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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [mm 4.15-rc8] Random oopses under memory pressure.
Date: Tue, 16 Jan 2018 11:30:54 -0800	[thread overview]
Message-ID: <CA+55aFyThu2FrxUh-4WrGHAd_QX=v1H2L+UNnUkks7n+dSvcfA@mail.gmail.com> (raw)
In-Reply-To: <7f100b0f-3588-be25-41f6-a0e4dde27916@linux.intel.com>

On Tue, Jan 16, 2018 at 12:06 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
> On 01/15/2018 06:14 PM, Linus Torvalds wrote:
>> But I'm adding Dave Hansen explicitly to the cc, in case he has any
>> ideas. Not because I blame him, but he's touched the sparsemem code
>> fairly recently, so maybe he'd have some idea on adding sanity
>> checking to the sparsemem version of pfn_to_page().
>
> I swear I haven't touched it lately!

Heh. I did

    git blame -C mm/sparse.c | grep 2017

and your name shows up at the beginning a lot because of commit
c4e1be9ec113 ("mm, sparsemem: break out of loops early").

And Michal Hocko (who shows up even more) was already on the cc.

> I'm not sure I'd go after pfn_to_page().  *Maybe* if we were close to
> the places where we've done a pfn_to_page(), but I'm not seeing those.

Fair enough. I just wanted to add debugging, looked at Tetsuo's
config, and went "no way am I adding debugging to the sparsemem case
because it's so confusing".

That said, I also started looking at "kmap_to_page()". That's
something that is *really* different with HIGHMEM, and while most of
the users are in random drivers that do crazy things, I do note that
one of the users is in mm/swap.c.

That thing goes back to commit 5a178119b0fb ("mm: add support for
direct_IO to highmem pages") and was only used for swap_writepage(),
if I read this right.

That swap_writepage() use of kmap()'ed patches was removed some time
later in commit 62a8067a7f35 ("bio_vec-backed iov_iter"), but the
crazy kmap_to_page() thing remained.

I see nothing actively wrong in there, but it really feels like a
"that is all bogus" thing to me.

> Did anyone else notice the
>
>         [   31.068198]  ? vmalloc_sync_all+0x150/0x150
>
> present in a bunch of the stack traces?  That should be pretty uncommon.

No, didn't notice that. And yes, vmalloc_sync_all() might be interesting.

>  Is it just part of the normal do_page_fault() stack and the stack
> dumper picks up on it?

I don't think so. It should *not* happen normally. The fact that it
shows up in the trace means it happened that time.

It doesn't seem HIGHMEM-related, though. Or maybe the highmem signal
is bogus too, and it's just that Tetsuo's reproducer needs magical
timing.

             Linus

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  parent reply	other threads:[~2018-01-16 19:30 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <201801091939.JDJ64598.HOMFQtOFSOVLFJ@I-love.SAKURA.ne.jp>
     [not found] ` <201801102049.BGJ13564.OOOMtJLSFQFVHF@I-love.SAKURA.ne.jp>
     [not found]   ` <20180110124519.GU1732@dhcp22.suse.cz>
     [not found]     ` <201801102237.BED34322.QOOJMFFFHVLSOt@I-love.SAKURA.ne.jp>
     [not found]       ` <20180111135721.GC1732@dhcp22.suse.cz>
2018-01-11 14:11         ` [mm? 4.15-rc7] " Tetsuo Handa
2018-01-11 14:21           ` Michal Hocko
2018-01-11 14:37             ` Tetsuo Handa
2018-01-12  1:31             ` [mm " Tetsuo Handa
2018-01-12  1:42               ` Linus Torvalds
2018-01-12 11:22                 ` Tetsuo Handa
2018-01-14 11:54                   ` Tetsuo Handa
2018-01-15 23:05                     ` Linus Torvalds
2018-01-16  1:15                       ` [mm 4.15-rc8] " Tetsuo Handa
2018-01-16  2:14                         ` Linus Torvalds
2018-01-16  8:06                           ` Dave Hansen
2018-01-16  8:37                             ` Ingo Molnar
2018-01-16 19:30                             ` Linus Torvalds [this message]
2018-01-16 17:33                           ` Tetsuo Handa
2018-01-16 19:34                             ` Linus Torvalds
2018-01-17 11:08                               ` Tetsuo Handa
2018-01-11 18:11           ` [mm? 4.15-rc7] " Linus Torvalds
2018-01-11 20:59             ` Tetsuo Handa

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