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From: Nikolaus Rath <Nikolaus@rath.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
        fuse-devel <fuse-devel@lists.sourceforge.net>,
        linux-fsdevel@vger.kernel.org,
        Sahitya Tummala <stummala@codeaurora.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [fuse-devel] Reading from fuse pipe fails with EBADFD
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Date: Mon, 31 Dec 2018 10:56:30 +0000
In-Reply-To: <87lg4bncnz.fsf@vostro.rath.org> (Nikolaus Rath's message of
        "Wed, 26 Dec 2018 22:30:56 +0000")
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On Dec 26 2018, Nikolaus Rath <Nikolaus@rath.org> wrote:
>>> >> > When testing FUSE under heavy load, I am occasionally getting EBAD=
FD
>>> >> > errors when reading from the fuse pipe.
>>> >
>>> > EBADFD or EBADF?
>>>
>>> EBADF ("Bad file descriptor"), sorry.
>>
>> Can you run the thing with "strace -f  ..."?
>
> Apologies for the delayed response. I have been trying to reproduce this
> but have instead run into another problem: the *client* getting spurious
> EBADF warnings. I am not sure if this is related or unrelated, and it
> has been hard to debug because it does not happen under strace:
[..]

I believe I have figured it out. I was mistakenly assuming that the bad
file descriptor was the fuse pipe - but it was actually the target file
descriptor (I managed to completely forget that splice works on two file
descriptors).

The root cause was mistakenly closing a file descriptor twice and not
checking the return value. Because of the missing return value check,
the error went unnoticed almost all the time - except when a different
thread managed to re-use the fd for different purposes between the first
and second close.

Apologies for taking everyone's time for what was actually a filesystem
bug.


Best,
-Nikolaus

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