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Subject: Re: [PATCH v2] mm/vmscan: fix infinite loop in drop_slab_node
To:     Matthew Wilcox <willy@infradead.org>,
        Chris Down <chris@chrisdown.name>
Cc:     zangchunxin@bytedance.com, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Muchun Song <songmuchun@bytedance.com>
References: <20200909152047.27905-1-zangchunxin@bytedance.com>
 <16906d44-9e3c-76a1-f1a9-ced61e865467@suse.cz>
 <20200909214724.GA1577471@chrisdown.name>
 <20200909215209.GP6583@casper.infradead.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <4e022a8c-68da-a322-4101-926a0bb9d44b@suse.cz>
Date:   Thu, 10 Sep 2020 00:13:48 +0200
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On 9/9/20 11:52 PM, Matthew Wilcox wrote:
> 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.

Ah actually it was me who thought fatal_signal_pending() was only for SIGKILL,
OOM and whatnot. Sorry for the noise.

>         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));
> }
>