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smb: client: introduce close_cached_dir_locked()

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commit a9d1f38df7 upstream.

Replace close_cached_dir() calls under cfid_list_lock with a new
close_cached_dir_locked() variant that uses kref_put() instead of
kref_put_lock() to avoid recursive locking when dropping references.

While the existing code works if the refcount >= 2 invariant holds,
this area has proven error-prone. Make deadlocks impossible and WARN
on invariant violations.

Cc: stable@vger.kernel.org
Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Henrique Carvalho <henrique.carvalho@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Henrique Carvalho
2025-11-13 15:09:13 -03:00
committed by Greg Kroah-Hartman
parent 21879b7683
commit 8d7a5b0e5a
1 changed files with 38 additions and 3 deletions
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41
fs/smb/client/cached_dir.c
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@@ -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;
@@ -389,7 +390,7 @@ out:
* 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);
@@ -476,18 +477,52 @@ 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
*/