Re: what is this KASSERT() testing?

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Mon, Dec 6, 2010 at 4:48 PM, Antti Kantee <pooka%cs.hut.fi@localhost> wrote:
> On Mon Dec 06 2010 at 11:55:05 +1100, matthew green wrote:
>>
>> hi.
>>
>>
>> my devbox just crashed with this:
>>
>> panic: kernel diagnostic assertion "pg == NULL || pg == PGO_DONTCARE" 
>> failed: file "/usr/src/sys/miscfs/genfs/genfs_io.c", line 243
>>
>> but i don't understand the KASSERT().  it seems that this sequence
>> of events will always trigger:
>>
>>                 nfound = uvn_findpages(uobj, origoffset, &npages,
>>                     ap->a_m, UFP_NOWAIT|UFP_NOALLOC|(memwrite ? UFP_NORDONLY 
>> : 0));
>> ...
>>                 if (!genfs_node_rdtrylock(vp)) {
>> ...
>>                         for (i = 0; i < npages; i++) {
>>                                 pg = ap->a_m[i];
>>                                 if (pg != NULL && pg != PGO_DONTCARE) {
>>                                         ap->a_m[i] = NULL;
>>                                 }
>>
>>                                 KASSERT(pg == NULL || pg == PGO_DONTCARE);
>>
>> won't all pages filled in by the uvn_findpages() be not NULL, so
>> if the uvn_findpages() succeeds but the genfs_node_rdtrylock()
>> fails, we will trigger this assert always.
>>
>>
>> i think it should just be removed.
>
> I guess it wants to test ap->a_m[i], cf. the change to the assignment
> clause in the same revision.

You're right!