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 ;)
>
> Bye,
> Oleg
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?
--
Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
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