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    SubjectRe: 4.14.9 doesn't boot (regression)
    On Sat, Dec 30, 2017 at 11:09:46AM -0600, Josh Poimboeuf wrote:
    > On Sat, Dec 30, 2017 at 11:45:13AM +0300, Alexander Tsoy wrote:
    > > В Пт, 29/12/2017 в 21:49 -0600, Josh Poimboeuf пишет:
    > > > On Fri, Dec 29, 2017 at 05:10:35PM -0700, Andy Lutomirski wrote:
    > > > > (Also, Josh, the oops code should have printed the contents of the
    > > > > struct pt_regs at the top of the DF stack.  Any idea why it
    > > > > didn't?)
    > > >
    > > > Looking at one of the dumps:
    > > >
    > > >   [  392.774879] NMI backtrace for cpu 0
    > > >   [  392.774881] CPU: 0 PID: 1 Comm: init Not tainted 4.14.9-gentoo
    > > > #1
    > > >   [  392.774881] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
    > > >   [  392.774882] task: ffff8802368b8000 task.stack: ffffc9000000c000
    > > >   [  392.774885] RIP: 0010:double_fault+0x0/0x30
    > > >   [  392.774886] RSP: 0000:ffffffffff527fd0 EFLAGS: 00000086
    > > >   [  392.774887] RAX: 000000003fc00000 RBX: 0000000000000001 RCX:
    > > > 00000000c0000101
    > > >   [  392.774887] RDX: 00000000ffff8802 RSI: 0000000000000000 RDI:
    > > > ffffffffff527f58
    > > >   [  392.774887] RBP: 0000000000000000 R08: 0000000000000000 R09:
    > > > 0000000000000000
    > > >   [  392.774888] R10: 0000000000000000 R11: 0000000000000000 R12:
    > > > ffffffff816ae726
    > > >   [  392.774888] R13: 0000000000000000 R14: 0000000000000000 R15:
    > > > 0000000000000000
    > > >   [  392.774889] FS:  0000000000000000(0000)
    > > > GS:ffff88023fc00000(0000) knlGS:0000000000000000
    > > >   [  392.774889] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > > >   [  392.774890] CR2: ffffffffff526f08 CR3: 0000000235b48002 CR4:
    > > > 00000000001606f0
    > > >   [  392.774892] Call Trace:
    > > >   [  392.774894]  <#DF>
    > > >   [  392.774897]  do_double_fault+0xb/0x140
    > > >   [  392.774898]  </#DF>
    > > >
    > > > It should have at least printed the #DF iret frame registers, which I
    > > > recently added support for in "x86/unwinder: Handle stack overflows
    > > > more
    > > > gracefully", which is in both 4.14.9 and 4.15-rc5.
    > > >
    > > > I think the missing iret regs are due to a bug in
    > > > show_trace_log_lvl(),
    > > > where if the unwind starts with two regs frames in a row, the second
    > > > regs don't get printed.
    > > >
    > > > Alexander, would you mind reproducing again with the below patch?  It
    > > > should still fail, but this time it should hopefully show another
    > > > RIP/RSP/EFLAGS instead of the "do_double_fault+0xb/0x140" line.
    > > >
    > >
    > > Yes, it works:
    > >
    > > [   23.058064] NMI backtrace for cpu 2
    > > [   23.058068] CPU: 2 PID: 1 Comm: init Not tainted 4.15.0-rc5+ #1
    > > [   23.058069] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
    > > BIOS 1.10.2-1.fc27 04/01/2014
    > > [   23.058074] RIP: 0010:double_fault+0x0/0x30
    > > [   23.058075] RSP: 0000:fffffe800005ffd0 EFLAGS: 00000086
    > > [   23.058077] RAX: 000000003fd00000 RBX: 0000000000000001 RCX:
    > > 00000000c0000101
    > > [   23.058077] RDX: 00000000ffff9681 RSI: 0000000000000000 RDI:
    > > fffffe800005ff58
    > > [   23.058078] RBP: 0000000000000000 R08: 0000000000000000 R09:
    > > 0000000000000000
    > > [   23.058079] R10: 0000000000000000 R11: 0000000000000000 R12:
    > > ffffffff92001426
    > > [   23.058080] R13: 0000000000000000 R14: 0000000000000000 R15:
    > > 0000000000000000
    > > [   23.058083] FS:  0000000000000000(0000) GS:ffff96813fd00000(0000)
    > > knlGS:0000000000000000
    > > [   23.058084] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    > > [   23.058085] CR2: fffffe800005ef08 CR3: 0000000137a09000 CR4:
    > > 00000000000406a0
    > > [   23.058089] Call Trace:
    > > [   23.058101]  <#DF>
    > > [   23.058104] RIP: 0010:do_double_fault+0xb/0x140
    > > [   23.058105] RSP: 0000:fffffe800005ef18 EFLAGS: 00010086 ORIG_RAX:
    > > 0000000000000000
    > > [   23.058106] RAX: 000000003fd00000 RBX: 0000000000000001 RCX:
    > > 00000000c0000101
    > > [   23.058107] RDX: 00000000ffff9681 RSI: 0000000000000000 RDI:
    > > fffffe800005ff58
    > > [   23.058107] RBP: 0000000000000000 R08: 0000000000000000 R09:
    > > 0000000000000000
    > > [   23.058108] R10: 0000000000000000 R11: 0000000000000000 R12:
    > > ffffffff92001426
    > > [   23.058108] R13: 0000000000000000 R14: 0000000000000000 R15:
    > > 0000000000000000
    > > [   23.058111]  </#DF>
    > > [   23.058111] Code: 05 00 00 48 89 e7 31 f6 e8 2e 8c 61 ff e9 69 06 00
    > > 00 e8 94 05 00 00 48 89 e7 31 f6 e8 1a 8c 61 ff e9 55 06 00 00 0f 1f 44
    > > 00 00 <0f> 1f 00 48 83 c4 88 e8 e4 04 00 00 48 89 e7 48 8b 74 24 78 48
    >
    > That's better indeed, though still not quite right. It should have only
    > shown a subset of those registers. One more bug to fix there...

    Turns out my previous code to print iret frames was a bit ... misguided,
    to put it nicely. Not sure what I was smoking.

    Hopefully the below patch should fix it (in place of the previous
    patch). Would you mind testing again?

    diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
    index c1688c2d0a12..1f86e1b0a5cd 100644
    --- a/arch/x86/include/asm/unwind.h
    +++ b/arch/x86/include/asm/unwind.h
    @@ -56,18 +56,27 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,

    #if defined(CONFIG_UNWINDER_ORC) || defined(CONFIG_UNWINDER_FRAME_POINTER)
    /*
    - * WARNING: The entire pt_regs may not be safe to dereference. In some cases,
    - * only the iret frame registers are accessible. Use with caution!
    + * If 'partial' returns true, only the iret frame registers are valid.
    */
    -static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
    +static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state,
    + bool *partial)
    {
    if (unwind_done(state))
    return NULL;

    + if (partial) {
    +#ifdef CONFIG_UNWINDER_ORC
    + *partial = !state->full_regs;
    +#else
    + *partial = false;
    +#endif
    + }
    +
    return state->regs;
    }
    #else
    -static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
    +static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state,
    + bool *partial)
    {
    return NULL;
    }
    diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
    index 36b17e0febe8..6e49d2e0c243 100644
    --- a/arch/x86/kernel/dumpstack.c
    +++ b/arch/x86/kernel/dumpstack.c
    @@ -76,12 +76,11 @@ void show_iret_regs(struct pt_regs *regs)
    regs->sp, regs->flags);
    }

    -static void show_regs_safe(struct stack_info *info, struct pt_regs *regs)
    +static void show_regs_full_or_partial(struct pt_regs *regs, bool partial)
    {
    - if (on_stack(info, regs, sizeof(*regs)))
    + if (!partial)
    __show_regs(regs, 0);
    - else if (on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
    - IRET_FRAME_SIZE)) {
    + else {
    /*
    * When an interrupt or exception occurs in entry code, the
    * full pt_regs might not have been saved yet. In that case
    @@ -98,11 +97,13 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
    struct stack_info stack_info = {0};
    unsigned long visit_mask = 0;
    int graph_idx = 0;
    + bool partial;

    printk("%sCall Trace:\n", log_lvl);

    unwind_start(&state, task, regs, stack);
    stack = stack ? : get_stack_pointer(task, regs);
    + regs = unwind_get_entry_regs(&state, &partial);

    /*
    * Iterate through the stacks, starting with the current stack pointer.
    @@ -120,7 +121,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
    * - hardirq stack
    * - entry stack
    */
    - for (regs = NULL; stack; stack = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
    + for ( ; stack; stack = PTR_ALIGN(stack_info.next_sp, sizeof(long))) {
    const char *stack_name;

    if (get_stack_info(stack, task, &stack_info, &visit_mask)) {
    @@ -140,7 +141,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
    printk("%s <%s>\n", log_lvl, stack_name);

    if (regs)
    - show_regs_safe(&stack_info, regs);
    + show_regs_full_or_partial(regs, partial);

    /*
    * Scan the stack, printing any text addresses we find. At the
    @@ -164,7 +165,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,

    /*
    * Don't print regs->ip again if it was already printed
    - * by show_regs_safe() below.
    + * by show_regs_full_or_partial() below.
    */
    if (regs && stack == &regs->ip)
    goto next;
    @@ -199,9 +200,9 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
    unwind_next_frame(&state);

    /* if the frame has entry regs, print them */
    - regs = unwind_get_entry_regs(&state);
    + regs = unwind_get_entry_regs(&state, &partial);
    if (regs)
    - show_regs_safe(&stack_info, regs);
    + show_regs_full_or_partial(regs, partial);
    }

    if (stack_name)
    diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
    index 77835bc021c7..7dd0d2a0d142 100644
    --- a/arch/x86/kernel/stacktrace.c
    +++ b/arch/x86/kernel/stacktrace.c
    @@ -102,7 +102,7 @@ __save_stack_trace_reliable(struct stack_trace *trace,
    for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state);
    unwind_next_frame(&state)) {

    - regs = unwind_get_entry_regs(&state);
    + regs = unwind_get_entry_regs(&state, NULL);
    if (regs) {
    /*
    * Kernel mode registers on the stack indicate an
    \
     
     \ /
      Last update: 2017-12-30 18:58    [W:4.061 / U:0.012 seconds]
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