BUG: scheduling while atomic

"Scheduling while atomic" means that a thread has called schedule() during an operation which is supposed to be atomic (ie uninterrupted).

printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",  prev->comm, prev->pid, preempt_count());

ex.

spin_lock_irqsave(&sysLock, flags);

msleep(100);

spin_lock_irqsave -> preempt_disable -> inc_preempt_count [current_thread_info()->preempt_count = 1 ]

msleep -> schedule -> preempt_disable -> inc_preempt_count [current_thread_info()->preempt_count = 2 ]

msleep -> schedule -> schedule_debug -> in_atomic_preempt_off

[ in_atomic_preempt_off checks if (preempt_count != 1) then printk "BUG: scheduling while atomic" ]

kernel module memory (leaking) detector

搭配kallsyms_lookup,我們除了可以抓出function name之外,還可以抓出module name,所以我把kallsyms_lookup埋在kmalloc呼叫中,但是,kmalloc被定義為inline function,所以不可能從__builtin_return_address拉出caller address,必需把kmalloc改為非inline function,所以我把kmalloc拉到slab.c,並加入以下幾行


/*inline*/ void *kmalloc(size_t size, gfp_t flags) 
{ 
char *modname=NULL;
const char *name=NULL;
unsigned long kaoffset, kasize;
char namebuf[KSYM_NAME_LEN];
 
unsigned long caller = (unsigned long) __builtin_return_address(0);
name = kallsyms_lookup(caller, &kasize, &kaoffset, &modname, namebuf);
if (modname) 
{ 
printk("modname %s\n",modname);
addElement(modname,size,0);
}

addElement是我們自己寫的函式,主要是在收集由kmalloc攔截到的資訊,有興趣的朋友可以自己寫自己的hook function

在kfree function內也擺上hook function,大概如下,記得要把obj_size-20,因為kmalloc會多佔20bytes空間於memory heap


void kfree(const void *objp) 
{ 
struct kmem_cache *c;
unsigned long flags;
//hack
char *modname=NULL;
const char *name=NULL;
unsigned long kaoffset, kasize;
char namebuf[KSYM_NAME_LEN];
 
 
if (unlikely(ZERO_OR_NULL_PTR(objp))) 
return;
local_irq_save(flags);
kfree_debugcheck(objp);
c = virt_to_cache(objp);
//hack
unsigned long caller = (unsigned long) __builtin_return_address(0);
name = kallsyms_lookup(caller, &kasize, &kaoffset, &modname, namebuf);
if (modname) 
{ 
printk("modname %s\n",modname);
addElement(modname,0,obj_size(c)-20);
} 
//hack end
debug_check_no_locks_freed(objp, obj_size(c));
debug_check_no_obj_freed(objp, obj_size(c));
__cache_free(c, (void *)objp);
local_irq_restore(flags);
}

轉貼 http://daydreamer.idv.tw/rewrite.php/read-55.html