On Tue, 2016-06-07 at 13:30 -0400, Oleg Drokin wrote: > On Jun 7, 2016, at 1:10 PM, Jeff Layton wrote: > > > > > On Tue, 2016-06-07 at 11:37 -0400, Oleg Drokin wrote: > > > > > > Hello! > > > > > > I've been trying to better understand this problem I was having where sometimes > > > a formerly NFS-exported mountpoint becomes unmountable (after nfsd stop). > > > > > > I finally traced it to a leaked filedescriptor that was allocated from > > > nfsd4_open()->nfsd4_process_open2()->nfs4_get_vfs_file()->nfsd_open(). > > > > > > Also together with it we see leaked credentials allocated along the same path from > > > fh_verify() and groups allocated from svcauth_unix_accept()->groups_alloc() that > > > are presumably used by the credentials. > > > > > > Unfortunately I was not able to make total sense out of the state handling in nfsd, > > > but it's clear that one of the file descriptors inside struct nfs4_file is > > > lost. I added a patch like this (always a good idea, so surprised it was not > > > there already): > > > @@ -271,6 +274,9 @@ static void nfsd4_free_file_rcu(struct rcu_head *rcu) > > > { > > > struct nfs4_file *fp = container_of(rcu, struct nfs4_file, fi_rcu); > > > > > > + WARN_ON(fp->fi_fds[0]); > > > + WARN_ON(fp->fi_fds[1]); > > > + WARN_ON(fp->fi_fds[2]); > > > kmem_cache_free(file_slab, fp); > > > } > > > > > > And when the problem is hit, I am also triggering (Always this one which is fd[1]) > > > [ 3588.143002] ------------[ cut here ]------------ > > > [ 3588.143662] WARNING: CPU: 5 PID: 9 at /home/green/bk/linux/fs/nfsd/nfs4state.c:278 nfsd4_free_file_rcu+0x65/0x80 [nfsd] > > > [ 3588.144947] Modules linked in: loop rpcsec_gss_krb5 joydev acpi_cpufreq tpm_tis i2c_piix4 tpm virtio_console pcspkr nfsd ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm floppy serio_raw virtio_blk > > > [ 3588.147135] CPU: 5 PID: 9 Comm: rcuos/0 Not tainted 4.7.0-rc1-vm-nfs+ #120 > > > [ 3588.153826] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > > > [ 3588.153830] 0000000000000286 00000000e2d5ccdf ffff88011965bd50 ffffffff814a11a5 > > > [ 3588.153832] 0000000000000000 0000000000000000 ffff88011965bd90 ffffffff8108806b > > > [ 3588.153834] 0000011600000000 ffff8800c476a0b8 ffff8800c476a048 ffffffffc0110fc0 > > > [ 3588.153834] Call Trace: > > > [ 3588.153839] [] dump_stack+0x86/0xc1 > > > [ 3588.153841] [] __warn+0xcb/0xf0 > > > [ 3588.153852] [] ? trace_raw_output_fh_want_write+0x60/0x60 [nfsd] > > > [ 3588.153853] [] warn_slowpath_null+0x1d/0x20 > > > [ 3588.153859] [] nfsd4_free_file_rcu+0x65/0x80 [nfsd] > > > [ 3588.153861] [] rcu_nocb_kthread+0x335/0x510 > > > [ 3588.153862] [] ? rcu_nocb_kthread+0x27f/0x510 > > > [ 3588.153863] [] ? rcu_cpu_notify+0x3e0/0x3e0 > > > [ 3588.153866] [] kthread+0x101/0x120 > > > [ 3588.153868] [] ? trace_hardirqs_on_caller+0xf4/0x1b0 > > > [ 3588.153871] [] ret_from_fork+0x1f/0x40 > > > [ 3588.153872] [] ? kthread_create_on_node+0x250/0x250 > > > > > > > > > release_all_access() seems to be doing correct job of all that cleaning, so > > > there must be some other path that I do not quite see. > > > > > > Hopefully you are more familiar with the code and can see the problem right away ;) > > Hmm...well I'm not seeing it right offhand, and haven't been able to > > reproduce the problem so far after a couple of attempts by hand. What > > sort of workload are you running before you see that warning pop? > Well, the workload is a crazed twisty conflicting operations set in a very limited > namespace (called racer.sh, > http://git.whamcloud.com/fs/lustrerelease.git/tree/refs/heads/master:/lustre/tests/racer ) > > It does all sorts of crazy unimaginable stuff that is hard to predict, and typically I > run it on several mountpoints all pointing to the same spot > (now 3-ways: one instance on direct mount point in ext4, one on nfs mount mounted as > mount -o nfs and one on mount -o nfs4). > It must be hitting some rare race or a race + operations combination that leads to > the leak. > > To reproduce I run it like this until it stops (and it usually stops in > 2 or 3 iterations, so it takes some time): > $ cat ~/stress.sh > #!/bin/bash > > set -x > > cd /home/green/git/lustre-release/lustre/tests/racer > dd if=/dev/zero of=/tmp/loop bs=1024k count=1024 > mkfs.ext4 /tmp/loop > service rpcbind start > mount none /var/lib/nfs -t tmpfs > touch /var/lib/nfs/etab > service nfs-mountd start > > while :; do > > mount /tmp/loop /mnt/lustre -o loop || exit 1 > mkdir /mnt/lustre/racer > service nfs-server start || exit 2 > mount localhost:/mnt/lustre /mnt/nfs -t nfs -o nolock || exit 3 > mount localhost:/ /mnt/nfs2 -t nfs4 || exit 4 > DURATION=3600 sh racer.sh /mnt/nfs/racer & > DURATION=3600 sh racer.sh /mnt/nfs2/racer & > DURATION=3600 sh racer.sh /mnt/lustre/racer & > wait %1 %2 %3 > umount /mnt/nfs || exit 5 > umount /mnt/nfs2 || exit 6 > service nfs-server stop || exit 7 > umount /mnt/lustre || exit 8 > e2fsck -n -f /tmp/loop || exit 9 > done > > Please ignore all the Lustre references, the test is generic, it's just I am running > off nfs-readonly-root setup, so want to reuse existing mountpoint locations, > there's no Lustre in picture here). > With all the other problems from before fixed, now it typically stops either for > this leak discussed here, or for this other problem in nfs4 I described here: > http://marc.info/?l=linux-nfs&m=146518324823160&w=2 Thanks. So it seems likely we're looking at a race of some sort then... So, the way this is supposed to work is that the stateids each hold a reference to the nfs4_file. They also take an fi_access reference for the open modes that they represent. This is how we know when it's OK to close one of the files in the fd[] slots. It might be interesting to also print out the fi_access counters if the slot hasn't been zeroed out if you feel up to it. I think though that the open upgrade accounting may be wrong. __nfs4_file_get_access does an unconditional atomic_inc, so if the client does a open for write and then opens again for read/write, then we may end up with too many write fi_access references taken. That said, this code is quite subtle. I'd need to look over it in more detail before I offer up any fixes. I'd also appreciate it if anyone else wants to sanity check my analysis there. -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html