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authorTejun Heo <tj@kernel.org>2017-02-12 05:33:02 +0900
committerTejun Heo <tj@kernel.org>2017-02-21 15:49:25 -0500
commitf83f3c515654474e19c7fc86e3b06564bb5cb4d4 (patch)
tree17389a81a3e78f0051e4fb5d948f3d440f539cce
parent63f1ca59453aadae81f702840c7ac6ea8b9f9262 (diff)
kernfs: fix locking around kernfs_ops->release() callback
The release callback may be called from two places - file release operation and kernfs open file draining. kernfs_open_file->mutex is used to synchronize the two callsites. This unfortunately leads to possible circular locking because of->mutex is used to protect the usual kernfs operations which may use locking constructs which are held while removing and thus draining kernfs files. @of->mutex is for synchronizing concurrent kernfs access operations and all we need here is synchronization between the releaes and drain paths. As the drain path has to grab kernfs_open_file_mutex anyway, let's use the mutex to synchronize the release operation instead. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-tested-by: Tony Lindgren <tony@atomide.com> Fixes: 0e67db2f9fe9 ("kernfs: add kernfs_ops->open/release() callbacks") Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/kernfs/file.c19
1 files changed, 14 insertions, 5 deletions
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 20c396291ac1..14da136028de 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -747,10 +747,15 @@ err_out:
static void kernfs_release_file(struct kernfs_node *kn,
struct kernfs_open_file *of)
{
- if (!(kn->flags & KERNFS_HAS_RELEASE))
- return;
+ /*
+ * @of is guaranteed to have no other file operations in flight and
+ * we just want to synchronize release and drain paths.
+ * @kernfs_open_file_mutex is enough. @of->mutex can't be used
+ * here because drain path may be called from places which can
+ * cause circular dependency.
+ */
+ lockdep_assert_held(&kernfs_open_file_mutex);
- mutex_lock(&of->mutex);
if (!of->released) {
/*
* A file is never detached without being released and we
@@ -760,7 +765,6 @@ static void kernfs_release_file(struct kernfs_node *kn,
kn->attr.ops->release(of);
of->released = true;
}
- mutex_unlock(&of->mutex);
}
static int kernfs_fop_release(struct inode *inode, struct file *filp)
@@ -768,7 +772,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
struct kernfs_open_file *of = kernfs_of(filp);
- kernfs_release_file(kn, of);
+ if (kn->flags & KERNFS_HAS_RELEASE) {
+ mutex_lock(&kernfs_open_file_mutex);
+ kernfs_release_file(kn, of);
+ mutex_unlock(&kernfs_open_file_mutex);
+ }
+
kernfs_put_open_node(kn, of);
seq_release(inode, filp);
kfree(of->prealloc_buf);