Re: [Crash-utility] Kernel pages reported as PAGE_EXCLUDED
----- Original Message -----
Hi,
I'm analyzing a dump file ("KDUMP" header) with crash 7.0.1 that seems
to have some kernel pages missing:
crash> struct foo ffff81101e19e000
struct foo struct: page excluded: kernel virtual address: ffff81101e19e000
type: "gdb_readmem_callback"
Cannot access memory at address 0xffff81101e19e000
When I set debug to 1 it turns out that even crash's 'mount' command
hits excluded pages:
mount: page excluded: kernel virtual address: ffff81101d688000 type: "read_string
characters"
In order to understand this error better I took a look at
diskdump.c:read_diskdump():
if (!page_is_dumpable(pfn)) {
if ((dd->flags & (ZERO_EXCLUDED|ERROR_EXCLUDED)) ==
ERROR_EXCLUDED) {
if (CRASHDEBUG(8))
fprintf(fp, "read_diskdump: PAGE_EXCLUDED: "
"paddr/pfn: %llx/%lx\n",
(ulonglong)paddr, pfn);
return PAGE_EXCLUDED;
}
if (CRASHDEBUG(8))
fprintf(fp, "read_diskdump: zero-fill: "
"paddr/pfn: %llx/%lx\n",
(ulonglong)paddr, pfn);
memset(bufptr, 0, cnt);
return cnt;
}
Does this mean these kernel pages are *not* zero?
No, it means that if you invoke crash with the --zero_excluded flag,
if an excluded page is encountered during runtime, it will return
a zero-filled page instead of erroring out.
Why would kernel pages containing structs (i.e. not page cache or
userspace pages) be excluded from the dump file?
They wouldn't -- or better put -- shouldn't ever be excluded.
(This may seem like a weird question but I did not generate the dump
file myself so I can't easily try recreating it with different options.)
Thanks,
Stefan
The only explanation I can think of off the top of my head is if perhaps
the page structures that makedumpfile parses were corrupted such that
they were mistakenly presumed to be filter-worthy?
Just a guess -- anybody else have any ideas of how it could happen?
Dave