files changed, 11 insertions(+), 16 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 3dce7d058985..7450ee734262 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -177,6 +177,8 @@ void ext4_evict_inode(struct inode *inode)
> >
> > trace_ext4_evict_inode(inode);
> >
> > + if (EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)
> > + ext4_evict_ea_inode(inode);
> > if (inode->i_nlink) {
> > /*
> > * When journalling data dirty buffers are tracked only in the
> > diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> > index 042325349098..7fc40fb1e6b3 100644
> > --- a/fs/ext4/xattr.c
> > +++ b/fs/ext4/xattr.c
> > @@ -436,6 +436,14 @@ static int ext4_xattr_inode_iget(struct inode *parent, unsigned long ea_ino,
> > return err;
> > }
> >
> > +/* Remove entry from mbcache when EA inode is getting evicted */
> > +void ext4_evict_ea_inode(struct inode *inode)
> > +{
> > + if (EA_INODE_CACHE(inode))
> > + mb_cache_entry_delete(EA_INODE_CACHE(inode),
> > + ext4_xattr_inode_get_hash(inode), inode->i_ino);
> > +}
> > +
> > static int
> > ext4_xattr_inode_verify_hashes(struct inode *ea_inode,
> > struct ext4_xattr_entry *entry, void *buffer,
> > @@ -976,10 +984,8 @@ int __ext4_xattr_set_credits(struct super_block *sb, struct inode *inode,
> > static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode,
> > int ref_change)
> > {
> > - struct mb_cache *ea_inode_cache = EA_INODE_CACHE(ea_inode);
> > struct ext4_iloc iloc;
> > s64 ref_count;
> > - u32 hash;
> > int ret;
> >
> > inode_lock(ea_inode);
> > @@ -1002,14 +1008,6 @@ static int ext4_xattr_inode_update_ref(handle_t *handle, struct inode *ea_inode,
> >
> > set_nlink(ea_inode, 1);
> > ext4_orphan_del(handle, ea_inode);
> > -
> > - if (ea_inode_cache) {
> > - hash = ext4_xattr_inode_get_hash(ea_inode);
> > - mb_cache_entry_create(ea_inode_cache,
> > - GFP_NOFS, hash,
> > - ea_inode->i_ino,
> > - true /* reusable */);
> > - }
>
> Ok, so if I understand this correctly, since we are not immediately removing the
> ea_inode_cache entry when the recount reaches 0, hence when the refcount is
> reaches 1 from 0, we need not create mb_cache entry is it?
> Is this since the entry never got deleted in the first place?

Correct.

> But what happens when the entry is created the very first time?
> I might need to study xattr code to understand how this condition is
> taken care.

There are other places that take care of creating the entry in that case.
E.g. ext4_xattr_inode_get() or ext4_xattr_inode_lookup_create().

Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR