Messages in this thread | | | Date | Wed, 01 Sep 2010 15:11:23 -0600 | From | Tim Gardner <> | Subject | Re: nfsd deadlock, 2.6.36-rc3 |
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On 09/01/2010 02:55 PM, Neil Brown wrote: > On Wed, 1 Sep 2010 12:54:01 -0400 > "J. Bruce Fields"<bfields@fieldses.org> wrote: > >> On Wed, Sep 01, 2010 at 09:39:55AM -0600, Tim Gardner wrote: >>> I've been pursuing a simple reproducer for an NFS lockup that shows >>> up under stress. There is a bunch of info (some of it extraneous) in >>> http://bugs.launchpad.net/bugs/561210. I can reproduce it by writing >>> loop mounted NFS exports: >>> >>> /etc/fstab: 127.0.0.1:/srv /mnt/srv nfs rw 0 2 >>> /etc/exports: /srv 127.0.0.1(rw,insecure,no_subtree_check) >>> >>> See the attached scripts test_master.sh and test_client.sh. I simply >>> repeat './test_master.sh wait' until nfsd locks up, typically within >>> 1-3 cycles, e.g., >> >> Without looking at the dmesg and scripts carefully to confirm, one >> possible explanation is a deadlock when the server can't allocate memory >> required to service client requests, memory which the client itself >> needs to free by writing back dirty pages, but can't because the server >> isn't processing its writes. > > Having looked closely I'd say it is almost certainly this issue. > nfsd thread 1266 is in zone_reclaim waiting on a page to be written out so > the memory can be reused. > The other nfsd threads are blocking on a mutex held by 1266. > The dd processes are waiting for pages to be written to the server > > The particular page that 1266 is waiting on is almost certainly a page on an > NFS file, so you have a cyclic deadlock. > >> >> For that reason we just don't support loopback mounts--they're OK for >> light testing, but it would be difficult to make them completely robust >> under load. > > I wonder if we could use 'containers' to partition available memory between > 'nfsd threads' and 'everything else'?? Probably not worth the effort. > > NeilBrown >
I'm currently working with my support folks to reproduce this using the exact same configuration as the customer, e.g., an NFS server (running as a guest on a VMWare ESX host) serving multiple gigabit clients.
I assume that is a reasonable scenario?
rtg -- Tim Gardner tim.gardner@canonical.com
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