From: Nikolaus Rath <Nikolaus@rath.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: fuse-devel <fuse-devel@lists.sourceforge.net>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Miklos Szeredi <mszeredi@redhat.com>
Subject: Re: [fuse-devel] fuse: trying to steal weird page
Date: Tue, 08 Jan 2019 10:35:40 +0000 [thread overview]
Message-ID: <87ef9nighv.fsf@thinkpad.rath.org> (raw)
In-Reply-To: <CAJfpegu_qxcaQToDpSmcW_ncLb_mBX6f75RTEn6zbsihqcg=Rw@mail.gmail.com> (Miklos Szeredi's message of "Tue, 8 Jan 2019 09:27:35 +0100")
On Jan 08 2019, Miklos Szeredi <miklos@szeredi.hu> wrote:
> On Mon, Jan 7, 2019 at 10:05 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
>>
>> On Jan 07 2019, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> > On Wed, Dec 26, 2018 at 10:44 PM Nikolaus Rath <Nikolaus@rath.org> wrote:
>> >>
>> >> Hi,
>> >>
>> >> I am seeing relatively regular occurences of
>> >>
>> >> $ sudo dmesg | tail
>> >> [21929.138815] fuse: trying to steal weird page
>> >> [21929.138821] page=00000000a7dd2617 index=64 flags=17fffc0000000ad,
>> >> count=1, mapcount=0, mapping= (null)
>> >> [21930.647338] fuse: trying to steal weird page
>> >> [21930.647345] page=00000000a07f32af index=2848
>> >> flags=17fffc0000000ad, count=1, mapcount=0, mapping= (null)
>> >> [21932.338873] fuse: trying to steal weird page
>> >> [21932.338879] page=0000000067e3a012 index=64 flags=17fffc0000000ad,
>> >> count=1, mapcount=0, mapping= (null)
>> >> [21933.930703] fuse: trying to steal weird page
>> >> [21933.930710] page=00000000046feb25 index=845
>> >> flags=17fffc0000000ad, count=1, mapcount=0, mapping= (null)
>> >> [21936.163174] fuse: trying to steal weird page
>> >> [21936.163180] page=00000000fb80fe27 index=0 flags=17fffc0000000ad,
>> >> count=1, mapcount=0, mapping= (null)
>> >
>> > The page has the PG_dity and PG_waiters flags set which are
>> > incompatible with stealing. page_cache_pipe_buf_steal() does
>> > apparently filter out dirty ones, so it's not a regular file that we
>> > are trying to streal the page from. So the question is: what is the
>> > source of the splice()?
>>
>> Hmm. I think it has to be a regular file. But as I mentioned in my other
>> email, I did have a race condition where fd's were closed
>> incorrectly. Is it possible that this also triggered the above,
>> i.e. that the fd was closed sometime during splice?
>
> Close during a syscall that uses the fd is not an issue, because a ref
> to the file is acquired. So the race is between the close() and the
> internal fget(); if the close() wins then fget() will fail and the
> syscall will return EBADF. If the fget() wins, then the syscall can
> run normally despite the fact that the fd was closed.
>
> Can you tell me what filesystem is the regular file (the one being
> spliced into fuse) is on?
It's ext4.
> It actually has to be a regular file, since AFAIK nothing else has
> dirty pages. It could be using something other than
> page_cache_pipe_buf_steal(), or there's some other mechanism that lets
> the page be dirtied after being unmapped, though that looks
> impossible...
I can't meaningfully comment on that, sorry...
Best,
-Nikolaus
--
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»Time flies like an arrow, fruit flies like a Banana.«
next prev parent reply other threads:[~2019-01-08 10:35 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-26 21:43 fuse: trying to steal weird page Nikolaus Rath
2019-01-07 8:28 ` [fuse-devel] " Miklos Szeredi
2019-01-07 21:05 ` Nikolaus Rath
2019-01-08 8:27 ` Miklos Szeredi
2019-01-08 10:35 ` Nikolaus Rath [this message]
2019-01-09 8:07 ` Miklos Szeredi
[not found] ` <CAJfpegtiXDgSBWN8MRubpAdJFxy95X21nO_yycCZhpvKLVePRA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-01-11 15:39 ` Nikolaus Rath
2019-01-11 15:39 ` [fuse-devel] " Nikolaus Rath
2019-02-10 22:05 ` Nikolaus Rath
2019-02-12 14:57 ` Miklos Szeredi
2019-02-12 21:28 ` Nikolaus Rath
2019-02-25 21:41 ` Nikolaus Rath
2019-02-26 12:57 ` Miklos Szeredi
2019-02-26 13:30 ` Miklos Szeredi
2020-05-02 19:09 Nikolaus Rath
2020-05-02 19:52 ` Nikolaus Rath
2020-05-03 3:26 ` Matthew Wilcox
2020-05-03 8:43 ` [fuse-devel] " Nikolaus Rath
2020-05-03 10:27 ` Matthew Wilcox
2020-05-03 18:28 ` Gabriel Krisman Bertazi
2020-05-03 20:06 ` Matthew Wilcox
2020-05-03 20:25 ` Nikolaus Rath
2020-05-06 13:57 ` Vlastimil Babka
2020-05-03 21:34 ` Hugh Dickins
2020-05-18 12:45 ` Miklos Szeredi
2020-05-18 14:48 ` Matthew Wilcox
2020-05-18 14:58 ` Miklos Szeredi
2020-05-18 15:26 ` Matthew Wilcox
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