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

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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





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