Re: NFS: What is this delay for?

[Idan Kedar <idank@tonian.com>]

On Fri, Aug 24, 2012 at 5:19 PM, Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> Hello.
>
> I noticed a strange delay when I was running a test program for
> http://serverfault.com/questions/235059/vfs-file-max-limit-1231582-reached .
>
> ---------- test program start ----------
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/file.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <errno.h>
>
> int main(int argc, char *argv[]) {
>         while (1) {
>                 struct flock lock = { };
>                 int fd = open("/mnt/file", O_CREAT | O_RDWR, 0600);
>                 lock.l_type = F_WRLCK;
>                 lock.l_whence = SEEK_SET;
>                 if (fcntl(fd, F_SETLK, &lock)) {
>                         int err = errno;
>                         fprintf(stderr, "Error %d\n", err);
>                         return 1;
>                 }
>                 close(fd);
>                 fprintf(stderr, ".");
>         }
> }
> ---------- test program end ----------
>
> When above program is executed after "service nfs start", above program sleeps
> for about 90-100 seconds at the first fcntl() attempt. But after once the first
> '.' is printed, above program never sleeps even after above program was
> re-executed.
>
> # cat /etc/exports
> /mountdir *(rw,all_squash,sync,fsid=0)
> # service nfs start
> # mount -t nfs 127.0.0.1:/mountdir /mnt/
> # time ./a.out
>
> sysrq on 3.6.0-rc2-00400-g23dcfa6 kernel shows:
>
> [  728.514014] a.out           S 00000000  5656  4400   3765 0x00000080
> [  728.514014]  d9a0dd7c 00000046 d9a0dcf0 00000000 00000001 dcf0aec8 00000023 00000000
> [  728.514014]  00000000 dcf0aa60 c17d2220 c17d2220 9fac0f21 000000a8 c17d2220 c17d2220
> [  728.514014]  9fa96cf7 000000a8 dcf0aa60 000000a8 9fac0995 dcf0aa60 00000000 00000000
> [  728.514014] Call Trace:
> [  728.514014]  [<c143fc55>] ? _raw_spin_unlock_irqrestore+0x35/0x60
> [  728.514014]  [<c143e45e>] schedule+0x1e/0x50
> [  728.514014]  [<c143c6ea>] schedule_timeout+0xea/0x170
> [  728.514014]  [<c1040a10>] ? lock_timer_base+0x50/0x50
> [  728.514014]  [<c11e1f27>] nlmclnt_call+0x97/0x1f0
> [  728.514014]  [<c1053210>] ? wake_up_bit+0x30/0x30
> [  728.514014]  [<c11e282e>] nlmclnt_proc+0x22e/0x6f0
> [  728.514014]  [<c1062e1e>] ? local_clock+0x4e/0x60
> [  728.514014]  [<c11a567a>] nfs3_proc_lock+0x1a/0x20
> [  728.514014]  [<c1196069>] do_setlk+0xc9/0xf0
> [  728.514014]  [<c11961b8>] nfs_lock+0x98/0x170
> [  728.514014]  [<c1196120>] ? nfs_flock+0x90/0x90
> [  728.514014]  [<c1122161>] vfs_lock_file+0x21/0x50
> [  728.514014]  [<c112227a>] do_lock_file_wait+0x4a/0xd0
> [  728.514014]  [<c10c7426>] ? might_fault+0x46/0xa0
> [  728.514014]  [<c1230304>] ? _copy_from_user+0x34/0x80
> [  728.514014]  [<c112278e>] fcntl_setlk+0xce/0x2c0
> [  728.514014]  [<c107ba3b>] ? trace_hardirqs_on+0xb/0x10
> [  728.514014]  [<c10f0b82>] do_fcntl+0x1e2/0x5f0
> [  728.514014]  [<c10f1013>] sys_fcntl64+0x83/0xd0
> [  728.514014]  [<c144048c>] sysenter_do_call+0x12/0x32
>
> Same result for CentOS 6.3's 2.6.32-279.5.1.el6.i686 kernel:
>
> a.out         S 00000286     0  1290   1160 0x00000080
>  df4d1aa0 00000086 e0d20aac 00000286 00000007 df57c24c dcd94544 0000ad6f
>  00000000 df8393c0 0000001e d1daf53c 0000001e c0b25680 c0b25680 df4d1d48
>  c0b25680 c0b21024 c0b25680 df4d1d48 de01e000 00000246 e0d25b24 e0d3dd88
> Call Trace:
>  [<e0d20aac>] ? xs_sendpages+0x1cc/0x240 [sunrpc]
>  [<e0d25b24>] ? rpc_wake_up_next+0xc4/0x180 [sunrpc]
>  [<c0440372>] ? __wake_up+0x42/0x60
>  [<e0d1cecb>] ? rpc_release_client+0x7b/0x90 [sunrpc]
>  [<c0466137>] ? lock_timer_base+0x27/0x50
>  [<c083d34c>] ? schedule_timeout+0x12c/0x250
>  [<c04e3591>] ? mempool_free+0x81/0x90
>  [<c0466210>] ? process_timeout+0x0/0x10
>  [<e0daf8a6>] ? nlmclnt_call+0xd6/0x290 [lockd]
>  [<c0476a10>] ? autoremove_wake_function+0x0/0x40
>  [<e0db0349>] ? nlmclnt_proc+0x219/0x760 [lockd]
>  [<c04769f3>] ? wake_up_bit+0x13/0x30
>  [<e0eeda0e>] ? do_setlk+0xbe/0xe0 [nfs]
>  [<e0eedbd3>] ? nfs_lock+0xb3/0x1b0 [nfs]
>  [<c053be35>] ? do_filp_open+0x635/0xb00
>  [<c051f102>] ? cache_alloc_refill+0x172/0x510
>  [<e0eedb20>] ? nfs_lock+0x0/0x1b0 [nfs]
>  [<c056e1d2>] ? vfs_lock_file+0x22/0x50
>  [<c056e2eb>] ? do_lock_file_wait+0x4b/0xd0
>  [<c056e64f>] ? fcntl_setlk+0xff/0x1e0
>  [<c053cf52>] ? do_fcntl+0x92/0x440
>  [<c04b14cc>] ? audit_syscall_entry+0x21c/0x240
>  [<c053d35a>] ? sys_fcntl64+0x5a/0xd0
>  [<c0409a9f>] ? sysenter_do_call+0x12/0x28
>
> I wonder what this sleeping period is for.
> --
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After the NFS server restarts it has a grace period of 90 seconds, for
recovery purposes. You can read about it online.
You can also look it up on the NFS 4.1 RFC 5661:
http://tools.ietf.org/rfcmarkup?doc=5661

-- 
idank