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Subject[PATCH v2] exit: Move preemption fixup up, move blocking operations down
From
With CONFIG_DEBUG_ATOMIC_SLEEP=y and CONFIG_CGROUPS=y, kernel oopses in
non-preemptible context look untidy; after the main oops, the kernel prints
a "sleeping function called from invalid context" report because
exit_signals() -> cgroup_threadgroup_change_begin() -> percpu_down_read()
can sleep, and that happens before the preempt_count_set(PREEMPT_ENABLED)
fixup.

It looks like the same thing applies to profile_task_exit() and
kcov_task_exit().

Fix it by moving the preemption fixup up and the calls to
profile_task_exit() and kcov_task_exit() down.

Fixes: 1dc0fffc48af ("sched/core: Robustify preemption leak checks")
Signed-off-by: Jann Horn <jannh@google.com>
---
As so often, I have no idea which tree this should go through. tip? mm?

v2: now without adding redundant whitespace...

kernel/exit.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 2833ffb0c211..eb42d49fd99d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -713,8 +713,12 @@ void __noreturn do_exit(long code)
struct task_struct *tsk = current;
int group_dead;

- profile_task_exit(tsk);
- kcov_task_exit(tsk);
+ /*
+ * We can get here from a kernel oops, sometimes with preemption off.
+ * Start by checking for critical errors.
+ * Then fix up important state like USER_DS and preemption.
+ * Then do everything else.
+ */

WARN_ON(blk_needs_flush_plug(tsk));

@@ -732,6 +736,16 @@ void __noreturn do_exit(long code)
*/
set_fs(USER_DS);

+ if (unlikely(in_atomic())) {
+ pr_info("note: %s[%d] exited with preempt_count %d\n",
+ current->comm, task_pid_nr(current),
+ preempt_count());
+ preempt_count_set(PREEMPT_ENABLED);
+ }
+
+ profile_task_exit(tsk);
+ kcov_task_exit(tsk);
+
ptrace_event(PTRACE_EVENT_EXIT, code);

validate_creds_for_do_exit(tsk);
@@ -749,13 +763,6 @@ void __noreturn do_exit(long code)

exit_signals(tsk); /* sets PF_EXITING */

- if (unlikely(in_atomic())) {
- pr_info("note: %s[%d] exited with preempt_count %d\n",
- current->comm, task_pid_nr(current),
- preempt_count());
- preempt_count_set(PREEMPT_ENABLED);
- }
-
/* sync mm's RSS info before statistics gathering */
if (tsk->mm)
sync_mm_rss(tsk->mm);
base-commit: 9f65ed5fe41ce08ed1cb1f6a950f9ec694c142ad
--
2.25.0.265.gbab2e86ba0-goog

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