Hi Vineet, any chance you could look at this? Otherwise we will both forget what it is all about :) On Tue, 2018-08-07 at 16:59 +0300, Eugeniy Paltsev wrote: > We process signals in the end of syscall/exception handler. > It the signal is fatal we print register's content using > show_regs function. show_regs() also prints information about > last exception happened. > > In case of multicore system we can catch the situation when we > will print wrong information about exception. See the example: > ______________________________ > CPU-0: started to handle page fault > CPU-1: sent signal to process, which is executed on CPU-0 > CPU-0: ended page fault handle. Started to process signal before > returnig to userspace. Process signal, which is send from > CPU-0. As th signal is fatal we call show_regs(). > show_regs() will show information about last exception > which is *page fault* (instead of "trap" which is used for > signals and happened on CPU-0) > > So we will get message like this: > # ./waitpid02 > potentially unexpected fatal signal 8. > Path: /home/waitpid02 > CPU: 0 PID: 100 Comm: waitpid02 Not tainted 4.10.0-rc4 #2 > task: 9f11c200 task.stack: 9f3ae000 > > [ECR ]: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x000123ec > [EFA ]: 0x00000000 > [BLINK ]: 0x123ea > [ERET ]: 0x123ec > @off 0x123ec in [/home/waitpid02] > VMA: 0x00010000 to 0x00016000 > [STAT32]: 0x80080882 : IE U > BTA: 0x000123ea SP: 0x5ffd3db0 FP: 0x00000000 > LPS: 0x20031684 LPE: 0x2003169a LPC: 0x00000006 > [-----other-info-----] > > This message is confusing because it show information about page fault > ( [ECR ]: 0x00050200 => Invalid Write ) which is absolutely irrelevant > to signal. > > This situation was reproduced with waitpid02 LTP test. > _____________________________ > > So remove printing information about exceptions from show_regs() > to avoid confusing messages. Print information about exceptions > only in required places instead of show_regs() > > Now we don't print information about exceptions if signal is simply > send by another userspace app. So in case of waitpid02 we will print > next message: > _____________________________ > # ./waitpid02 > potentially unexpected fatal signal 8. > Path: /root/waitpid02 > CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17 > [ECR ]: 0x00050100 > [EFA ]: 0x00000000 > [BLINK ]: 0x20001486 > [-----other-info-----] > _____________________________ > > This patch fix > STAR 9001146055: waitpid02: Invalid Write @ 0x00000000 by insn @ 0x000123ec > > NOTE: > To be more clear I give examples of different faults (signal-based, > userspace/kernelspace exception-based) with different values of > "/proc/sys/kernel/print-fatal-signals" option. > > 0) NULL pointer access from user space, print-fatal-signals == 1: > ------------>8--------------- > # ./arc_hell > Exception: arc_hell[103]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000] > ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c > potentially unexpected fatal signal 11. > Path: /root/arc_hell > CPU: 1 PID: 103 Comm: arc_hell Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17 > [ECR ]: 0x00050100 > [EFA ]: 0x00000000 > [BLINK ]: 0x20039ef8 > [ERET ]: 0x2003a35c > [STAT32]: 0x80080882 : IE U > BTA: 0x2003a358 SP: 0x5fa27dc4 FP: 0x5fa27de8 > LPS: 0x2003a628 LPE: 0x2003a62c LPC: 0x00000000 > r00: 0x00000000 r01: 0x200740b0 r02: 0x00000001 > r03: 0x00000007 r04: 0x80808080 r05: 0x2f2f2f2f > r06: 0x7c7a2f43 r07: 0x00000000 r08: 0x1a131100 > r09: 0x2008b1e0 r10: 0x20003a5c r11: 0x20004038 > r12: 0x20039ef8 r13: 0x200740b0 r14: 0x00000000 > r15: 0x200740b0 r16: 0x00000000 r17: 0x0007d468 > r18: 0x0009313a r19: 0x00000000 r20: 0x0009c22c > r21: 0x0009c23c r22: 0x0009ab64 r23: 0x00000000 > r24: 0x0009dfc5 r25: 0x20004b70 > > Segmentation fault > ------------>8--------------- > > 1) NULL pointer access from user space, print-fatal-signals == 0: > ------------>8--------------- > # ./arc_hell > Exception: arc_hell[107]: at 0x2003a35c [off 0x2e35c in /lib/libuClibc-1.0.18.so, VMA: 2000c000:20072000] > ECR: 0x00050100 => Invalid Read @ 0x00000000 by insn @ 0x2003a35c > Segmentation fault > ------------>8--------------- > > 2) Process killed by signal (waitpid02 test), print-fatal-signals == 1: > ------------>8--------------- > # ./waitpid02 > potentially unexpected fatal signal 8. > Path: /root/waitpid02 > CPU: 2 PID: 105 Comm: waitpid02 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #17 > [ECR ]: 0x00050100 > [EFA ]: 0x00000000 > [BLINK ]: 0x20001486 > [ERET ]: 0x2000146c > [STAT32]: 0x80080082 : IE U > BTA: 0x20000fc4 SP: 0x5fa21d64 FP: 0x00000000 > LPS: 0x200524a0 LPE: 0x200524b6 LPC: 0x00000006 > r00: 0x2000c0dc r01: 0x00000018 r02: 0x0001159a > r03: 0x00000001 r04: 0x00000000 r05: 0x00000045 > r06: 0x0000004e r07: 0x01010101 r08: 0x000000dc > r09: 0x200a31e0 r10: 0x20003a5c r11: 0x20004038 > r12: 0x20001486 r13: 0x20004174 r14: 0x07ca2bc0 > r15: 0x20004078 r16: 0x00000000 r17: 0x20004038 > r18: 0x00000001 r19: 0x00000000 r20: 0x0001159a > r21: 0x00000001 r22: 0x00000000 r23: 0x00000004 > r24: 0x2000d1fc r25: 0x20004cd0 > ------------>8--------------- > > 3) Process killed by signal (waitpid02 test), print-fatal-signals == 0: > ------------>8--------------- > # ./waitpid02 > ------------>8--------------- > > 4) NULL pointer access from kernel space, regardless print-fatal-signals > value: > ------------>8--------------- > Oops > Exception: at stmmac_dvr_probe+0x40/0x7e0: > ECR: 0x00050200 => Invalid Write @ 0x00000000 by insn @ 0x90575254 > Path: (null) > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.0-rc8-00002-gde0f6d6aeb53-dirty #11 > [EFA ]: 0x00000000 > [BLINK ]: stmmac_dvr_probe+0x2a/0x7e0 > [ERET ]: stmmac_dvr_probe+0x40/0x7e0 > [STAT32]: 0x80080402 : IE K > BTA: 0x9057523e SP: 0xbf02be40 FP: 0x00000000 > LPS: 0x9073dbcc LPE: 0x9073dbe0 LPC: 0x00000000 > r00: 0xbf1f0000 r01: 0x00000000 r02: 0x00000008 > r03: 0x00000000 r04: 0x00000064 r05: 0x00000000 > r06: 0x00000003 r07: 0x00000004 r08: 0x01010101 > r09: 0x00000031 r10: 0xbf1f0006 r11: 0x00000000 > r12: 0x9057523e > > Stack Trace: > stmmac_dvr_probe+0x40/0x7e0 > dwmac_generic_probe+0x50/0xbc > platform_drv_probe+0x26/0x5c > really_probe+0x3b0/0x464 > __driver_attach+0xd4/0xd8 > bus_for_each_dev+0x3a/0x70 > bus_add_driver+0x12a/0x18c > driver_register+0x56/0xe8 > do_one_initcall+0x2e/0x118 > kernel_init_freeable+0x102/0x194 > ------------>8--------------- > > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev at synopsys.com> > --- > > NOTE: > This patch has prerequisites: > https://www.mail-archive.com/linux-snps-arc at lists.infradead.org/msg03938.html > https://www.mail-archive.com/linux-snps-arc at lists.infradead.org/msg03937.html > > Changes v1->v2: > * Change format of message about exception. > > arch/arc/include/asm/bug.h | 1 + > arch/arc/kernel/traps.c | 1 + > arch/arc/kernel/troubleshoot.c | 51 +++++++++++++++++++++++++++++++++--------- > arch/arc/mm/fault.c | 2 ++ > 4 files changed, 44 insertions(+), 11 deletions(-) > > diff --git a/arch/arc/include/asm/bug.h b/arch/arc/include/asm/bug.h > index 21ec82466d62..b68f7f82f2d8 100644 > --- a/arch/arc/include/asm/bug.h > +++ b/arch/arc/include/asm/bug.h > @@ -16,6 +16,7 @@ > struct task_struct; > > void show_regs(struct pt_regs *regs); > +void show_exception_mesg(struct pt_regs *regs); > void show_stacktrace(struct task_struct *tsk, struct pt_regs *regs); > void show_kernel_fault_diag(const char *str, struct pt_regs *regs, > unsigned long address); > diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c > index b123558bf0bb..5d83b2fe5f12 100644 > --- a/arch/arc/kernel/traps.c > +++ b/arch/arc/kernel/traps.c > @@ -50,6 +50,7 @@ unhandled_exception(const char *str, struct pt_regs *regs, siginfo_t *info) > tsk->thread.fault_address = (__force unsigned int)info->si_addr; > > force_sig_info(info->si_signo, info, tsk); > + show_exception_mesg(regs); > > } else { > /* If not due to copy_(to|from)_user, we are doomed */ > diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c > index e8d9fb452346..fdfba1942a06 100644 > --- a/arch/arc/kernel/troubleshoot.c > +++ b/arch/arc/kernel/troubleshoot.c > @@ -101,13 +101,13 @@ static void show_faulting_vma(unsigned long address, char *buf) > if (IS_ERR(nm)) > nm = "?"; > } > - pr_info(" @off 0x%lx in [%s]\n" > - " VMA: 0x%08lx to 0x%08lx\n", > + > + pr_cont("[off 0x%lx in %s, VMA: %08lx:%08lx] ", > vma->vm_start < TASK_UNMAPPED_BASE ? > address : address - vma->vm_start, > nm, vma->vm_start, vma->vm_end); > } else > - pr_info(" @No matching VMA found\n"); > + pr_cont("[No matching VMA found] "); > > up_read(&active_mm->mmap_sem); > } > @@ -117,7 +117,7 @@ static void show_ecr_verbose(struct pt_regs *regs) > unsigned int vec, cause_code; > unsigned long address; > > - pr_info("\n[ECR ]: 0x%08lx => ", regs->event); > + pr_cont("\n ECR: 0x%08lx => ", regs->event); > > /* For Data fault, this is data address not instruction addr */ > address = current->thread.fault_address; > @@ -165,10 +165,42 @@ static void show_ecr_verbose(struct pt_regs *regs) > } > } > > +static inline void show_exception_mesg_u(struct pt_regs *regs) > +{ > + struct task_struct *tsk = current; > + char *buf; > + > + pr_info("Exception: %s[%d]: at %pS ", > + tsk->comm, task_pid_nr(tsk), (void *)regs->ret); > + > + buf = (char *)__get_free_page(GFP_NOWAIT); > + if (buf) { > + show_faulting_vma(regs->ret, buf); > + free_page((unsigned long)buf); > + } > + > + show_ecr_verbose(regs); > +} > + > +static inline void show_exception_mesg_k(struct pt_regs *regs) > +{ > + pr_info("Exception: at %pS:", (void *)regs->ret); > + > + show_ecr_verbose(regs); > +} > + > /************************************************************************ > * API called by rest of kernel > ***********************************************************************/ > > +void show_exception_mesg(struct pt_regs *regs) > +{ > + if (user_mode(regs)) > + show_exception_mesg_u(regs); > + else > + show_exception_mesg_k(regs); > +} > + > void show_regs(struct pt_regs *regs) > { > struct task_struct *tsk = current; > @@ -182,15 +214,10 @@ void show_regs(struct pt_regs *regs) > print_task_path_n_nm(tsk, buf); > show_regs_print_info(KERN_INFO); > > - show_ecr_verbose(regs); > - > - pr_info("[EFA ]: 0x%08lx\n[BLINK ]: %pS\n[ERET ]: %pS\n", > - current->thread.fault_address, > + pr_info("[ECR ]: 0x%08lx\n[EFA ]: 0x%08lx\n[BLINK ]: %pS\n[ERET ]: %pS\n", > + regs->event, current->thread.fault_address, > (void *)regs->blink, (void *)regs->ret); > > - if (user_mode(regs)) > - show_faulting_vma(regs->ret, buf); /* faulting code, not data */ > - > pr_info("[STAT32]: 0x%08lx", regs->status32); > > #define STS_BIT(r, bit) r->status32 & STATUS_##bit##_MASK ? #bit" " : "" > @@ -233,6 +260,8 @@ void show_kernel_fault_diag(const char *str, struct pt_regs *regs, > /* Show fault description */ > pr_info("\n%s\n", str); > > + show_exception_mesg(regs); > + > /* Caller and Callee regs */ > show_regs(regs); > > diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c > index b884bbd6f354..d9c6958a1702 100644 > --- a/arch/arc/mm/fault.c > +++ b/arch/arc/mm/fault.c > @@ -202,6 +202,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs) > /* info.si_code has been set above */ > info.si_addr = (void __user *)address; > force_sig_info(SIGSEGV, &info, tsk); > + show_exception_mesg(regs); > return; > } > > @@ -241,4 +242,5 @@ void do_page_fault(unsigned long address, struct pt_regs *regs) > info.si_code = BUS_ADRERR; > info.si_addr = (void __user *)address; > force_sig_info(SIGBUS, &info, tsk); > + show_exception_mesg(regs); > } -- Eugeniy Paltsev
