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Date: Thu, 5 Mar 2020 22:59:53 +0100 From: Jann Horn <jannh@...gle.com> To: Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Frederic Weisbecker <fweisbec@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org Subject: [PATCH] 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: 1dc0fffc48af ("sched/core: Robustify preemption leak checks") Signed-off-by: Jann Horn <jannh@...gle.com> --- As so often, I have no idea which tree this should go through. tip? mm? kernel/exit.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 2833ffb0c211..db77c540aa92 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 +736,17 @@ 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 +764,6 @@ 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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