From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To: Dominique Martinet <asmadeus@codewreck.org>
Cc: Eric Van Hensbergen <ericvh@gmail.com>,
Latchesar Ionkov <lucho@ionkov.net>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
v9fs-developer@lists.sourceforge.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: 9p: free what was emitted when read count is 0
Date: Mon, 1 Mar 2021 11:01:57 +0800 [thread overview]
Message-ID: <20210301110157.19d9ad4e@xhacker.debian> (raw)
In-Reply-To: <YDxWrB8AoxJOmScE@odin>
On Mon, 1 Mar 2021 11:51:24 +0900 Dominique Martinet wrote:
>
>
> Jisheng Zhang wrote on Mon, Mar 01, 2021 at 10:33:36AM +0800:
> > I met below warning when cating a small size(about 80bytes) txt file
> > on 9pfs(msize=2097152 is passed to 9p mount option), the reason is we
> > miss iov_iter_advance() if the read count is 0, so we didn't truncate
> > the pipe, then iov_iter_pipe() thinks the pipe is full. Fix it by
> > calling iov_iter_advance() on the iov_iter "to" even if read count is 0
>
> Hm, there are plenty of other error cases that don't call
> iov_iter_advance() and shouldn't trigger this warning ; I'm not sure
> just adding one particular call to this is a good solution.
Per my understanding of iov_iter, we need to call iov_iter_advance()
even when the read out count is 0. I believe we can see this common style
in other fs.
>
>
> How reproducible is this? From the description it should happen
100%
> everytime you cat a small file? (I'm surprised cat uses sendfile, what
it happened every time when catting a small file.
> cat version? coreutils' doesn't seem to do that on their git)
busybox cat
>
> What kernel version do you get this on? Bonus points if you can confirm
5.11 and the latest linus tree
> this didn't use to happen, and full points for a bisect.
>
>
> (cat on a small file is something I do all the time in my tests, I'd
> like to be able to reproduce to understand the issue better as I'm not
> familiar with that part of the code)
Per my check, it can be 100% reproduced with busybox cat + "msize=2097152"
mount option. NOTE: msize=2097152 isn't a magic number it can be other
numbers which can ensure zerocopy code path is executed: p9_client_read_once
->p9_client_zc_rpc()
Thanks
next prev parent reply other threads:[~2021-03-01 3:03 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-01 2:33 [PATCH] net: 9p: free what was emitted when read count is 0 Jisheng Zhang
2021-03-01 2:51 ` Dominique Martinet
2021-03-01 3:01 ` Jisheng Zhang [this message]
2021-03-02 4:38 ` Dominique Martinet
2021-03-02 7:39 ` Jisheng Zhang
2021-03-02 8:08 ` Dominique Martinet
2021-03-02 9:22 ` Jisheng Zhang
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