linux-kernel - Re: [PATCH 1/3] mm/memory-failure: try to send SIGBUS even if unmap failed

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Message-ID: <d5dc761e-3f66-99a3-5325-dd2f161235cf@huawei.com>
Date: Thu, 9 May 2024 10:54:58 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Jane Chu <jane.chu@...cle.com>, <nao.horiguchi@...il.com>,
	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mm/memory-failure: try to send SIGBUS even if unmap
 failed

On 2024/5/2 7:24, Jane Chu wrote:
> For years when it comes down to kill a process due to hwpoison,
> a SIGBUS is delivered only if unmap has been successful.
> Otherwise, a SIGKILL is delivered. And the reason for that is
> to prevent the involved process from accessing the hwpoisoned
> page again.
> 
> Since then a lot has changed, a hwpoisoned page is marked and
> upon being re-accessed, the process will be killed immediately.
> So let's take out the '!unmap_success' factor and try to deliver
> SIGBUS if possible.
> 
> Signed-off-by: Jane Chu <jane.chu@...cle.com>
> ---
>  mm/memory-failure.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 9e62a00b46dd..7fcf182abb96 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -519,19 +519,14 @@ void add_to_kill_ksm(struct task_struct *tsk, struct page *p,
>   * Also when FAIL is set do a force kill because something went
>   * wrong earlier.
>   */
> -static void kill_procs(struct list_head *to_kill, int forcekill, bool fail,
> +static void kill_procs(struct list_head *to_kill, int forcekill,
>  		unsigned long pfn, int flags)
>  {
>  	struct to_kill *tk, *next;
>  
>  	list_for_each_entry_safe(tk, next, to_kill, nd) {
>  		if (forcekill) {
> -			/*
> -			 * In case something went wrong with munmapping
> -			 * make sure the process doesn't catch the
> -			 * signal and then access the memory. Just kill it.
> -			 */
> -			if (fail || tk->addr == -EFAULT) {
> +			if (tk->addr == -EFAULT) {
>  				pr_err("%#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
>  				       pfn, tk->tsk->comm, tk->tsk->pid);
>  				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
> @@ -1666,7 +1661,7 @@ static bool hwpoison_user_mappings(struct page *p, unsigned long pfn,
>  	 */

There is comment above the forcekill saying:

    When there was a problem unmapping earlier use a more force-full
uncatchable kill to prevent any accesses to the poisoned memory.

This might need to be changed too.
Thanks.
.

>  	forcekill = PageDirty(hpage) || (flags & MF_MUST_KILL) ||
>  		    !unmap_success;
> -	kill_procs(&tokill, forcekill, !unmap_success, pfn, flags);
> +	kill_procs(&tokill, forcekill, pfn, flags);
>  
>  	return unmap_success;
>  }
> @@ -1730,7 +1725,7 @@ static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
>  		unmap_mapping_range(mapping, start, size, 0);
>  	}
>  
> -	kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
> +	kill_procs(to_kill, flags & MF_MUST_KILL, pfn, flags);
>  }
>  
>  /*
>