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Groups > linux.kernel > #1320093
| From | Peter Hurley <peter@hurleysoftware.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code |
| Date | 2016-01-27 23:50 +0100 |
| Message-ID | <qVH4u-2ek-9@gated-at.bofh.it> (permalink) |
| References | <qVx58-3fC-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 01/27/2016 04:01 AM, Byungchul Park wrote:
> changes form v3 to v4
> - reuse a existing code as much as possible for preventing an infinite
> recursive cycle.
>
> changes from v2 to v3
> - avoid printk() only in case of lockup suspected, not real lockup in
> which case it does not help at all.
> - consider not only console_sem.lock but also logbuf_lock which is used
> by printk().
>
> changes from v1 to v2
> - only change comment and commit message esp. replacing "deadlock" with
> "infinite recursive cycle", since it is not an actual deadlock.
>
> thanks,
> byungchul
>
> -----8<-----
> From 7b0c6e48625632fa1732b619083dc550b5d924c6 Mon Sep 17 00:00:00 2001
> From: Byungchul Park <byungchul.park@lge.com>
> Date: Wed, 27 Jan 2016 18:11:55 +0900
> Subject: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the
> debug code
>
> It causes an infinite recursive cycle when using CONFIG_DEBUG_SPINLOCK,
> in the spin_dump(). Backtrace prints printk() -> console_trylock() ->
> do_raw_spin_lock() -> spin_dump() -> printk()... infinitely.
printk() is potentially recursive in many situations.
What about spinlocks used by console drivers?
And we already have lockdep turned off to avoid triggering a recursive
lockdep report (which I think is a mistake).
I think we should be working toward properly handling recursion
in printk().
Regards,
Peter Hurley
> When the debug spinlock code is called from printk(), we should prevent
> calling spin_dump() and the like, calling printk() again in that context.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
> include/linux/debug_locks.h | 4 ++++
> kernel/locking/spinlock_debug.c | 14 +++++++++++---
> 2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/debug_locks.h b/include/linux/debug_locks.h
> index 822c135..b0f977e 100644
> --- a/include/linux/debug_locks.h
> +++ b/include/linux/debug_locks.h
> @@ -10,6 +10,10 @@ struct task_struct;
> extern int debug_locks;
> extern int debug_locks_silent;
>
> +static inline void __debug_locks_on(void)
> +{
> + debug_locks = 1;
> +}
>
> static inline int __debug_locks_off(void)
> {
> diff --git a/kernel/locking/spinlock_debug.c b/kernel/locking/spinlock_debug.c
> index 0374a59..65177ba 100644
> --- a/kernel/locking/spinlock_debug.c
> +++ b/kernel/locking/spinlock_debug.c
> @@ -113,11 +113,19 @@ static void __spin_lock_debug(raw_spinlock_t *lock)
> return;
> __delay(1);
> }
> - /* lockup suspected: */
> - spin_dump(lock, "lockup suspected");
> +
> + /*
> + * We should prevent calling printk() further, since it would cause
> + * an infinite recursive cycle if it's called from printk()!
> + */
> + if (__debug_locks_off()) {
> + /* lockup suspected: */
> + spin_dump(lock, "lockup suspected");
> #ifdef CONFIG_SMP
> - trigger_all_cpu_backtrace();
> + trigger_all_cpu_backtrace();
> #endif
> + __debug_locks_on();
> + }
>
> /*
> * The trylock above was causing a livelock. Give the lower level arch
>
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[PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-27 13:10 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Peter Hurley <peter@hurleysoftware.com> - 2016-01-27 23:50 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-28 08:20 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 09:20 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-28 03:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-28 03:40 +0100
RE: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code "byungchul.park" <byungchul.park@lge.com> - 2016-01-28 06:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-28 07:10 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-28 09:30 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-28 11:50 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-28 12:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-01-28 16:50 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Peter Hurley <peter@hurleysoftware.com> - 2016-01-29 00:10 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 01:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 02:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 04:10 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 05:10 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 13:20 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 01:30 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Peter Hurley <peter@hurleysoftware.com> - 2016-01-29 05:40 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 06:30 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Peter Hurley <peter@hurleysoftware.com> - 2016-01-29 06:50 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 07:20 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 07:40 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-31 13:30 +0100
[PATCH 2/3] printk: introduce reset_console_drivers() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-31 13:40 +0100
Re: [PATCH 2/3] printk: introduce reset_console_drivers() kbuild test robot <lkp@intel.com> - 2016-01-31 13:50 +0100
[PATCH 1/3] printk: introduce console_reset_on_panic() function Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-31 13:40 +0100
[PATCH 3/3] spinlock_debug: panic on recursive lock spin_dump() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-31 13:40 +0100
Re: [PATCH 3/3] spinlock_debug: panic on recursive lock spin_dump() Sergey Senozhatsky <sergey.senozhatsky@gmail.com> - 2016-02-01 17:20 +0100
Re: [PATCH 3/3] spinlock_debug: panic on recursive lock spin_dump() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-02-02 09:00 +0100
Re: [PATCH 1/3] printk: introduce console_reset_on_panic() function kbuild test robot <lkp@intel.com> - 2016-01-31 13:50 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 08:00 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-01-29 08:20 +0100
Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park <byungchul.park@lge.com> - 2016-01-29 09:20 +0100
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