Re: [PATCH 01/12] VMCI: context implementation.
From: Greg KH <gregkh@linuxfoundation.org>
Date: 2012-10-30 02:10:05
Also in:
lkml
On Mon, Oct 29, 2012 at 06:03:42PM -0700, George Zhang wrote:
quoted hunk ↗ jump to hunk
+/* + * Releases the VMCI context. If this is the last reference to + * the context it will be deallocated. A context is created with + * a reference count of one, and on destroy, it is removed from + * the context list before its reference count is + * decremented. Thus, if we reach zero, we are sure that nobody + * else are about to increment it (they need the entry in the + * context list for that). This function musn't be called with a + * lock held. + */ +void vmci_ctx_release(struct vmci_ctx *context) +{ + ASSERT(context); + kref_put(&context->kref, ctx_free_ctx); +} +
Hm, are you _sure_ you should be calling this without a lock held? That's usually kref-101, you MUST hold a lock when calling put, otherwise you can race a kref_get() call, and all hell can break loose. Because of this, some saner people (like Al Viro), have suggested that I force the kref_put() and kref_get() calls pass in a spinlock just to enforce this. So, tell me what I'm missing here, and why you put the comment here saying that it really is supposed to be called without a lock held? How is that safe? confused, greg k-h