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SubjectRe: [PATCH v3 3/4] kdb: Fix "btc <cpu>" crash if the CPU didn't round up
On Wed, Sep 25, 2019 at 01:02:19PM -0700, Douglas Anderson wrote:
>
> I noticed that when I did "btc <cpu>" and the CPU I passed in hadn't
> rounded up that I'd crash. I was going to copy the same fix from
> commit 162bc7f5afd7 ("kdb: Don't back trace on a cpu that didn't round
> up") into the "not all the CPUs" case, but decided it'd be better to
> clean things up a little bit.
>
> This consolidates the two code paths. It is _slightly_ wasteful in in
> that the checks for "cpu" being too small or being offline isn't
> really needed when we're iterating over all online CPUs, but that
> really shouldn't hurt. Better to have the same code path.
>
> While at it, eliminate at least one slightly ugly (and totally
> needless) recursive use of kdb_parse().
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> Changes in v3:
> - Patch ("kdb: Fix "btc <cpu>" crash if the CPU...") new for v3.
>
> Changes in v2: None
>
> kernel/debug/kdb/kdb_bt.c | 61 ++++++++++++++++++++++-----------------
> 1 file changed, 34 insertions(+), 27 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
> index 120fc686c919..d9af139f9a31 100644
> --- a/kernel/debug/kdb/kdb_bt.c
> +++ b/kernel/debug/kdb/kdb_bt.c
> @@ -101,6 +101,27 @@ kdb_bt1(struct task_struct *p, unsigned long mask, bool btaprompt)
> return 0;
> }
>
> +static void
> +kdb_bt_cpu(unsigned long cpu)
> +{
> + struct task_struct *kdb_tsk;
> +
> + if (cpu >= num_possible_cpus() || !cpu_online(cpu)) {
> + kdb_printf("WARNING: no process for cpu %ld\n", cpu);
> + return;
> + }
> +
> + /* If a CPU failed to round up we could be here */
> + kdb_tsk = KDB_TSK(cpu);
> + if (!kdb_tsk) {
> + kdb_printf("WARNING: no task for cpu %ld\n", cpu);
> + return;
> + }
> +
> + kdb_set_current_task(kdb_tsk);
> + kdb_bt1(kdb_tsk, ~0UL, false);
> +}
> +
> int
> kdb_bt(int argc, const char **argv)
> {
> @@ -161,7 +182,6 @@ kdb_bt(int argc, const char **argv)
> } else if (strcmp(argv[0], "btc") == 0) {
> unsigned long cpu = ~0;
> struct task_struct *save_current_task = kdb_current_task;
> - char buf[80];
> if (argc > 1)
> return KDB_ARGCOUNT;
> if (argc == 1) {
> @@ -169,35 +189,22 @@ kdb_bt(int argc, const char **argv)
> if (diag)
> return diag;
> }
> - /* Recursive use of kdb_parse, do not use argv after
> - * this point */
> - argv = NULL;
> if (cpu != ~0) {
> - if (cpu >= num_possible_cpus() || !cpu_online(cpu)) {
> - kdb_printf("no process for cpu %ld\n", cpu);
> - return 0;
> - }
> - sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
> - kdb_parse(buf);
> - return 0;
> - }
> - kdb_printf("btc: cpu status: ");
> - kdb_parse("cpu\n");
> - for_each_online_cpu(cpu) {
> - void *kdb_tsk = KDB_TSK(cpu);
> -
> - /* If a CPU failed to round up we could be here */
> - if (!kdb_tsk) {
> - kdb_printf("WARNING: no task for cpu %ld\n",
> - cpu);
> - continue;
> + kdb_bt_cpu(cpu);
> + } else {
> + /*
> + * Recursive use of kdb_parse, do not use argv after
> + * this point.
> + */
> + argv = NULL;
> + kdb_printf("btc: cpu status: ");
> + kdb_parse("cpu\n");
> + for_each_online_cpu(cpu) {
> + kdb_bt_cpu(cpu);
> + touch_nmi_watchdog();
> }
> -
> - sprintf(buf, "btt 0x%px\n", kdb_tsk);
> - kdb_parse(buf);
> - touch_nmi_watchdog();
> + kdb_set_current_task(save_current_task);
> }
> - kdb_set_current_task(save_current_task);

Why does this move out into only one of the conditional branches?
Don't both of the above paths modify the current task?


Daniel.


> return 0;
> } else {
> if (argc) {
> --
> 2.23.0.351.gc4317032e6-goog
>

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