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Subject[PATCH 4/5] kdb: Gid rid of implicit setting of the current task / regs
Date
Some (but not all?) of the kdb backtrace paths would cause the
kdb_current_task and kdb_current_regs to remain changed. As discussed
in a review of a previous patch [1], this doesn't seem intuitive, so
let's fix that.

...but, it turns out that there's actually no longer any reason to set
the current task / current regs while backtracing anymore anyway. As
of commit 2277b492582d ("kdb: Fix stack crawling on 'running' CPUs
that aren't the master") if we're backtracing on a task running on a
CPU we ask that CPU to do the backtrace itself. Linux can do that
without anything fancy. If we're doing backtrace on a sleeping task
we can also do that fine without updating globals. So this patch
mostly just turns into deleting a bunch of code.

[1] https://lore.kernel.org/r/20191010150735.dhrj3pbjgmjrdpwr@holly.lan

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

kernel/debug/kdb/kdb_bt.c | 8 +-------
kernel/debug/kdb/kdb_main.c | 2 +-
kernel/debug/kdb/kdb_private.h | 1 -
3 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
index 4af48ac53625..3de0cc780c16 100644
--- a/kernel/debug/kdb/kdb_bt.c
+++ b/kernel/debug/kdb/kdb_bt.c
@@ -119,7 +119,6 @@ kdb_bt_cpu(unsigned long cpu)
return;
}

- kdb_set_current_task(kdb_tsk);
kdb_bt1(kdb_tsk, ~0UL, false);
}

@@ -166,10 +165,8 @@ kdb_bt(int argc, const char **argv)
if (diag)
return diag;
p = find_task_by_pid_ns(pid, &init_pid_ns);
- if (p) {
- kdb_set_current_task(p);
+ if (p)
return kdb_bt1(p, ~0UL, false);
- }
kdb_printf("No process with pid == %ld found\n", pid);
return 0;
} else if (strcmp(argv[0], "btt") == 0) {
@@ -178,11 +175,9 @@ kdb_bt(int argc, const char **argv)
diag = kdbgetularg((char *)argv[1], &addr);
if (diag)
return diag;
- kdb_set_current_task((struct task_struct *)addr);
return kdb_bt1((struct task_struct *)addr, ~0UL, false);
} else if (strcmp(argv[0], "btc") == 0) {
unsigned long cpu = ~0;
- struct task_struct *save_current_task = kdb_current_task;
if (argc > 1)
return KDB_ARGCOUNT;
if (argc == 1) {
@@ -204,7 +199,6 @@ kdb_bt(int argc, const char **argv)
kdb_bt_cpu(cpu);
touch_nmi_watchdog();
}
- kdb_set_current_task(save_current_task);
}
return 0;
} else {
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 4d44b3746836..ba12e9f4661e 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1138,7 +1138,7 @@ static void kdb_dumpregs(struct pt_regs *regs)
console_loglevel = old_lvl;
}

-void kdb_set_current_task(struct task_struct *p)
+static void kdb_set_current_task(struct task_struct *p)
{
kdb_current_task = p;

diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index e829b22f3946..2e296e4a234c 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -240,7 +240,6 @@ extern void *debug_kmalloc(size_t size, gfp_t flags);
extern void debug_kfree(void *);
extern void debug_kusage(void);

-extern void kdb_set_current_task(struct task_struct *);
extern struct task_struct *kdb_current_task;
extern struct pt_regs *kdb_current_regs;

--
2.24.0.432.g9d3f5f5b63-goog
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