Re: [PATCH 2/2 v2] ceph: use a xarray to record all the opened files for each inode

[Xiubo Li <xiubli@xxxxxxxxxx>]

On 14/11/2022 21:39, Jeff Layton wrote:
> On Mon, 2022-11-14 at 13:19 +0800, xiubli@xxxxxxxxxx wrote:
> > From: Xiubo Li <xiubli@xxxxxxxxxx>
> >
> > When releasing the file locks the fl->fl_file memory could be
> > already released by another thread in filp_close(), so we couldn't
> > depend on fl->fl_file to get the inode. Just use a xarray to record
> > the opened files for each inode.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > URL: https://tracker.ceph.com/issues/57986
> > Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> > ---
> >   fs/ceph/file.c  |  9 +++++++++
> >   fs/ceph/inode.c |  4 ++++
> >   fs/ceph/locks.c | 17 ++++++++++++++++-
> >   fs/ceph/super.h |  4 ++++
> >   4 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index 85afcbbb5648..cb4a9c52df27 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -231,6 +231,13 @@ static int ceph_init_file_info(struct inode *inode, struct file *file,
> >   			fi->flags |= CEPH_F_SYNC;
> >   
> >   		file->private_data = fi;
> > +
> > +		ret = xa_insert(&ci->i_opened_files, (unsigned long)file,
> > +				CEPH_FILP_AVAILABLE, GFP_KERNEL);
> > +		if (ret) {
> > +			kmem_cache_free(ceph_file_cachep, fi);
> > +			return ret;
> > +		}
> >   	}
> >   
> >   	ceph_get_fmode(ci, fmode, 1);
> > @@ -932,6 +939,8 @@ int ceph_release(struct inode *inode, struct file *file)
> >   		dout("release inode %p regular file %p\n", inode, file);
> >   		WARN_ON(!list_empty(&fi->rw_contexts));
> >   
> > +		xa_erase(&ci->i_opened_files, (unsigned long)file);
> > +
> >   		ceph_fscache_unuse_cookie(inode, file->f_mode & FMODE_WRITE);
> >   		ceph_put_fmode(ci, fi->fmode, 1);
> >   
> > diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> > index 77b0cd9af370..554450838e44 100644
> > --- a/fs/ceph/inode.c
> > +++ b/fs/ceph/inode.c
> > @@ -619,6 +619,8 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
> >   	INIT_LIST_HEAD(&ci->i_unsafe_iops);
> >   	spin_lock_init(&ci->i_unsafe_lock);
> >   
> > +	xa_init(&ci->i_opened_files);
> > +
> >   	ci->i_snap_realm = NULL;
> >   	INIT_LIST_HEAD(&ci->i_snap_realm_item);
> >   	INIT_LIST_HEAD(&ci->i_snap_flush_item);
> > @@ -637,6 +639,8 @@ void ceph_free_inode(struct inode *inode)
> >   {
> >   	struct ceph_inode_info *ci = ceph_inode(inode);
> >   
> > +	xa_destroy(&ci->i_opened_files);
> > +
> >   	kfree(ci->i_symlink);
> >   #ifdef CONFIG_FS_ENCRYPTION
> >   	kfree(ci->fscrypt_auth);
> > diff --git a/fs/ceph/locks.c b/fs/ceph/locks.c
> > index d8385dd0076e..a176a30badd0 100644
> > --- a/fs/ceph/locks.c
> > +++ b/fs/ceph/locks.c
> > @@ -42,9 +42,10 @@ static void ceph_fl_copy_lock(struct file_lock *dst, struct file_lock *src)
> >   
> >   static void ceph_fl_release_lock(struct file_lock *fl)
> >   {
> > -	struct ceph_file_info *fi = fl->fl_file->private_data;
> >   	struct inode *inode = fl->fl_u.ceph_fl.fl_inode;
> >   	struct ceph_inode_info *ci;
> > +	struct ceph_file_info *fi;
> > +	void *val;
> >   
> >   	/*
> >   	 * If inode is NULL it should be a request file_lock,
> > @@ -54,6 +55,20 @@ static void ceph_fl_release_lock(struct file_lock *fl)
> >   		return;
> >   
> >   	ci = ceph_inode(inode);
> > +
> > +	/*
> > +	 * For Posix-style locks, it may race between filp_close()s,
> > +	 * and it's possible that the 'file' memory pointed by
> > +	 * 'fl->fl_file' has been released. If so just skip it.
> > +	 */
> > +	rcu_read_lock();
> > +	val = xa_load(&ci->i_opened_files, (unsigned long)fl->fl_file);
> > +	if (val == CEPH_FILP_AVAILABLE) {
> > +		fi = fl->fl_file->private_data;
> > +		atomic_dec(&fi->num_locks);
> Don't you need to remove the old atomic_dec from this function if you
> move it here?

Yeah, I thought I have removed that. Not sure why I added it back.

> > +	}
> > +	rcu_read_unlock();
> > +
> >   	if (atomic_dec_and_test(&ci->i_filelock_ref)) {
> >   		/* clear error when all locks are released */
> >   		spin_lock(&ci->i_ceph_lock);
> > diff --git a/fs/ceph/super.h b/fs/ceph/super.h
> > index 7b75a84ba48d..b3e89192cbec 100644
> > --- a/fs/ceph/super.h
> > +++ b/fs/ceph/super.h
> > @@ -329,6 +329,8 @@ struct ceph_inode_xattrs_info {
> >   	u64 version, index_version;
> >   };
> >   
> > +#define CEPH_FILP_AVAILABLE         xa_mk_value(1)
> > +
> >   /*
> >    * Ceph inode.
> >    */
> > @@ -434,6 +436,8 @@ struct ceph_inode_info {
> >   	struct list_head i_unsafe_iops;   /* uncommitted mds inode ops */
> >   	spinlock_t i_unsafe_lock;
> >   
> > +	struct xarray		i_opened_files;
> > +
> >   	union {
> >   		struct ceph_snap_realm *i_snap_realm; /* snap realm (if caps) */
> >   		struct ceph_snapid_map *i_snapid_map; /* snapid -> dev_t */
> This looks like it'll work, but it's a lot of extra work, having to
> track this extra xarray just on the off chance that one of these fd's
> might have file locks. The num_locks field is only checked in one place
> in ceph_get_caps.
>
> Here's what I'd recommend instead:
>
> Have ceph_get_caps look at the lists in inode->i_flctx and see whether
> any of its locks have an fl_file that matches the @filp argument in that
> function. Most inodes never get any file locks, so in most cases  this
> will turn out to just be a NULL pointer check for i_flctx anyway.
>
> Then you can just remove the num_locks field and call the new helper
> from ceph_get_caps instead. I'll send along a proposed patch for the
> helper in a bit.

Sure, Thanks Jeff.

- Xiubo