lkml.org 
[lkml]   [2018]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4 v6] lib: debugobjects: add global free list and the counter
On Tue, 6 Feb 2018, Yang Shi wrote:
> + /*
> + * Reuse objs from the global free list, they will be reinitialized
> + * when allocating
> + */
> + while (obj_nr_tofree > 0 && (obj_pool_free < obj_pool_min_free)) {
> + raw_spin_lock_irqsave(&pool_lock, flags);
> + obj = hlist_entry(obj_to_free.first, typeof(*obj), node);

This is racy vs. the worker thread. Assume obj_nr_tofree = 1:

CPU0 CPU1
worker
lock(&pool_lock); while (obj_nr_tofree > 0 && ...) {
obj = hlist_entry(obj_to_free); lock(&pool_lock);
hlist_del(obj);
obj_nr_tofree--;
...
unlock(&pool_lock);
obj = hlist_entry(obj_to_free);
hlist_del(obj); <------- NULL pointer dereference

Not what you want, right? The counter or the list head need to be rechecked
after the lock is acquired.

> + hlist_del(&obj->node);
> + obj_nr_tofree--;
> + hlist_add_head(&obj->node, &obj_pool);
> + obj_pool_free++;
> + raw_spin_unlock_irqrestore(&pool_lock, flags);
> + }

Thanks,

tglx

\
 
 \ /
  Last update: 2018-02-12 17:26    [W:0.127 / U:4.708 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site