debugging frequent kernel panics on 8.2-RELEASE

[Andriy Gapon]

on 19/08/2011 15:14 John Baldwin said the following:
> Yes, it is a bug in kgdb that it only walks allproc and not zombproc.  Try this:

The patch worked perfectly well for me, thank you!

> Index: kthr.c
> ===================================================================
> --- kthr.c	(revision 224879)
> +++ kthr.c	(working copy)
> @@ -73,11 +73,52 @@ kgdb_thr_first(void)
>  	return (first);
>  }
>  
> +static void
> +kgdb_thr_add_procs(uintptr_t paddr)
> +{
> +	struct proc p;
> +	struct thread td;
> +	struct kthr *kt;
> +	CORE_ADDR addr;
> +
> +	while (paddr != 0) {
> +		if (kvm_read(kvm, paddr, &p, sizeof(p)) != sizeof(p)) {
> +			warnx("kvm_read: %s", kvm_geterr(kvm));
> +			break;
> +		}
> +		addr = (uintptr_t)TAILQ_FIRST(&p.p_threads);
> +		while (addr != 0) {
> +			if (kvm_read(kvm, addr, &td, sizeof(td)) !=
> +			    sizeof(td)) {
> +				warnx("kvm_read: %s", kvm_geterr(kvm));
> +				break;
> +			}
> +			kt = malloc(sizeof(*kt));
> +			kt->next = first;
> +			kt->kaddr = addr;
> +			if (td.td_tid == dumptid)
> +				kt->pcb = dumppcb;
> +			else if (td.td_state == TDS_RUNNING && stoppcbs != 0 &&
> +			    CPU_ISSET(td.td_oncpu, &stopped_cpus))
> +				kt->pcb = (uintptr_t)stoppcbs +
> +				    sizeof(struct pcb) * td.td_oncpu;
> +			else
> +				kt->pcb = (uintptr_t)td.td_pcb;
> +			kt->kstack = td.td_kstack;
> +			kt->tid = td.td_tid;
> +			kt->pid = p.p_pid;
> +			kt->paddr = paddr;
> +			kt->cpu = td.td_oncpu;
> +			first = kt;
> +			addr = (uintptr_t)TAILQ_NEXT(&td, td_plist);
> +		}
> +		paddr = (uintptr_t)LIST_NEXT(&p, p_list);
> +	}
> +}
> +
>  struct kthr *
>  kgdb_thr_init(void)
>  {
> -	struct proc p;
> -	struct thread td;
>  	long cpusetsize;
>  	struct kthr *kt;
>  	CORE_ADDR addr;
> @@ -113,37 +154,11 @@ kgdb_thr_init(void)
>  
>  	stoppcbs = kgdb_lookup("stoppcbs");
>  
> -	while (paddr != 0) {
> -		if (kvm_read(kvm, paddr, &p, sizeof(p)) != sizeof(p)) {
> -			warnx("kvm_read: %s", kvm_geterr(kvm));
> -			break;
> -		}
> -		addr = (uintptr_t)TAILQ_FIRST(&p.p_threads);
> -		while (addr != 0) {
> -			if (kvm_read(kvm, addr, &td, sizeof(td)) !=
> -			    sizeof(td)) {
> -				warnx("kvm_read: %s", kvm_geterr(kvm));
> -				break;
> -			}
> -			kt = malloc(sizeof(*kt));
> -			kt->next = first;
> -			kt->kaddr = addr;
> -			if (td.td_tid == dumptid)
> -				kt->pcb = dumppcb;
> -			else if (td.td_state == TDS_RUNNING && stoppcbs != 0 &&
> -			    CPU_ISSET(td.td_oncpu, &stopped_cpus))
> -				kt->pcb = (uintptr_t) stoppcbs + sizeof(struct pcb) * td.td_oncpu;
> -			else
> -				kt->pcb = (uintptr_t)td.td_pcb;
> -			kt->kstack = td.td_kstack;
> -			kt->tid = td.td_tid;
> -			kt->pid = p.p_pid;
> -			kt->paddr = paddr;
> -			kt->cpu = td.td_oncpu;
> -			first = kt;
> -			addr = (uintptr_t)TAILQ_NEXT(&td, td_plist);
> -		}
> -		paddr = (uintptr_t)LIST_NEXT(&p, p_list);
> +	kgdb_thr_add_procs(paddr);
> +	addr = kgdb_lookup("zombproc");
> +	if (addr != 0) {
> +		kvm_read(kvm, addr, &paddr, sizeof(paddr));
> +		kgdb_thr_add_procs(paddr);
>  	}
>  	curkthr = kgdb_thr_lookup_tid(dumptid);
>  	if (curkthr == NULL)
> 
>> is there an easy way to examine its stack in this case?
> 
> Hmm, you can use something like this from my kgdb macros.

Oh, I completely forgot about them.
I hope I will remember where to search for the tricks next time I need them :-)
Thank you again!

> For amd64:
> 
> # Do a backtrace given %rip and %rbp as args
> define bt
>     set $_rip = $arg0
>     set $_rbp = $arg1
>     set $i = 0
>     while ($_rbp != 0 || $_rip != 0)
> 	printf "%2d: pc ", $i
> 	if ($_rip != 0)
> 		x/1i $_rip
> 	else
> 		printf "\n"
> 	end
> 	if ($_rbp == 0)
> 	    set $_rip = 0
> 	else
> 	    set $fr = (struct amd64_frame *)$_rbp
> 	    set $_rbp = $fr->f_frame
> 	    set $_rip = $fr->f_retaddr
> 	    set $i = $i + 1
> 	end
>     end
> end
> 
> document bt
> Given values for %rip and %rbp, perform a manual backtrace.
> end
> 
> define btf
>     bt $arg0.tf_rip $arg0.tf_rbp
> end
> 
> document btf
> Do a manual backtrace from a specified trapframe.
> end
> 
> For i386:
> 
> # Do a backtrace given %eip and %ebp as args
> define bt
>     set $_eip = $arg0
>     set $_ebp = $arg1
>     set $i = 0
>     while ($_ebp != 0 || $_eip != 0)
> 	printf "%2d: pc ", $i
> 	if ($_eip != 0)
> 		x/1i $_eip
> 	else
> 		printf "\n"
> 	end
> 	if ($_ebp == 0)
> 	    set $_eip = 0
> 	else
> 	    set $fr = (struct i386_frame *)$_ebp
> 	    set $_ebp = $fr->f_frame
> 	    set $_eip = $fr->f_retaddr
> 	    set $i = $i + 1
> 	end
>     end
> end
> 
> document bt
> Given values for %eip and %ebp, perform a manual backtrace.
> end
> 
> define btf
>     bt $arg0.tf_eip $arg0.tf_ebp
> end
> 
> document btf
> Do a manual backtrace from a specified trapframe.
> end
> 


-- 
Andriy Gapon