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Date: Sun, 30 Jan 2022 08:29:08 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Marco Elver <elver@...gle.com>
Cc: Baoquan He <bhe@...hat.com>, Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
kexec@...ts.infradead.org, linux-doc@...r.kernel.org,
kasan-dev@...glegroups.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] sched: unset panic_on_warn before calling panic()
On 1/28/22 19:52, Marco Elver wrote:
> On Fri, 28 Jan 2022 at 12:42, Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>>
>> As done in the full WARN() handler, panic_on_warn needs to be cleared
>> before calling panic() to avoid recursive panics.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>> ---
>> kernel/sched/core.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 848eaa0..f5b0886 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -5524,8 +5524,17 @@ static noinline void __schedule_bug(struct task_struct *prev)
>> pr_err("Preemption disabled at:");
>> print_ip_sym(KERN_ERR, preempt_disable_ip);
>> }
>> - if (panic_on_warn)
>> +
>> + if (panic_on_warn) {
>> + /*
>> + * This thread may hit another WARN() in the panic path.
>> + * Resetting this prevents additional WARN() from panicking the
>> + * system on this thread. Other threads are blocked by the
>> + * panic_mutex in panic().
>> + */
>> + panic_on_warn = 0;
>> panic("scheduling while atomic\n");
>
> I agree this is worth fixing.
>
> But: Why can't the "panic_on_warn = 0" just be moved inside panic(),
> instead of copy-pasting this all over the place?
OK, it looks better.
Let me wait for some days, if no more comments, I will send v2
to move "panic_on_warn = 0" inside panic() and remove it from
the other places, like this:
diff --git a/kernel/panic.c b/kernel/panic.c
index 55b50e052ec3..95ba825522dd 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -185,6 +185,16 @@ void panic(const char *fmt, ...)
int old_cpu, this_cpu;
bool _crash_kexec_post_notifiers = crash_kexec_post_notifiers;
+ if (panic_on_warn) {
+ /*
+ * This thread may hit another WARN() in the panic path.
+ * Resetting this prevents additional WARN() from
panicking the
+ * system on this thread. Other threads are blocked by the
+ * panic_mutex in panic().
+ */
+ panic_on_warn = 0;
+ }
+
/*
* Disable local interrupts. This will prevent panic_smp_self_stop
* from deadlocking the first cpu that invokes the panic, since
@@ -576,16 +586,8 @@ void __warn(const char *file, int line, void
*caller, unsigned taint,
if (regs)
show_regs(regs);
- if (panic_on_warn) {
- /*
- * This thread may hit another WARN() in the panic path.
- * Resetting this prevents additional WARN() from
panicking the
- * system on this thread. Other threads are blocked by the
- * panic_mutex in panic().
- */
- panic_on_warn = 0;
+ if (panic_on_warn)
panic("panic_on_warn set ...\n");
- }
if (!regs)
dump_stack();
diff --git a/lib/ubsan.c b/lib/ubsan.c
index bdc380ff5d5c..36bd75e33426 100644
--- a/lib/ubsan.c
+++ b/lib/ubsan.c
@@ -154,16 +154,8 @@ static void ubsan_epilogue(void)
current->in_ubsan--;
- if (panic_on_warn) {
- /*
- * This thread may hit another WARN() in the panic path.
- * Resetting this prevents additional WARN() from
panicking the
- * system on this thread. Other threads are blocked by the
- * panic_mutex in panic().
- */
- panic_on_warn = 0;
+ if (panic_on_warn)
panic("panic_on_warn set ...\n");
- }
}
void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs)
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 3ad9624dcc56..f14146563d41 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -117,16 +117,8 @@ static void end_report(unsigned long *flags,
unsigned long addr)
pr_err("==================================================================\n");
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
spin_unlock_irqrestore(&report_lock, *flags);
- if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT,
&kasan_flags)) {
- /*
- * This thread may hit another WARN() in the panic path.
- * Resetting this prevents additional WARN() from
panicking the
- * system on this thread. Other threads are blocked by the
- * panic_mutex in panic().
- */
- panic_on_warn = 0;
+ if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
panic("panic_on_warn set ...\n");
- }
if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
panic("kasan.fault=panic set ...\n");
kasan_enable_current();
Thanks,
Tiezhu
>
> I may be missing something obvious why this hasn't been done before...
>
> Thanks,
> -- Marco
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