linux-kernel - Re: [PATCH] uprobes: wait for mmap

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Message-ID: <56E2DD23.5070703@suse.cz>
Date:	Fri, 11 Mar 2016 15:58:43 +0100
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] uprobes: wait for mmap_sem for write killable

On 02/29/2016 06:42 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
>
> xol_add_vma needs mmap_sem for write. If the waiting task gets killed by
> the oom killer it would block oom_reaper from asynchronous address space
> reclaim and reduce the chances of timely OOM resolving. Wait for the
> lock in the killable mode and return with EINTR if the task got killed
> while waiting.
>
> Do not warn in dup_xol_work if __create_xol_area failed due to fatal
> signal pending because this is usually considered a kernel issue.
>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>   kernel/events/uprobes.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 8eef5f55d3f0..fb4a6bcc88ce 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1130,7 +1130,9 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
>   	struct vm_area_struct *vma;
>   	int ret;
>
> -	down_write(&mm->mmap_sem);
> +	if (down_write_killable(&mm->mmap_sem))
> +		return -EINTR;
> +
>   	if (mm->uprobes_state.xol_area) {
>   		ret = -EALREADY;
>   		goto fail;
> @@ -1468,7 +1470,8 @@ static void dup_xol_work(struct callback_head *work)
>   	if (current->flags & PF_EXITING)
>   		return;
>
> -	if (!__create_xol_area(current->utask->dup_xol_addr))
> +	if (!__create_xol_area(current->utask->dup_xol_addr) &&
> +			!fatal_signal_pending(current)
                                                       ^ missing ")"

Other than that,
Acked-by: Vlastimil Babka <vbabka@...e.cz>

>   		uprobe_warn(current, "dup xol area");
>   }
>
>