Re: [PATCH v2 1/2] mm/ksm: fix ksm exec support for prctl

[David Hildenbrand <david@redhat.com>]

On 25.03.24 03:24, Jinjiang Tu wrote:
> 
> 在 2024/3/22 17:02, David Hildenbrand 写道:
>> On 22.03.24 07:09, Jinjiang Tu wrote:
>>> commit 3c6f33b7273a ("mm/ksm: support fork/exec for prctl") inherits
>>> MMF_VM_MERGE_ANY flag when a task calls execve(). Howerver, it doesn't
>>> create the mm_slot, so ksmd will not try to scan this task.
>>>
>>> To fix it, allocate and add the mm_slot to ksm_mm_head in
>>> __bprm_mm_init()
>>> when the mm has MMF_VM_MERGE_ANY flag.
>>>
>>> Fixes: 3c6f33b7273a ("mm/ksm: support fork/exec for prctl")
>>> Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
>>> ---
>>>    fs/exec.c           | 10 ++++++++++
>>>    include/linux/ksm.h | 13 +++++++++++++
>>>    2 files changed, 23 insertions(+)
>>>
>>> diff --git a/fs/exec.c b/fs/exec.c
>>> index ff6f26671cfc..66202d016a0a 100644
>>> --- a/fs/exec.c
>>> +++ b/fs/exec.c
>>> @@ -67,6 +67,7 @@
>>>    #include <linux/time_namespace.h>
>>>    #include <linux/user_events.h>
>>>    #include <linux/rseq.h>
>>> +#include <linux/ksm.h>
>>>      #include <linux/uaccess.h>
>>>    #include <asm/mmu_context.h>
>>> @@ -267,6 +268,13 @@ static int __bprm_mm_init(struct linux_binprm
>>> *bprm)
>>>            goto err_free;
>>>        }
>>>    +    /*
>>> +     * Need to be called with mmap write lock
>>> +     * held, to avoid race with ksmd.
>>> +    */
>>> +    if (ksm_execve(mm))
>>> +        goto err_ksm;
>>> +
>>
>> But now, would we revert what insert_vm_struct() did?
>>
>> We're freeing the VMA later, but we might have accounted memory.
>>
>>
>> What would be cleaner is doing the ksm_execve() before the
>> insert_vm_struct(), and then cleaning up in case insert_vm_struct()
>> failed.
> In fact, ksm_execve() has been called before the insert_vm_struct() in
> this patch.
> 

Ahh, I missed that. Indeed, that works then.

-- 
Cheers,

David / dhildenb