Messages in this thread Patch in this message | | | From | Byungchul Park <> | Subject | [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code | Date | Wed, 27 Jan 2016 21:01:01 +0900 |
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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.
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 -- 1.9.1
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