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Commit 2557a933 authored Apr 07, 2008 by Rusty Russell Committed by Linus Torvalds Apr 07, 2008

virtio: remove overzealous BUG_ON.



The 'disable_cb' callback is designed as an optimization to tell the host
we don't need callbacks now.  As it is not reliable, the debug check is
overzealous: it can happen on two CPUs at the same time.  Document this.

Even if it were reliable, the virtio_net driver doesn't disable
callbacks on transmit so the START_USE/END_USE debugging reentrance
protection can be easily tripped even on UP.

Thanks to Balaji Rao for the bug report and testing.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
CC: Balaji Rao <balajirrao@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4cac04dd

drivers/virtio/virtio_ring.c

+0 −3

Original line number	Original line	Diff line number	Diff line
	@@ -214,10 +214,7 @@ static void vring_disable_cb(struct virtqueue *_vq)
	{		{
	struct vring_virtqueue *vq = to_vvq(_vq);		struct vring_virtqueue *vq = to_vvq(_vq);

	START_USE(vq);
	BUG_ON(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
	vq->vring.avail->flags \|= VRING_AVAIL_F_NO_INTERRUPT;		vq->vring.avail->flags \|= VRING_AVAIL_F_NO_INTERRUPT;
	END_USE(vq);
	}		}

	static bool vring_enable_cb(struct virtqueue *_vq)		static bool vring_enable_cb(struct virtqueue *_vq)

include/linux/virtio.h

+4 −1

Original line number	Original line	Diff line number	Diff line
	@@ -41,6 +41,8 @@ struct virtqueue
	* Returns NULL or the "data" token handed to add_buf.		* Returns NULL or the "data" token handed to add_buf.
	* @disable_cb: disable callbacks		* @disable_cb: disable callbacks
	* vq: the struct virtqueue we're talking about.		* vq: the struct virtqueue we're talking about.
			* Note that this is not necessarily synchronous, hence unreliable and only
			* useful as an optimization.
	* @enable_cb: restart callbacks after disable_cb.		* @enable_cb: restart callbacks after disable_cb.
	* vq: the struct virtqueue we're talking about.		* vq: the struct virtqueue we're talking about.
	* This re-enables callbacks; it returns "false" if there are pending		* This re-enables callbacks; it returns "false" if there are pending
	@@ -48,7 +50,8 @@ struct virtqueue
	* checking for more work, and enabling callbacks.		* checking for more work, and enabling callbacks.
	*		*
	* Locking rules are straightforward: the driver is responsible for		* Locking rules are straightforward: the driver is responsible for
	* locking. No two operations may be invoked simultaneously.		* locking. No two operations may be invoked simultaneously, with the exception
			* of @disable_cb.
	*		*
	* All operations can be called in any context.		* All operations can be called in any context.
	*/		*/