Messages in this thread | | | Date | Wed, 2 Mar 2022 11:22:29 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: boot flooded with unwind: Index not found |
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On Wed, Mar 02, 2022 at 12:19:40PM +0100, Ard Biesheuvel wrote: > On Wed, 2 Mar 2022 at 12:12, Russell King (Oracle) > <linux@armlinux.org.uk> wrote: > > > > On Wed, Mar 02, 2022 at 11:09:49AM +0100, Corentin Labbe wrote: > > > The crash disappeared (but the suspicious RCU usage is still here). > > > > As the trace on those is: > > > > [ 0.239629] unwind_backtrace from show_stack+0x10/0x14 > > [ 0.239654] show_stack from init_stack+0x1c54/0x2000 > > > > unwind_backtrace() and show_stack() are both C code, the compiler will > > emit the unwind information for it. show_stack() isn't called from > > assembly code, only from C code, so the next function's unwind > > information should also be generated by the compiler. > > > > However, init_stack is not a function - it's an array of unsigned long. > > There is no way this should appear in the trace, and this suggests that > > the unwind of show_stack() has gone wrong. > > > > I don't see anything obvious in Ard's changes that would cause that > > though. > > > > Did it used to work fine with previous versions of linux-next - those > > versions where we had Ard's "arm-vmap-stacks-v6" tag merged in > > (commit 2fa394824493) and did this only appear when I merged > > "arm-ftrace-for-rmk" (commit 74aaaa1e9bba) ? Did merging > > "arm-ftrace-for-rmk" cause any change in your .config? > > > > I can reproduce the RCU warnings, and I have tracked this down to the > change I made to return_address() for the graph tracer, which I > thought was justified after removing the call to > kernel_text_address(): > > --- a/arch/arm/include/asm/ftrace.h > +++ b/arch/arm/include/asm/ftrace.h > @@ -35,26 +35,8 @@ static inline unsigned long > ftrace_call_adjust(unsigned long addr) > > #ifndef __ASSEMBLY__ > > -#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) > -/* > - * return_address uses walk_stackframe to do it's work. If both > - * CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind > - * information. For this to work in the function tracer many functions would > - * have to be marked with __notrace. So for now just depend on > - * !CONFIG_ARM_UNWIND. > - */ > - > void *return_address(unsigned int); > > -#else > - > -static inline void *return_address(unsigned int level) > -{ > - return NULL; > -} > - > -#endif > - > #define ftrace_return_address(n) return_address(n) > > #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME > > However, the function graph tracer works happily with this bit > reverted, and so that is probably the best course of action here. > > I have already sent the patch that reintroduces the > kernel_text_address() check - would you prefer a v2 of that one with > this change incorporated? Or a second patch that just reverts the > above? (Given that the bogus dereference was invoked from > return_address() as well, I suspect that this change would make the > get_kernel_nofault() change I proposed in this thread redundant)
I'd prefer patches on top of my devel-stable branch, thanks.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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