svn commit: r358597 - head/sys/kern

[Chuck Silvers]

On Fri, Mar 13, 2020 at 07:48:17PM -0400, Mark Johnston wrote:
> On Wed, Mar 04, 2020 at 12:22:51AM +0000, Chuck Silvers wrote:
> > Author: chs
> > Date: Wed Mar  4 00:22:50 2020
> > New Revision: 358597
> > URL: https://svnweb.freebsd.org/changeset/base/358597
> > 
> > Log:
> >   if vm_pager_get_pages_async() returns an error, release the sfio->nios
> >   refcount that we took earlier that represents the I/O that ended up
> >   not being started.
> 
> I think a larger bug is that getpages_async is not consistent about
> whether it invokes the completion callback in synchronous error cases.
> For instance, vop_stdgetpages_async() always calls it, as does
> ffs_getpages_async() when the filesystem fragment size is larger than
> the page size.  But vnode_pager_generic_getpages() does not.  So if one
> is using sendfile on a filesystem that does not implement
> getpages_async, an error will cause sendfile_swapin() to unbusy the
> input pages multiple times, and release the sfio refcount twice when it
> should be done just once.


ah yes, you're right.  I was only looking at the path we actually hit.

I think the simplest way to resolve this would be to change
vnode_pager_generic_getpages() in the async case to always
call the iodone callback and always return 0.  (in the sync case
vnode_pager_generic_getpages() would continue to return an error code
if an error is encountered.)  vm_pager_get_pages_async() could then
be changed to return void since after the avoid changes it would
always return 0.  swap_pager_getpages_async() already always calls
the iodone callback but it would return void too after the above changes.

If that is agreeable to you and Gleb then I'll make the changes.

-Chuck