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SubjectRe: [PATCH v7 6/7] mm/madvise: employ mmget_still_valid for write lock
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On 3/6/20 2:03 PM, Oleksandr Natalenko wrote:
> Hello.
>
> On Fri, Mar 06, 2020 at 01:52:07PM +0100, Vlastimil Babka wrote:
>> > diff --git a/mm/madvise.c b/mm/madvise.c
>> > index e794367f681e..e77c6c1fad34 100644
>> > --- a/mm/madvise.c
>> > +++ b/mm/madvise.c
>> > @@ -1118,6 +1118,8 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
>> > if (write) {
>> > if (down_write_killable(&mm->mmap_sem))
>> > return -EINTR;
>> > + if (current->mm != mm && !mmget_still_valid(mm))
>> > + goto skip_mm;
>>
>> This will return 0, is that correct? Shoudln't there be a similar error e.g. as
>> when finding the task by pid fails (-ESRCH ?), because IIUC the task here is
>> going away and dumping the core?
>
> Yeah.
>
> Something like this then:
>
> ===
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 48d1da08c160..7ed2f4d13924 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1122,6 +1122,10 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> if (write) {
> if (down_write_killable(&mm->mmap_sem))
> return -EINTR;
> + if (current->mm != mm && !mmget_still_valid(mm)) {
> + error = -ESRCH;
> + goto skip_mm;
> + }
> } else {
> down_read(&mm->mmap_sem);
> }
> @@ -1173,6 +1177,7 @@ int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
> }
> out:
> blk_finish_plug(&plug);
> +skip_mm:
> if (write)
> up_write(&mm->mmap_sem);
> else
>
> ===
>
> ?

Yep, thanks.

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