Messages in this thread | | | Date | Thu, 7 Jul 2016 15:34:34 +0200 | From | Greg Kurz <> | Subject | Re: [PATCH 0/3] fs/9p: fix setattr/getattr issues with open files |
| |
On Thu, 7 Jul 2016 14:35:40 +0200 Dominique Martinet <dominique.martinet@cea.fr> wrote:
> Hi Greg, >
Hi Dominique,
> Greg Kurz wrote on Mon, Jul 04, 2016 at 05:08:49PM +0200: > > On Mon, 4 Jul 2016 16:16:55 +0200 > > Dominique Martinet <dominique.martinet@cea.fr> wrote: > > > > > I *think* this introduces a race somewhere, I'm getting errors like: > > > cat: f.05: No such file or directory > > > cat: f.14: No such file or directory > > > cat: f.13: No such file or directory > > > cat: f.39: No such file or directory > > > cat: f.05: No such file or directory > > > > > > > > > when doing: > > > for file in {01..50}; do touch f.${file}; done > > > seq 1 1000 | xargs -n 1 -P 25 -I{} cat f.* > /dev/null > > Ok so, tested with the first two patches and I can't seem to hit any > problem with the qemu server at least (I'd need more time to fix > ganesha's 9p tcp/rdma server before I could blame the client in any way) >
I'm not surprised: patch 1 simply adds a "fallback" lookup to the existing code, and patch 2 changes this "fallback" lookup only.
Bad things can come with patch 3 because it really changes the lookup logic.
> > The last patch looks good to me, I think it only makes an existing race > more visible... What I think could happen is: > process 1 has file open > process 2 tries to open file, sees fid open > process 1 closes file/clunk fids > process 2 tries to clone now-clunked fid and gets ENOENT >
I'll try to have a look with this scenario in mind.
> > I'm afraid I just found out my hypervisor is no longer recent enough for > gdb kernel scripts (gdb 7.6 and python 2.7.5 in el7 compared to the > apparently required 7.7 and 2.7.6 respectively...), and I don't see > anything obvious with just debug messages/adding a few printks (wasn't > able to confirm where exactly that ENOENT comes from or if my theory is > even close to the truth) > > I'd like to spend more time on it but don't think I'll be able to for a > couple of weeks ; sorry about that. >
No problem. My plate is full anyway until I go into a 1-month vacation, starting end of July. And I'm currently targeting QEMU 2.8 for the server side fixes: we have plenty of time to fix this.
> > Were you able to reproduce the problem? >
Yes ! I get it every time :)
> Thanks,
I really appreciate your assistance since v9fs-devel is really quiet these days.
Cheers.
-- Greg
| |