linux-kernel - Re: [PATCH v2] mm/vmscan: fix infinite loop in drop_slab

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Date:   Wed, 9 Sep 2020 22:56:16 +0100
From:   Chris Down <chris@...isdown.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, zangchunxin@...edance.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v2] mm/vmscan: fix infinite loop in drop_slab_node

Matthew Wilcox writes:
>On Wed, Sep 09, 2020 at 10:47:24PM +0100, Chris Down wrote:
>> Vlastimil Babka writes:
>> > - Exit also on other signals such as SIGABRT, SIGTERM? If I write to drop_caches
>> > and think it's too long, I would prefer to kill it by ctrl-c and not just kill
>>
>> Oh dear, fatal_signal_pending() doesn't consider cases with no more
>> userspace instructions due to SIG_DFL on TERM/INT etc, that seems misleading
>> :-( I had (naively) believed it internally checks the same set as
>> TASK_KILLABLE.
>>
>> Chuxin, Muchun, can you please make it work using TASK_KILLABLE in a similar
>> way to how schedule_timeout_killable and friends do it instead, so that
>> other signals will be caught?
>
>You're mistaken.
>
>        if (sig_fatal(p, sig) &&
>            !(signal->flags & SIGNAL_GROUP_EXIT) &&
>            !sigismember(&t->real_blocked, sig) &&
>            (sig == SIGKILL || !p->ptrace)) {
>...
>                                sigaddset(&t->pending.signal, SIGKILL);
>
>static inline int __fatal_signal_pending(struct task_struct *p)
>{
>        return unlikely(sigismember(&p->pending.signal, SIGKILL));
>}

Oh great, that makes things way easier. Thanks!