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smb: client: introduce close_cached_dir_locked() #109

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smb: client: introduce close_cached_dir_locked() #109

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41 changes: 38 additions & 3 deletions fs/smb/client/cached_dir.c
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Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,7 @@ static struct cached_fid *init_cached_dir(const char *path);
static void free_cached_dir(struct cached_fid *cfid);
static void smb2_close_cached_fid(struct kref *ref);
static void cfids_laundromat_worker(struct work_struct *work);
static void close_cached_dir_locked(struct cached_fid *cfid);

struct cached_dir_dentry {
struct list_head entry;
Expand Down Expand Up @@ -388,7 +389,7 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
* lease. Release one here, and the second below.
*/
cfid->has_lease = false;
close_cached_dir(cfid);
close_cached_dir_locked(cfid);
}
spin_unlock(&cfids->cfid_list_lock);

Expand Down Expand Up @@ -480,18 +481,52 @@ void drop_cached_dir_by_name(const unsigned int xid, struct cifs_tcon *tcon,
spin_lock(&cfid->cfids->cfid_list_lock);
if (cfid->has_lease) {
cfid->has_lease = false;
close_cached_dir(cfid);
close_cached_dir_locked(cfid);
}
spin_unlock(&cfid->cfids->cfid_list_lock);
close_cached_dir(cfid);
}


/**
* close_cached_dir - drop a reference of a cached dir
*
* The release function will be called with cfid_list_lock held to remove the
* cached dirs from the list before any other thread can take another @cfid
* ref. Must not be called with cfid_list_lock held; use
* close_cached_dir_locked() called instead.
*
* @cfid: cached dir
*/
void close_cached_dir(struct cached_fid *cfid)
{
lockdep_assert_not_held(&cfid->cfids->cfid_list_lock);
kref_put_lock(&cfid->refcount, smb2_close_cached_fid, &cfid->cfids->cfid_list_lock);
}

/**
* close_cached_dir_locked - put a reference of a cached dir with
* cfid_list_lock held
*
* Calling close_cached_dir() with cfid_list_lock held has the potential effect
* of causing a deadlock if the invariant of refcount >= 2 is false.
*
* This function is used in paths that hold cfid_list_lock and expect at least
* two references. If that invariant is violated, WARNs and returns without
* dropping a reference; the final put must still go through
* close_cached_dir().
*
* @cfid: cached dir
*/
static void close_cached_dir_locked(struct cached_fid *cfid)
{
lockdep_assert_held(&cfid->cfids->cfid_list_lock);

if (WARN_ON(kref_read(&cfid->refcount) < 2))
return;

kref_put(&cfid->refcount, smb2_close_cached_fid);
}

/*
* Called from cifs_kill_sb when we unmount a share
*/
Expand Down