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From: Miklos Szeredi <miklos@szeredi.hu>
To: Kirill Smelkov <kirr@nexedi.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>,
	linux-fsdevel@vger.kernel.org,
	fuse-devel <fuse-devel@lists.sourceforge.net>,
	Han-Wen Nienhuys <hanwen@google.com>,
	Jakob Unterwurzacher <jakobunt@gmail.com>,
	stable <stable@vger.kernel.org>
Subject: Re: [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it
Date: Tue, 26 Feb 2019 16:14:22 +0100	[thread overview]
Message-ID: <CAJfpegtgNb2FpE=gHSVTmX5EWRJtDp-a5HZO2VS2_eHjPpp=fw@mail.gmail.com> (raw)
In-Reply-To: <20190219094147.32734-1-kirr@nexedi.com>

On Tue, Feb 19, 2019 at 10:42 AM Kirill Smelkov <kirr@nexedi.com> wrote:
>
> A successful call to NOTIFY_RETRIEVE by filesystem carries promise from
> the kernel to send back NOTIFY_REPLY message. However if the filesystem
> is not reading requests with fuse_conn->max_pages capacity,

That's a violation of the contract by the fuse server, not the kernel.

> fuse_dev_do_read might see that the "request is too large" and decide to
> "reply with an error and restart the read". "Reply with an error" has
> underlying assumption that there is a "requester thread" that is waiting
> for request completion, which is true for most requests, but is not true
> for NOTIFY_REPLY: NOTIFY_RETRIEVE handler completes with OK status right
> after it could successfully queue NOTIFY_REPLY message without waiting
> for NOTIFY_REPLY completion. This leads to situation when filesystem
> requested to retrieve inode data with NOTIFY_RETRIEVE, got err=OK for
> that notification request, but NOTIFY_REPLY is not coming back.
>
> More, since there is no "requester thread" to handle the error, the
> situation shows itself as /sys/fs/fuse/connections/X/waiting=1 _and_
> /dev/fuse read(s) queued. Which is misleading since NOTIFY_REPLY request
> was removed from pending queue and abandoned.

Now I don't understand how that would happen.   If the request is
abandoned, its refcount should go down to zero and the num_waiting
count decremented accordingly.

Thanks,
Miklos

  reply	other threads:[~2019-02-26 15:14 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-19  9:42 [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it Kirill Smelkov
2019-02-26 15:14 ` Miklos Szeredi [this message]
2019-02-27 20:02   ` Kirill Smelkov
2019-02-27 20:26     ` Miklos Szeredi
2019-02-27 20:39       ` Kirill Smelkov
2019-02-28  8:10         ` Miklos Szeredi
2019-02-28 11:48           ` Kirill Smelkov
2019-02-28 11:50             ` [PATCH 2/2] fuse: require /dev/fuse reads to have enough buffer capacity as negotiated Kirill Smelkov
2019-03-07  9:34             ` [RESEND, PATCH v2] fuse: Don't drop NOTIFY_REPLY if we promised it Kirill Smelkov
2019-03-14 10:45               ` [RESEND3, PATCH 0/2] fuse: don't stuck clients on retrieve_notify with size > max_write Kirill Smelkov
2019-03-14 10:46                 ` [PATCH 1/2] fuse: retrieve: cap requested size to negotiated max_write Kirill Smelkov
2019-03-14 10:46                 ` [PATCH 2/2] fuse: require /dev/fuse reads to have enough buffer capacity as negotiated Kirill Smelkov

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