On Tue, 8 Sep 2015, Joseph Qi wrote:
> Hi Julia,
>
> On 2015/9/7 22:01, Julia Lawall wrote:
> > It looks like a serious problem, because the loop update does a
> > dereference of the first argument of list_for_each via list_entry.
> >
> Could you give more details about this? IMO, it doesn't make any
> difference in functional logic.
Do you expect that setting lock to NULL will cause a break out of the
loop? Because it does not. The expansion of list_for_each_entry is:
#define list_for_each_entry(pos, head, member) \
for (pos = list_first_entry(head, typeof(*pos), member); \
&pos->member != (head); \
pos = list_next_entry(pos, member))
Since pos is NULL, &pos->member != (head), so we will take the loop
update. List_next_entry is:
#define list_next_entry(pos, member) \
list_entry((pos)->member.next, typeof(*(pos)), member)
list_entry is container_of, which does
const typeof( ((type *)0)->member ) *__mptr = (ptr);
This causes (pos)->member.next to be evaluated, which since pos is NULL
will crash.
julia
>
> > julia
> >
> > On Mon, 7 Sep 2015, kbuild test robot wrote:
> >
> >> TO: Joseph Qi <joseph.qi@xxxxxxxxxx>
> >> CC: kbuild-all@xxxxxx
> >> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >> CC: Linux Memory Management List <linux-mm@xxxxxxxxx>
> >>
> >> tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> >> head: 7d9071a095023cd1db8fa18fa0d648dc1a5210e0
> >> commit: f83c7b5e9fd633fe91128af116e6472a8c4d29a5 ocfs2/dlm: use list_for_each_entry instead of list_for_each
> >> date: 3 days ago
> >> :::::: branch date: 33 hours ago
> >> :::::: commit date: 3 days ago
> >>
> >>>> fs/ocfs2/dlm/dlmrecovery.c:1824:4-23: iterator with update on line 1827
> >>
> >> git remote add linus git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >> git remote update linus
> >> git checkout f83c7b5e9fd633fe91128af116e6472a8c4d29a5
> >> vim +1824 fs/ocfs2/dlm/dlmrecovery.c
> >>
> >> 6714d8e8 Kurt Hackel 2005-12-15 1818 BUG_ON(!(mres->flags & DLM_MRES_MIGRATION));
> >> 6714d8e8 Kurt Hackel 2005-12-15 1819
> >> 34aa8dac Junxiao Bi 2014-04-03 1820 lock = NULL;
> >> 6714d8e8 Kurt Hackel 2005-12-15 1821 spin_lock(&res->spinlock);
> >> e17e75ec Kurt Hackel 2007-01-05 1822 for (j = DLM_GRANTED_LIST; j <= DLM_BLOCKED_LIST; j++) {
> >> e17e75ec Kurt Hackel 2007-01-05 1823 tmpq = dlm_list_idx_to_ptr(res, j);
> >> f83c7b5e Joseph Qi 2015-09-04 @1824 list_for_each_entry(lock, tmpq, list) {
> >> 34aa8dac Junxiao Bi 2014-04-03 1825 if (lock->ml.cookie == ml->cookie)
> >> 6714d8e8 Kurt Hackel 2005-12-15 1826 break;
> >> 34aa8dac Junxiao Bi 2014-04-03 @1827 lock = NULL;
> >> 6714d8e8 Kurt Hackel 2005-12-15 1828 }
> >> e17e75ec Kurt Hackel 2007-01-05 1829 if (lock)
> >> e17e75ec Kurt Hackel 2007-01-05 1830 break;
> >>
> >> ---
> >> 0-DAY kernel test infrastructure Open Source Technology Center
> >> https://lists.01.org/pipermail/kbuild-all Intel Corporation
> >>
> >
> > .
> >
>
>
>
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