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Subject[PATCH v6 4/4] kdb: Don't back trace on a cpu that didn't round up
Date
If you have a CPU that fails to round up and then run 'btc' you'll end
up crashing in kdb becaue we dereferenced NULL. Let's add a check.
It's wise to also set the task to NULL when leaving the debugger so
that if we fail to round up on a later entry into the debugger we
won't backtrace a stale task.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v6: None
Changes in v5: None
Changes in v4:
- Also clear out .debuggerinfo.
- Also clear out .debuggerinfo and .task for the master.
- Remove clearing out in kdb_stub for offline CPUs; it's now redundant.

Changes in v3:
- Don't back trace on a cpu that didn't round up new for v3.

Changes in v2: None

kernel/debug/debug_core.c | 4 ++++
kernel/debug/kdb/kdb_bt.c | 11 ++++++++++-
kernel/debug/kdb/kdb_debugger.c | 7 -------
3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 1fb8b239e567..5cc608de6883 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -592,6 +592,8 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
arch_kgdb_ops.correct_hw_break();
if (trace_on)
tracing_on();
+ kgdb_info[cpu].debuggerinfo = NULL;
+ kgdb_info[cpu].task = NULL;
kgdb_info[cpu].exception_state &=
~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
kgdb_info[cpu].enter_kgdb--;
@@ -724,6 +726,8 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
if (trace_on)
tracing_on();

+ kgdb_info[cpu].debuggerinfo = NULL;
+ kgdb_info[cpu].task = NULL;
kgdb_info[cpu].exception_state &=
~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
kgdb_info[cpu].enter_kgdb--;
diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
index 7921ae4fca8d..7e2379aa0a1e 100644
--- a/kernel/debug/kdb/kdb_bt.c
+++ b/kernel/debug/kdb/kdb_bt.c
@@ -186,7 +186,16 @@ kdb_bt(int argc, const char **argv)
kdb_printf("btc: cpu status: ");
kdb_parse("cpu\n");
for_each_online_cpu(cpu) {
- sprintf(buf, "btt 0x%px\n", KDB_TSK(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;
+ }
+
+ sprintf(buf, "btt 0x%px\n", kdb_tsk);
kdb_parse(buf);
touch_nmi_watchdog();
}
diff --git a/kernel/debug/kdb/kdb_debugger.c b/kernel/debug/kdb/kdb_debugger.c
index 15e1a7af5dd0..53a0df6e4d92 100644
--- a/kernel/debug/kdb/kdb_debugger.c
+++ b/kernel/debug/kdb/kdb_debugger.c
@@ -118,13 +118,6 @@ int kdb_stub(struct kgdb_state *ks)
kdb_bp_remove();
KDB_STATE_CLEAR(DOING_SS);
KDB_STATE_SET(PAGER);
- /* zero out any offline cpu data */
- for_each_present_cpu(i) {
- if (!cpu_online(i)) {
- kgdb_info[i].debuggerinfo = NULL;
- kgdb_info[i].task = NULL;
- }
- }
if (ks->err_code == DIE_OOPS || reason == KDB_REASON_OOPS) {
ks->pass_exception = 1;
KDB_FLAG_SET(CATASTROPHIC);
--
2.20.0.rc0.387.gc7a69e6b6c-goog
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