Re: pmap_qenter() - the page *must* be wired - is violated

2011/10/6 Kostik Belousov <kostikbel_at_gmail.com>:
> On Thu, Oct 06, 2011 at 01:45:16PM +0200, Svatopluk Kraus wrote:
>> On Wed, Oct 5, 2011 at 4:53 PM, Kostik Belousov <kostikbel_at_gmail.com> wrote:
>> > On Wed, Oct 05, 2011 at 02:28:01PM +0200, Svatopluk Kraus wrote:
>> >> Hi,
>> >>
>> >>   I found out that on a few places pmap_qenter() is called on pages
>> >> which are not wired. For example, in the following functions, when
>> >> vm_pager_get_pages() is called, the pages are not wired:
>> >>
>> >>   exec_map_first_page() in sys/kern/kern_exec.c
>> >>   vm_fault_hold() in sys/vm/vm_fault.c
>> >>   vm_imgact_hold_page() in sys/vm/vm_glue.c
>> >>   vm_object_populate() in sys/vm/vm_object.c
>> >>   mdstart_swap() in sys/dev/md/md.c
>> >>
>> >>   Is the rule violated or the rule should be changed?
>> >
>> > Lets first discuss where did you found the calls to pmap_qenter().
>> > Can you point out exact line numbers of the calls to pmap_qenter()
>> > that you consider problematic ?
>> >
>> > In fact, the requirement probably shall be 'no swapout allowed'. E.g.,
>> > the busy page is fully qualified to be used together with pmap_qenter().
>>
>> Well, I just follow description above pmap_qenter() blindly and test for
>> page wire_count inside the function. All function calls, I mentioned before,
>> are OK as pages are VPO_BUSY'd. Thanks for your explanation.
> Still, I am not aware of any (direct) calls to pmap_qenter in the mentioned
> functions.
>

The functions allocate page(s) and then call vm_pager_get_pages()
which calling stack could be be following:

vnode_pager_getpages()
VOP_GETPAGES()
vop_stdgetpages()
vnode_pager_generic_getpages()
pmap_qenter()

or for fs/nfsclient:
VOP_GETPAGES()
ncl_getpages()
pmap_qenter()

Many file systems call pmap_qenter() in their .vop_getpages implementation.