Re: netbsd-5-rc1 crash in pmap_enter

[Antti Kantee <pooka%cs.hut.fi@localhost>]

On Sat Feb 07 2009 at 00:04:13 +0100, 
6bone%6bone.informatik.uni-leipzig.de@localhost wrote:
> Hello list,
> 
> I am using an actual version of NetBSD 5.0_RC1 (amd). The kernel sometimes 
> crashes with:
> 
> panic: pmap_enter: pve allocation failed
> fatal breakpoint trap in supervisor mode
> trap type 1 code 0 rip ffffffff8051ecb5 cs 8 rflags 246 cr2  7f7ffd216104 
> cpl 00
> Stopped in pid 396.1 (postgres) at      netbsd:breakpoint+0x5:  leave
> db{0}> trace
> breakpoint() at netbsd:breakpoint+0x5
> panic() at netbsd:panic+0x24d
> pmap_enter() at netbsd:pmap_enter+0xc52
> genfs_directio() at netbsd:genfs_directio+0x237
>
> [snip]
> 
> Can anyone have a look at the code?

Looks like a simple temporary memory outage.  Is the machine under
heavy load?

Try this patch if you're brave (completely untested).  Comments from
anyone else?  I'm not sure if this is enough or if a more dramatic
backoff is required.

Index: genfs_io.c
===================================================================
RCS file: /cvsroot/src/sys/miscfs/genfs/genfs_io.c,v
retrieving revision 1.13.4.1
diff -p -u -r1.13.4.1 genfs_io.c
--- genfs_io.c  2 Nov 2008 23:08:56 -0000       1.13.4.1
+++ genfs_io.c  6 Feb 2009 23:20:36 -0000
@@ -1731,7 +1731,13 @@ genfs_do_directio(struct vmspace *vs, va
        for (poff = 0; poff < klen; poff += PAGE_SIZE) {
                rv = pmap_extract(upm, puva + poff, &pa);
                KASSERT(rv);
-               pmap_enter(kpm, kva + poff, pa, prot, prot | PMAP_WIRED);
+ retry:
+               if ((error = pmap_enter(kpm, kva + poff, pa, prot,
+                   prot | PMAP_WIRED | PMAP_CANFAIL)) != 0) {
+                       pmap_update(kpm);
+                       uvm_wait("genfs_directio");
+                       goto retry;
+               }
        }
        pmap_update(kpm);