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exit: Move preemption fixup up, move blocking operations down 

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: 1dc0fffc48 ("sched/core: Robustify preemption leak checks")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200305220657.46800-1-jannh@google.com
This commit is contained in:
Jann Horn 2020-03-05 23:06:57 +01:00 committed by Peter Zijlstra
parent 64297f2b03
commit 586b58cac8
1 changed files with 16 additions and 9 deletions
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25
kernel/exit.c
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@ -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);