On Wed, 30 Sep 2009 14:49:25 -0400,
Takao Indoh <indou.takao at jp.fujitsu.com> wrote:
>Hi all,
>
>When I was investigating vmcore captured by kdump, I noticed that
>the backtrace was sometimes not displayed correctly.
>
>The cause is that pt_regs and switch_stack are not saved in the stack
>when INIT comes during fsys mode. In fsys mode, r13 register does not
>point task_struct of current, so pt_regs and switch_stack are not saved
>because of the following code in arch/ia64/kernel/mca.c.
>
>static struct task_struct *
>ia64_mca_modify_original_stack(struct pt_regs *regs,
>(snip)
> if (r13 != sos->prev_IA64_KR_CURRENT) {
> msg = "inconsistent previous current and r13";
> goto no_mod;
> }
>
>What I'd like to note here is that there is no way to know what happened
>when original stack is not modified.
>As I wrote above, the registers is not saved in the original stack, and
>moreover, the registers in the per cpu stack are useless since they are
>incomplete. We can't know why backtrace is not displayed. The only thing
>we can get is the message "inconsistent previous current and r13" in the
>mprintk buffer. Something problem happened? Or kernel was just in fsys
>mode? We cannot know.
>
>Solution1:
> The pt_regs in the per cpu stack are incomplete, so fill in the blanks
> with the appropriate registers so that we can debug using them.
>
>Solution2:
> Save the processor min-state(pal_min_state_area_t) somewhere. When
> debugging, user can get register info from it.
>
>I prefer solution1 because it's easy for user to debug. The
>following patch is for solution1. restore_regs(), which is new function
>added by this patch, is just copying registers from pal_min_state
>to pt_regs.
>
>Any comments would be appreciated.
>
>Thanks,
>Takao Indoh
>
>Signed-off-by: Takao Indoh <indou.takao at jp.fujitsu.com>
>---
> arch/ia64/kernel/mca.c | 103 +++++++++++++++++++++------------------
> 1 file changed, 56 insertions(+), 47 deletions(-)
>
>diff -Nurp linux-2.6.31.org/arch/ia64/kernel/mca.c linux-2.6.31/arch/ia64/kernel/mca.c
>--- linux-2.6.31.org/arch/ia64/kernel/mca.c 2009-09-21 17:12:45.000000000 -0400
>+++ linux-2.6.31/arch/ia64/kernel/mca.c 2009-09-24 16:15:05.000000000 -0400
>@@ -887,6 +887,60 @@ ia64_mca_modify_comm(const struct task_s
> memcpy(current->comm, comm, sizeof(current->comm));
> }
>
>+static void
>+restore_regs(struct pt_regs *regs, const pal_min_state_area_t *ms,
>+ unsigned long *nat)
The name 'restore_regs' is too generic and is used in other code,
'finish_pt_regs' might be better.
>+{
>+ const u64 *bank;
>+
>+ /* If ipsr.ic then use pmsa_{iip,ipsr,ifs}, else use
>+ * pmsa_{xip,xpsr,xfs}
>+ */
>+ if (ia64_psr(regs)->ic) {
>+ regs->cr_iip = ms->pmsa_iip;
>+ regs->cr_ipsr = ms->pmsa_ipsr;
>+ regs->cr_ifs = ms->pmsa_ifs;
>+ } else {
>+ regs->cr_iip = ms->pmsa_xip;
>+ regs->cr_ipsr = ms->pmsa_xpsr;
>+ regs->cr_ifs = ms->pmsa_xfs;
>+ }
>+ regs->pr = ms->pmsa_pr;
>+ regs->b0 = ms->pmsa_br0;
>+ regs->ar_rsc = ms->pmsa_rsc;
>+ copy_reg(&ms->pmsa_gr[1-1], ms->pmsa_nat_bits, ®s->r1, nat);
>+ copy_reg(&ms->pmsa_gr[2-1], ms->pmsa_nat_bits, ®s->r2, nat);
>+ copy_reg(&ms->pmsa_gr[3-1], ms->pmsa_nat_bits, ®s->r3, nat);
>+ copy_reg(&ms->pmsa_gr[8-1], ms->pmsa_nat_bits, ®s->r8, nat);
>+ copy_reg(&ms->pmsa_gr[9-1], ms->pmsa_nat_bits, ®s->r9, nat);
>+ copy_reg(&ms->pmsa_gr[10-1], ms->pmsa_nat_bits, ®s->r10, nat);
>+ copy_reg(&ms->pmsa_gr[11-1], ms->pmsa_nat_bits, ®s->r11, nat);
>+ copy_reg(&ms->pmsa_gr[12-1], ms->pmsa_nat_bits, ®s->r12, nat);
>+ copy_reg(&ms->pmsa_gr[13-1], ms->pmsa_nat_bits, ®s->r13, nat);
>+ copy_reg(&ms->pmsa_gr[14-1], ms->pmsa_nat_bits, ®s->r14, nat);
>+ copy_reg(&ms->pmsa_gr[15-1], ms->pmsa_nat_bits, ®s->r15, nat);
>+ if (ia64_psr(regs)->bn)
>+ bank = ms->pmsa_bank1_gr;
>+ else
>+ bank = ms->pmsa_bank0_gr;
>+ copy_reg(&bank[16-16], ms->pmsa_nat_bits, ®s->r16, nat);
>+ copy_reg(&bank[17-16], ms->pmsa_nat_bits, ®s->r17, nat);
>+ copy_reg(&bank[18-16], ms->pmsa_nat_bits, ®s->r18, nat);
>+ copy_reg(&bank[19-16], ms->pmsa_nat_bits, ®s->r19, nat);
>+ copy_reg(&bank[20-16], ms->pmsa_nat_bits, ®s->r20, nat);
>+ copy_reg(&bank[21-16], ms->pmsa_nat_bits, ®s->r21, nat);
>+ copy_reg(&bank[22-16], ms->pmsa_nat_bits, ®s->r22, nat);
>+ copy_reg(&bank[23-16], ms->pmsa_nat_bits, ®s->r23, nat);
>+ copy_reg(&bank[24-16], ms->pmsa_nat_bits, ®s->r24, nat);
>+ copy_reg(&bank[25-16], ms->pmsa_nat_bits, ®s->r25, nat);
>+ copy_reg(&bank[26-16], ms->pmsa_nat_bits, ®s->r26, nat);
>+ copy_reg(&bank[27-16], ms->pmsa_nat_bits, ®s->r27, nat);
>+ copy_reg(&bank[28-16], ms->pmsa_nat_bits, ®s->r28, nat);
>+ copy_reg(&bank[29-16], ms->pmsa_nat_bits, ®s->r29, nat);
>+ copy_reg(&bank[30-16], ms->pmsa_nat_bits, ®s->r30, nat);
>+ copy_reg(&bank[31-16], ms->pmsa_nat_bits, ®s->r31, nat);
>+}
>+
> /* On entry to this routine, we are running on the per cpu stack, see
> * mca_asm.h. The original stack has not been touched by this event. Some of
> * the original stack's registers will be in the RBS on this stack. This stack
>@@ -921,7 +975,6 @@ ia64_mca_modify_original_stack(struct pt
> u64 r12 = ms->pmsa_gr[12-1], r13 = ms->pmsa_gr[13-1];
> u64 ar_bspstore = regs->ar_bspstore;
> u64 ar_bsp = regs->ar_bspstore + (loadrs >> 16);
>- const u64 *bank;
> const char *msg;
> int cpu = smp_processor_id();
>
>@@ -1024,54 +1077,9 @@ ia64_mca_modify_original_stack(struct pt
> p = (char *)r12 - sizeof(*regs);
> old_regs = (struct pt_regs *)p;
> memcpy(old_regs, regs, sizeof(*regs));
>- /* If ipsr.ic then use pmsa_{iip,ipsr,ifs}, else use
>- * pmsa_{xip,xpsr,xfs}
>- */
>- if (ia64_psr(regs)->ic) {
>- old_regs->cr_iip = ms->pmsa_iip;
>- old_regs->cr_ipsr = ms->pmsa_ipsr;
>- old_regs->cr_ifs = ms->pmsa_ifs;
>- } else {
>- old_regs->cr_iip = ms->pmsa_xip;
>- old_regs->cr_ipsr = ms->pmsa_xpsr;
>- old_regs->cr_ifs = ms->pmsa_xfs;
>- }
>- old_regs->pr = ms->pmsa_pr;
>- old_regs->b0 = ms->pmsa_br0;
> old_regs->loadrs = loadrs;
>- old_regs->ar_rsc = ms->pmsa_rsc;
> old_unat = old_regs->ar_unat;
>- copy_reg(&ms->pmsa_gr[1-1], ms->pmsa_nat_bits, &old_regs->r1, &old_unat);
>- copy_reg(&ms->pmsa_gr[2-1], ms->pmsa_nat_bits, &old_regs->r2, &old_unat);
>- copy_reg(&ms->pmsa_gr[3-1], ms->pmsa_nat_bits, &old_regs->r3, &old_unat);
>- copy_reg(&ms->pmsa_gr[8-1], ms->pmsa_nat_bits, &old_regs->r8, &old_unat);
>- copy_reg(&ms->pmsa_gr[9-1], ms->pmsa_nat_bits, &old_regs->r9, &old_unat);
>- copy_reg(&ms->pmsa_gr[10-1], ms->pmsa_nat_bits, &old_regs->r10, &old_unat);
>- copy_reg(&ms->pmsa_gr[11-1], ms->pmsa_nat_bits, &old_regs->r11, &old_unat);
>- copy_reg(&ms->pmsa_gr[12-1], ms->pmsa_nat_bits, &old_regs->r12, &old_unat);
>- copy_reg(&ms->pmsa_gr[13-1], ms->pmsa_nat_bits, &old_regs->r13, &old_unat);
>- copy_reg(&ms->pmsa_gr[14-1], ms->pmsa_nat_bits, &old_regs->r14, &old_unat);
>- copy_reg(&ms->pmsa_gr[15-1], ms->pmsa_nat_bits, &old_regs->r15, &old_unat);
>- if (ia64_psr(old_regs)->bn)
>- bank = ms->pmsa_bank1_gr;
>- else
>- bank = ms->pmsa_bank0_gr;
>- copy_reg(&bank[16-16], ms->pmsa_nat_bits, &old_regs->r16, &old_unat);
>- copy_reg(&bank[17-16], ms->pmsa_nat_bits, &old_regs->r17, &old_unat);
>- copy_reg(&bank[18-16], ms->pmsa_nat_bits, &old_regs->r18, &old_unat);
>- copy_reg(&bank[19-16], ms->pmsa_nat_bits, &old_regs->r19, &old_unat);
>- copy_reg(&bank[20-16], ms->pmsa_nat_bits, &old_regs->r20, &old_unat);
>- copy_reg(&bank[21-16], ms->pmsa_nat_bits, &old_regs->r21, &old_unat);
>- copy_reg(&bank[22-16], ms->pmsa_nat_bits, &old_regs->r22, &old_unat);
>- copy_reg(&bank[23-16], ms->pmsa_nat_bits, &old_regs->r23, &old_unat);
>- copy_reg(&bank[24-16], ms->pmsa_nat_bits, &old_regs->r24, &old_unat);
>- copy_reg(&bank[25-16], ms->pmsa_nat_bits, &old_regs->r25, &old_unat);
>- copy_reg(&bank[26-16], ms->pmsa_nat_bits, &old_regs->r26, &old_unat);
>- copy_reg(&bank[27-16], ms->pmsa_nat_bits, &old_regs->r27, &old_unat);
>- copy_reg(&bank[28-16], ms->pmsa_nat_bits, &old_regs->r28, &old_unat);
>- copy_reg(&bank[29-16], ms->pmsa_nat_bits, &old_regs->r29, &old_unat);
>- copy_reg(&bank[30-16], ms->pmsa_nat_bits, &old_regs->r30, &old_unat);
>- copy_reg(&bank[31-16], ms->pmsa_nat_bits, &old_regs->r31, &old_unat);
>+ restore_regs(old_regs, ms, &old_unat);
>
> /* Next stack a struct switch_stack. mca_asm.S built a partial
> * switch_stack, copy it and fill in the blanks using pt_regs and
>@@ -1141,6 +1149,7 @@ ia64_mca_modify_original_stack(struct pt
> no_mod:
> mprintk(KERN_INFO "cpu %d, %s %s, original stack not modified\n",
> smp_processor_id(), type, msg);
>+ restore_regs(regs, ms, &old_unat);
old_unat is undefined here. You need
old_unat = regs->ar_unat;
> return previous_current;
> }
The rest of it looks good.
