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

[Jinjiang Tu <tujinjiang@huawei.com>]

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.