Re: [PATCH 07/12] vhost-scsi: convert put_page() to put_user_page*()

On 7/23/19 9:25 PM, john.hubbard@gmail.com wrote:

From: Jérôme Glisse <redacted>

For pages that were retained via get_user_pages*(), release those pages
via the new put_user_page*() routines, instead of via put_page().

This is part a tree-wide conversion, as described in commit fc1d8e7cca2d
("mm: introduce put_user_page*(), placeholder versions").

Changes from Jérôme's original patch:

* Changed a WARN_ON to a BUG_ON.

Clearly, the above commit log has it backwards (this is quite my night
for typos).  Please read that as "changed a BUG_ON to a WARN_ON".

I'll correct the commit description in next iteration of this patchset.

...

+	/*
+	 * Here in all cases we should have an IOVEC which use GUP. If that is
+	 * not the case then we will wrongly call put_user_page() and the page
+	 * refcount will go wrong (this is in vhost_scsi_release_cmd())
+	 */
+	WARN_ON(!iov_iter_get_pages_use_gup(iter));
+

...

thanks,
-- 
John Hubbard
NVIDIA