Ingo Molnar wrote:
> * Randy.Dunlap <[email protected]> wrote:
>
>
>>BUG: unable to handle kernel paging request at virtual address 22222232
>
>
> ok, this was a big thinko on my part, and it was right before our eyes.
> Mutex deadlock checking relied on the 'big mutex debugging lock', but
> that one is gone now - so mutex deadlock checking became racy (as your
> crashes nicely pinpointed that). The races are more likely with an
> increasing number of CPUs.
>
> so the patch below finishes the cleanup i started: it removes deadlock
> checking from the mutex code and lets the lock validator do that. This
> should also be (much) faster on SMP, because the lock validator is
> lockless in the fastpath. (if CONFIG_DEBUG_LOCKDEP is disabled)
>
> Ingo
>
> ----------------
> Subject: better lock debugging: remove mutex deadlock checking code
> From: Ingo Molnar <[email protected]>
>
> with the lock validator we detect mutex deadlocks (and more), the mutex
> deadlock checking code is both redundant and slower. So remove it.
>
> Signed-off-by: Ingo Molnar <[email protected]>
> ---
> kernel/mutex-debug.c | 126 ---------------------------------------------------
> lib/Kconfig.debug | 8 ---
> 2 files changed, 1 insertion(+), 133 deletions(-)
>
> Index: linux/kernel/mutex-debug.c
> ===================================================================
> --- linux.orig/kernel/mutex-debug.c
> +++ linux/kernel/mutex-debug.c
> @@ -23,128 +23,6 @@
>
> #include "mutex-debug.h"
>
> -static void printk_task(struct task_struct *p)
> -{
> - if (p)
> - printk("%16s:%5d [%p, %3d]", p->comm, p->pid, p, p->prio);
> - else
> - printk("<none>");
> -}
> -
> -static void printk_ti(struct thread_info *ti)
> -{
> - if (ti)
> - printk_task(ti->task);
> - else
> - printk("<none>");
> -}
> -
> -static void printk_lock(struct mutex *lock, int print_owner)
> -{
> -#ifdef CONFIG_PROVE_MUTEX_LOCKING
> - printk(" [%p] {%s}\n", lock, lock->dep_map.name);
> -#else
> - printk(" [%p]\n", lock);
> -#endif
> -
> - if (print_owner && lock->owner) {
> - printk(".. held by: ");
> - printk_ti(lock->owner);
> - printk("\n");
> - }
> -}
> -
> -static void report_deadlock(struct task_struct *task, struct mutex *lock,
> - struct mutex *lockblk)
> -{
> - printk("\n%s/%d is trying to acquire this lock:\n",
> - current->comm, current->pid);
> - printk_lock(lock, 1);
> - debug_show_held_locks(current);
> -
> - if (lockblk) {
> - printk("but %s/%d is deadlocking current task %s/%d!\n\n",
> - task->comm, task->pid, current->comm, current->pid);
> - printk("\n%s/%d is blocked on this lock:\n",
> - task->comm, task->pid);
> - printk_lock(lockblk, 1);
> -
> - debug_show_held_locks(task);
> -
> - printk("\n%s/%d's [blocked] stackdump:\n\n",
> - task->comm, task->pid);
> - show_stack(task, NULL);
> - }
> -
> - printk("\n%s/%d's [current] stackdump:\n\n",
> - current->comm, current->pid);
> - dump_stack();
> - debug_show_all_locks();
> - printk("[ turning off deadlock detection. Please report this. ]\n\n");
> - local_irq_disable();
> -}
> -
> -/*
> - * Recursively check for mutex deadlocks:
> - */
> -static int check_deadlock(struct mutex *lock, int depth, struct thread_info *ti)
> -{
> - struct mutex *lockblk;
> - struct task_struct *task;
> -
> - if (!debug_locks)
> - return 0;
> -
> - ti = lock->owner;
> - if (!ti)
> - return 0;
> -
> - task = ti->task;
> - /*
> - * In the PROVE_MUTEX_LOCKING we are tracking all held
> - * locks already, which allows us to optimize this:
> - */
> -#ifdef CONFIG_PROVE_MUTEX_LOCKING
> - if (!task->lockdep_depth)
> - return 0;
> -#endif
> - lockblk = NULL;
> - if (task->blocked_on)
> - lockblk = task->blocked_on->lock;
> -
> - /* Self-deadlock: */
> - if (current == task) {
> - debug_locks_off();
> - if (depth)
> - return 1;
> - printk("\n==========================================\n");
> - printk( "[ BUG: lock recursion deadlock detected! |\n");
> - printk( "------------------------------------------\n");
> - report_deadlock(task, lock, NULL);
> - return 0;
> - }
> -
> - /* Ugh, something corrupted the lock data structure? */
> - if (depth > 20) {
> - debug_locks_off();
> - printk("\n===========================================\n");
> - printk( "[ BUG: infinite lock dependency detected!? |\n");
> - printk( "-------------------------------------------\n");
> - report_deadlock(task, lock, lockblk);
> - return 0;
> - }
> -
> - /* Recursively check for dependencies: */
> - if (lockblk && check_deadlock(lockblk, depth+1, ti)) {
> - printk("\n============================================\n");
> - printk( "[ BUG: circular locking deadlock detected! ]\n");
> - printk( "--------------------------------------------\n");
> - report_deadlock(task, lock, lockblk);
> - return 0;
> - }
> - return 0;
> -}
> -
> /*
> * Must be called with lock->wait_lock held.
> */
> @@ -178,9 +56,7 @@ void debug_mutex_add_waiter(struct mutex
> struct thread_info *ti)
> {
> SMP_DEBUG_WARN_ON(!spin_is_locked(&lock->wait_lock));
> -#ifdef CONFIG_DEBUG_MUTEX_DEADLOCKS
> - check_deadlock(lock, 0, ti);
> -#endif
> +
> /* Mark the current thread as blocked on the lock: */
> ti->task->blocked_on = waiter;
> waiter->lock = lock;
> Index: linux/lib/Kconfig.debug
> ===================================================================
> --- linux.orig/lib/Kconfig.debug
> +++ linux/lib/Kconfig.debug
> @@ -164,14 +164,6 @@ config DEBUG_MUTEX_ALLOC
> (kfree(), kmem_cache_free(), free_pages(), vfree(), etc.),
> or whether there is any lock held during task exit.
>
> -config DEBUG_MUTEX_DEADLOCKS
> - bool "Detect mutex related deadlocks"
> - default y
> - depends on DEBUG_MUTEXES
> - help
> - This feature will automatically detect and report mutex related
> - deadlocks, as they happen.
> -
> config DEBUG_RT_MUTEXES
> bool "RT Mutex debugging, deadlock detection"
> default y
I'll shove this one in for testing too. Results on TKO as I have them.
-apw
-
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