Hi,
On Sun, May 11, 2008 at 9:44 PM, Arjan van de Ven <arjan@linux.intel.com> wrote:
...
Okay, this is slightly emberrassing. I made a new test, here's the output:
dump_stack():
[<ffffffff8062b021>] do_page_fault+0x31/0x70
[<ffffffff80224195>] ? cpa_fill_pool+0x135/0x140
[<ffffffff80224c40>] ? change_page_attr_set_clr+0x1c0/0x220
[<ffffffff80220a21>] ? address_get_pte+0x11/0x30
[<ffffffff80628fb9>] error_exit+0x0/0x51
[<ffffffff8028655a>] ? __slab_alloc+0x35a/0x560
[<ffffffff80286556>] ? __slab_alloc+0x356/0x560
[<ffffffff80386535>] ? kvasprintf+0x55/0x90
[<ffffffff80287809>] ? __kmalloc+0xf9/0x110
[<ffffffff80386535>] ? kvasprintf+0x55/0x90
[<ffffffff8038660b>] ? kasprintf+0x9b/0xa0
[<ffffffff802898ba>] ? create_kmalloc_cache+0xaa/0xe0
[<ffffffff80898193>] ? kmem_cache_init+0xf3/0x170
[<ffffffff80882b35>] ? start_kernel+0x245/0x340
[<ffffffff80882457>] ? x86_64_start_kernel+0x257/0x290
save_stack_trace()/print_stack_trace():
[<ffffffff80213eca>] save_stack_trace+0x2a/0x50
[<ffffffff8062b049>] do_page_fault+0x59/0x70
[<ffffffff80628fb9>] error_exit+0x0/0x51
[<ffffffffffffffff>] 0xffffffffffffffff
And what seems now immediately clear is that the difference is that
the latter doesn't print the unreliable stack frames. Which reminds me
that *I* was the person who submitted the patch to do that:
commit 1650743cdc0db73478f72c57544ce79ea8f3dda6
Author: Vegard Nossum <vegard.nossum@gmail.com>
Date: Fri Feb 22 19:23:58 2008 +0100
x86: don't save unreliable stack trace entries
Currently, there is no way for print_stack_trace() to determine whether
a given stack trace entry was deemed reliable or not, simply because
save_stack_trace() does not record this information. (Perhaps needless
to say, this makes the saved stack traces A LOT harder to read, and
probably with no other benefits, since debugging features that use
save_stack_trace() most likely also require frame pointers, etc.)
This patch reverts to the old behaviour of only recording the reliable trace
entries for saved stack traces.
Signed-off-by: Vegard Nossum <vegardno@ifi.uio.no>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Still, this seems to be the better behaviour (that patch should not be
reverted), and I think it's the tracer itself that should be fixed to
not mark these entries as unreliable, like the 32-bit version
apparently does.
I did send a patch in february that would allow the reliability of
frames to be saved along with the frames themselves, though it had no
replies:
http://lkml.org/lkml/2008/2/23/173
Would you reconsider this patch, or provide some feedback if it needs
to be improved? In the meantime, I will make some attempts at making
the pre-pagefault frames be seen as reliable :-)
Thanks.
Vegard
--
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036
--
