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SubjectRe: Make the get_user_pages interruptible
On Thu, 20 Nov 2008 14:03:36 -0800
Ying Han <yinghan@google.com> wrote:

> make get_user_pages interruptible
> The initial implementation of checking TIF_MEMDIE covers the cases of OOM
> killing. If the process has been OOM killed, the TIF_MEMDIE is set and it
> return immediately. This patch includes:
>
> 1. add the case that the SIGKILL is sent by user processes. The process can
> try to get_user_pages() unlimited memory even if a user process has sent a
> SIGKILL to it(maybe a monitor find the process exceed its memory limit and
> try to kill it). In the old implementation, the SIGKILL won't be handled
> until the get_user_pages() returns.
>
> 2. change the return value to be ERESTARTSYS. It makes no sense to return
> ENOMEM if the get_user_pages returned by getting a SIGKILL signal.
> Considering the general convention for a system call interrupted by a
> signal is ERESTARTNOSYS, so the current return value is consistant to that.
>
> Signed-off-by: Paul Menage <menage@google.com>
> Ying Han <yinghan@google.com>
>
>

This isn't right?

> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1218,12 +1218,11 @@ int __get_user_pages(struct task_struct *tsk, struct m
> struct page *page;
>
> /*
> - * If tsk is ooming, cut off its access to large memory
> - * allocations. It has a pending SIGKILL, but it can't
> - * be processed until returning to user space.
> + * If we have a pending SIGKILL, don't keep
> + * allocating memory.
> */
> - if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
> - return i ? i : -ENOMEM;
> + if (sigkill_pending(current))
> + return -ERESTARTSYS;
>
> if (write)
> foll_flags |= FOLL_WRITE;

If this function has already put some page*'s into *pages, they will be
leaked. The function fails to release those pages and it does not
provide sufficient information to callers to allow them to release the
pages.

I thought I already mentioned that last time I saw this patch?


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