Messages in this thread Patch in this message | | | From | Ard Biesheuvel <> | Date | Wed, 2 Mar 2022 12:19:40 +0100 | Subject | Re: boot flooded with unwind: Index not found |
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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)
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