[PATCH AUTOSEL 5.7 144/274] exit: Move preemption fixup up, move blocking operations down

From: Sasha Levin
Date: Mon Jun 08 2020 - 19:10:36 EST


From: Jann Horn <jannh@xxxxxxxxxx>

[ Upstream commit 586b58cac8b4683eb58a1446fbc399de18974e40 ]

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200305220657.46800-1-jannh@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/exit.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index ce2a75bc0ade..d56fe51bdf07 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -708,8 +708,12 @@ 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));

@@ -727,6 +731,16 @@ 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);
@@ -744,13 +758,6 @@ 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);
--
2.25.1