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

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Date: Thu, 9 May 2024 09:40:31 -0700
From: Jane Chu <jane.chu@...cle.com>
To: Miaohe Lin <linmiaohe@...wei.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 5/8/2024 7:54 PM, Miaohe Lin wrote:

> 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.

Yes, will do.

thanks!

-jane

> 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);
>>   }
>>   
>>   /*
>>
>