Re: [PATCH] mm/slub: Fix incorrect checkings of s->offset

[Waiman Long <longman@redhat.com>]

On 4/27/20 9:18 AM, Waiman Long wrote:
> On 4/27/20 8:38 AM, Matthew Wilcox wrote:
>> On Sun, Apr 26, 2020 at 10:02:12PM -0400, Waiman Long wrote:
>>> In a couple of places in the slub memory allocator, the code uses
>>> "s->offset" as a check to see if the free pointer is put right after 
>>> the
>>> object. That check is no longer true with commit 3202fa62fb43 ("slub:
>>> relocate freelist pointer to middle of object").
>>>
>>> As a result, echoing "1" into the validate sysfs file, e.g. of dentry,
>>> may cause a bunch of "Freepointer corrupt" error reports to appear with
>>> the system in panic afterwards.
>>>
>>> To fix it, use the check "s->offset == s->inuse" instead.
>> I think a little refactoring would make this more clear.
>>
>> unsigned int track_offset(const struct kmem_cache *s)
>> {
>>     return s->inuse + (s->offset == s->inuse) ? sizeof(void *) : 0;
>> }
>
> Yes, that was what I am thinking of doing in v2. 

BTW, "+" has a higher priority than "?:". So we need a parenthesis 
around "?:".

Cheers,
Longman