Messages in this thread | | | Date | Mon, 1 Mar 2021 11:01:57 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH] net: 9p: free what was emitted when read count is 0 |
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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
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