Re: [PATCH resend] slub: Add back check for free nonslab objects

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2021/9/28 23:43, Matthew Wilcox wrote:
> On Mon, Sep 27, 2021 at 03:53:47PM +0800, Kefeng Wang wrote:
>> On 2021/9/27 15:22, Vlastimil Babka wrote:
>>> On 9/27/21 04:15, Kefeng Wang wrote:
>>>> After commit ("f227f0faf63b slub: fix unreclaimable slab stat for bulk
>>>> free"), the check for free nonslab page is replaced by VM_BUG_ON_PAGE,
>>>> which only check with CONFIG_DEBUG_VM enabled, but this config may
>>>> impact performance, so it only for debug.
>>>>
>>>> Commit ("0937502af7c9 slub: Add check for kfree() of non slab objects.")
>>>> add the ability, which should be needed in any configs to catch the
>>>> invalid free, they even could be potential issue, eg, memory corruption,
>>>> use after free and double-free, so replace VM_BUG_ON_PAGE to WARN_ON, and
>>>> add dump_page() to help use to debug the issue.
>>> There are other situations in SLUB (such as with smaller allocations that
>>> don't go directly to page allocator) where use after free and double-free
>>> are undetected in non-debug configs, and it's expected that anyone debugging
>>> them will enable slub_debug or even DEBUG_VM. Why should this special case
>>> with nonslab pages be different?
>>
>> I want the check back in kfree, this one is used  widely in driver, and the
>> probability
>>
>> of problem occurred is bigger in driver, especially in some out of tree
>> drivers.
> 
> Why would we want to improve life for out of tree drivers?  Drivers should
> be in-tree.  That's been the Linux Way for thirty years.
> 
> I remain sceptical that dump_page() is actually useful for debugging
> drivers anyway.  dump_stack(), I could see -- that'll tell you which
> driver called kfree() on a bogus pointer.  But how does dump_page() help?
Add dump_page here because it could help us debug for memory corruption,
if we think it is redundant, I could drop it in the next version.
> .
>