On Sat, 4 Jun 2016 16:19:19 +0900 Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
> Since commit 36324a990cf578b5 ("oom: clear TIF_MEMDIE after oom_reaper
> managed to unmap the address space") changed to use find_lock_task_mm()
> for finding a mm_struct to reap, it is guaranteed that mm->mm_users > 0
> because find_lock_task_mm() returns a task_struct with ->mm != NULL.
> Therefore, we can safely use atomic_inc().
>
> ...
>
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -474,13 +474,8 @@ static bool __oom_reap_task(struct task_struct *tsk)
> p = find_lock_task_mm(tsk);
> if (!p)
> goto unlock_oom;
> -
> mm = p->mm;
> - if (!atomic_inc_not_zero(&mm->mm_users)) {
> - task_unlock(p);
> - goto unlock_oom;
> - }
> -
> + atomic_inc(&mm->mm_users);
> task_unlock(p);
>
> if (!down_read_trylock(&mm->mmap_sem)) {
In an off-list email (please don't do that!) you asked me to replace
mmoom_reaper-dont-call-mmput_async-without-atomic_inc_not_zero.patch
with this above patch.
But the
mmoom_reaper-dont-call-mmput_async-without-atomic_inc_not_zero.patch
changelog is pretty crappy:
: Commit e2fe14564d3316d1 ("oom_reaper: close race with exiting task")
: reduced frequency of needlessly selecting next OOM victim, but was
: calling mmput_async() when atomic_inc_not_zero() failed.
because it doesn't explain that the patch potentially fixes a kernel
crash.
And the changelog for this above patch is similarly crappy - it fails
to described the end-user visible effects of the bug which is being
fixed. Please *always* do this. Always always always.
Please send me a complete changelog for this patch, thanks.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>