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SubjectRe: stack unwinder warning.
On Fri, Jan 06, 2017 at 12:09:47AM -0500, Dave Jones wrote:
> On Thu, Jan 05, 2017 at 11:02:14AM -0600, Josh Poimboeuf wrote:
> > On Thu, Jan 05, 2017 at 08:52:49AM -0600, Josh Poimboeuf wrote:
> > > On Tue, Dec 27, 2016 at 02:00:30PM -0500, Dave Jones wrote:
> > > > I'm not sure what to make of this. Josh ? (4.10-rc1)
> > > >
> > > > WARNING: kernel stack frame pointer at ffffc900003e7858 in trinity-c6:29122 has bad value ffffffff82103a80
> > > > unwind stack type:0 next_sp: (null) mask:2 graph_idx:0
> > > > ffffc900003e7808: ffffffff811a02e5 (ring_buffer_lock_reserve+0x1d5/0x580)
> > > > ffffc900003e7810: ffffffff8119adc3 (rb_commit+0x93/0x350)
> > > > ffffc900003e7818: ffffffff811b31d4 (function_trace_call+0x104/0x1f0)
> > > > ffffc900003e7820: ffff8804f10ec000 (0xffff8804f10ec000)
> > > > ffffc900003e7828: 0000000000000000 ...
> > > > ffffc900003e7830: ffffffff8119b3ae (ring_buffer_unlock_commit+0x8e/0x120)
> > > > ffffc900003e7838: 0000000000000001 (0x1)
> > > > ffffc900003e7840: ffffea0002854e00 (0xffffea0002854e00)
> > > > ffffc900003e7848: 000000000000000a (0xa)
> > > > ffffc900003e7850: ffffea0002854ec0 (0xffffea0002854ec0)
> > > > ffffc900003e7858: ffffea000287c480 (0xffffea000287c480)
> > >
> > > The value reported by the warning contradicts the value reported by the
> > > dump. So this seems to have been caused by dumping the stack of a task
> > > which is running on another CPU. There are still some places in the
> > > code where that's possible. So I'm going to need to remove these
> > > unwinder warnings for now.
> >
> > I'll be submitting the following patch soon, which I think should
> > silence the warning. If the warning is recreatable, would you mind
> > testing it?
>
> I didn't wait long enough..
>
> WARNING: kernel stack frame pointer at ffffc90001443f30 in kworker/u8:8:30468 has bad value (null)
> unwind stack type:0 next_sp: (null) mask:6 graph_idx:0

This is actually a separate issue. The below patch should fix it.

Would you mind running it for a bit along with the other patch?


diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 5b21970..044d18e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -36,6 +36,7 @@
#include <asm/smap.h>
#include <asm/pgtable_types.h>
#include <asm/export.h>
+#include <asm/frame.h>
#include <linux/err.h>

.code64
@@ -408,17 +409,19 @@ END(__switch_to_asm)
* r12: kernel thread arg
*/
ENTRY(ret_from_fork)
+ FRAME_BEGIN /* help unwinder find end of stack */
movq %rax, %rdi
- call schedule_tail /* rdi: 'prev' task parameter */
+ call schedule_tail /* rdi: 'prev' task parameter */

- testq %rbx, %rbx /* from kernel_thread? */
- jnz 1f /* kernel threads are uncommon */
+ testq %rbx, %rbx /* from kernel_thread? */
+ jnz 1f /* kernel threads are uncommon */

2:
- movq %rsp, %rdi
+ leaq FRAME_OFFSET(%rsp),%rdi /* pt_regs pointer */
call syscall_return_slowpath /* returns with IRQs disabled */
TRACE_IRQS_ON /* user mode is traced as IRQS on */
SWAPGS
+ FRAME_END
jmp restore_regs_and_iret

1:
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