Andy Whitcroft wrote:
> 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
>
This is definatly clearing up a bunch of problems with the current -mm.
-apw
-
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