forked from Minki/linux
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: 0e67db2f9f
("kernfs: add kernfs_ops->open/release() callbacks")
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
63f1ca5945
commit
f83f3c5156
@ -747,10 +747,15 @@ err_out:
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static void kernfs_release_file(struct kernfs_node *kn,
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struct kernfs_open_file *of)
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{
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if (!(kn->flags & KERNFS_HAS_RELEASE))
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return;
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/*
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* @of is guaranteed to have no other file operations in flight and
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* we just want to synchronize release and drain paths.
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* @kernfs_open_file_mutex is enough. @of->mutex can't be used
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* here because drain path may be called from places which can
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* cause circular dependency.
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*/
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lockdep_assert_held(&kernfs_open_file_mutex);
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mutex_lock(&of->mutex);
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if (!of->released) {
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/*
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* A file is never detached without being released and we
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@ -760,7 +765,6 @@ static void kernfs_release_file(struct kernfs_node *kn,
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kn->attr.ops->release(of);
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of->released = true;
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}
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mutex_unlock(&of->mutex);
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}
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static int kernfs_fop_release(struct inode *inode, struct file *filp)
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@ -768,7 +772,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
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struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
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struct kernfs_open_file *of = kernfs_of(filp);
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kernfs_release_file(kn, of);
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if (kn->flags & KERNFS_HAS_RELEASE) {
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mutex_lock(&kernfs_open_file_mutex);
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kernfs_release_file(kn, of);
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mutex_unlock(&kernfs_open_file_mutex);
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}
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kernfs_put_open_node(kn, of);
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seq_release(inode, filp);
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kfree(of->prealloc_buf);
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