Date: Sun, 15 Mar 2020 22:13:29 -0700 From: Chuck Silvers <chuq@chuq.com> To: Mark Johnston <markj@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org, glebius@freebsd.org Subject: Re: svn commit: r358597 - head/sys/kern Message-ID: <20200316051329.GA4598@spathi.chuq.com> In-Reply-To: <20200313234817.GA10027@spy> References: <202003040022.0240Mpm6074186@repo.freebsd.org> <20200313234817.GA10027@spy>
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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
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