Re: [PATCH] mm, memory_failure: only send BUS_MCEERR_AO to early-kill process

wetp
2020-05-29T05:56:33Z

On 2020/5/29 上午10:12, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Thu, May 28, 2020 at 02:50:09PM +0800, wetp wrote:
>> On 2020/5/28 上午10:22, HORIGUCHI NAOYA(堀口 直也) wrote:
>>> Hi Zhang,
>>>
>>> Sorry for my late response.
>>>
>>> On Tue, May 26, 2020 at 03:06:41PM +0800, Wetp Zhang wrote:
>>>> From: Zhang Yi <wetpzy@gmail.com>
>>>>
>>>> If a process don't need early-kill, it may not care the BUS_MCEERR_AO.
>>>> Let the process to be killed when it really access the corrupted memory.
>>>>
>>>> Signed-off-by: Zhang Yi <wetpzy@gmail.com>
>>> Thank you for pointing this. This looks to me a bug (per-process flag
>>> is ignored when system-wide flag is set).
>> The flag is not problem for me.
>>
>> In my case, two processes share memory with no any flag setting, both will
>> be killed when only one
>>
>> access the fail memory.
> Thanks, now your problem seems clearer.
>
> It seems that this happens because in "Action Required" case kill_proc()
> takes the first branch for current process, while it takes the else branch
> for other affected processes:
>
> static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
> {
> ...
>
> if ((flags & MF_ACTION_REQUIRED) && t->mm == current->mm) {
> ret = force_sig_mceerr(BUS_MCEERR_AR, (void __user *)tk->addr,
> addr_lsb);
> } else {
> /*
> * Don't use force here, it's convenient if the signal
> * can be temporarily blocked.
> * This could cause a loop when the user sets SIGBUS
> * to SIG_IGN, but hopefully no one will do that?
> */
> ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
> addr_lsb, t); /* synchronous? */
> }
>
> Sending SIGBUS with BUS_MCEERR_AO for action optional error is strange, so
> maybe this logic should be like this:
>
>
> if (flags & MF_ACTION_REQUIRED) {
> if (t->mm == current->mm)
> ret = force_sig_mceerr(BUS_MCEERR_AR, (void __user *)tk->addr,
> addr_lsb);
> /* send no signal to non-current processes */
Ok, this can solve my problem.

> } else {
> /*
> * Don't use force here, it's convenient if the signal
> * can be temporarily blocked.
> * This could cause a loop when the user sets SIGBUS
> * to SIG_IGN, but hopefully no one will do that?
> */
> ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
> addr_lsb, t); /* synchronous? */
> }
>
>>>> ---
>>>> mm/memory-failure.c | 7 ++++---
>>>> 1 file changed, 4 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>>> index a96364be8ab4..2db13d48865c 100644
>>>> --- a/mm/memory-failure.c
>>>> +++ b/mm/memory-failure.c
>>>> @@ -210,7 +210,7 @@ static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
>>>> {
>>>> struct task_struct *t = tk->tsk;
>>>> short addr_lsb = tk->size_shift;
>>>> - int ret;
>>>> + int ret = 0;
>>>>
>>>> pr_err("Memory failure: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
>>>> pfn, t->comm, t->pid);
>>>> @@ -225,8 +225,9 @@ static int kill_proc(struct to_kill *tk, unsigned long pfn, int flags)
>>>> * This could cause a loop when the user sets SIGBUS
>>>> * to SIG_IGN, but hopefully no one will do that?
>>>> */
>>>> - ret = send_sig_mceerr(BUS_MCEERR_AO, (void __user *)tk->addr,
>>>> - addr_lsb, t); /* synchronous? */
>>>> + if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
>>>> + ret = send_sig_mceerr(BUS_MCEERR_AO,
>>>> + (void __user *)tk->addr, addr_lsb, t);
>>> kill_proc() could be called only for processes that are selected by
>>> collect_procs() with task_early_kill(). So I think that we should fix
>>> task_early_kill(), maybe by reordering sysctl_memory_failure_early_kill
>>> check and find_early_kill_thread() check.
>>>
>>> static struct task_struct *task_early_kill(struct task_struct *tsk,
>>> int force_early)
>>> {
>>> struct task_struct *t;
>>> if (!tsk->mm)
>>> return NULL;
>>> if (force_early)
>>> return tsk;
>> The force_early is rely the flag MF_ACTION_REQUIRED, so it is always true
>> when MCE occurs.
>>
>> This leads always sending SIGBUS to processes even if those are not current
>> or no flag setting.
>>
>>  I think it could keep the non-current processes which has no flag setting
>> running.
>>
>>
>> Besides, base on your recommendation I reorder the force_early check and
>> find_early_kill_thread()
>>
>> check, to send the signal to the right thread.
> Sorry, my previous comment around task_early_kill() is for a separate problem,
> so I'll try some fix on this later.
Thanks.

Should me send the patch V2 for my problem alone?  Or you will fix it
with task_early_kill() together ？

> Thanks,
> Naoya Horiguchi