On Thu, 19 Mar 2015 17:59:15 -0700 Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > On Jan 14, 2015, at 10:32 AM, Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx> wrote: > > > On Wed, 14 Jan 2015 13:06:17 -0500 > > Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > > > >> On Wed, Jan 14, 2015 at 12:27 PM, Jeff Layton > >> <jeff.layton@xxxxxxxxxxxxxxx> wrote: > >>> On Wed, 14 Jan 2015 12:13:43 -0500 > >>> Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote: > >>> > >>>> On Wed, Jan 14, 2015 at 10:32 AM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote: > >>>>> Bruce reported seeing this warning pop when mounting using v4.1: > >>>>> > >>>>> ------------[ cut here ]------------ > >>>>> WARNING: CPU: 1 PID: 1121 at kernel/sched/core.c:7300 __might_sleep+0xbd/0xd0() > >>>>> do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffff810ff58f>] prepare_to_wait+0x2f/0x90 > >>>>> Modules linked in: rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace sunrpc fscache ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_pcm snd_timer ppdev joydev snd virtio_console virtio_balloon pcspkr serio_raw parport_pc parport pvpanic floppy soundcore i2c_piix4 virtio_blk virtio_net qxl drm_kms_helper ttm drm virtio_pci virtio_ring ata_generic virtio pata_acpi > >>>>> CPU: 1 PID: 1121 Comm: nfsv4.1-svc Not tainted 3.19.0-rc4+ #25 > >>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140709_153950- 04/01/2014 > >>>>> 0000000000000000 000000004e5e3f73 ffff8800b998fb48 ffffffff8186ac78 > >>>>> 0000000000000000 ffff8800b998fba0 ffff8800b998fb88 ffffffff810ac9da > >>>>> ffff8800b998fb68 ffffffff81c923e7 00000000000004d9 0000000000000000 > >>>>> Call Trace: > >>>>> [<ffffffff8186ac78>] dump_stack+0x4c/0x65 > >>>>> [<ffffffff810ac9da>] warn_slowpath_common+0x8a/0xc0 > >>>>> [<ffffffff810aca65>] warn_slowpath_fmt+0x55/0x70 > >>>>> [<ffffffff810ff58f>] ? prepare_to_wait+0x2f/0x90 > >>>>> [<ffffffff810ff58f>] ? prepare_to_wait+0x2f/0x90 > >>>>> [<ffffffff810dd2ad>] __might_sleep+0xbd/0xd0 > >>>>> [<ffffffff8124c973>] kmem_cache_alloc_trace+0x243/0x430 > >>>>> [<ffffffff810d941e>] ? groups_alloc+0x3e/0x130 > >>>>> [<ffffffff810d941e>] groups_alloc+0x3e/0x130 > >>>>> [<ffffffffa0301b1e>] svcauth_unix_accept+0x16e/0x290 [sunrpc] > >>>>> [<ffffffffa0300571>] svc_authenticate+0xe1/0xf0 [sunrpc] > >>>>> [<ffffffffa02fc564>] svc_process_common+0x244/0x6a0 [sunrpc] > >>>>> [<ffffffffa02fd044>] bc_svc_process+0x1c4/0x260 [sunrpc] > >>>>> [<ffffffffa03d5478>] nfs41_callback_svc+0x128/0x1f0 [nfsv4] > >>>>> [<ffffffff810ff970>] ? wait_woken+0xc0/0xc0 > >>>>> [<ffffffffa03d5350>] ? nfs4_callback_svc+0x60/0x60 [nfsv4] > >>>>> [<ffffffff810d45bf>] kthread+0x11f/0x140 > >>>>> [<ffffffff810ea815>] ? local_clock+0x15/0x30 > >>>>> [<ffffffff810d44a0>] ? kthread_create_on_node+0x250/0x250 > >>>>> [<ffffffff81874bfc>] ret_from_fork+0x7c/0xb0 > >>>>> [<ffffffff810d44a0>] ? kthread_create_on_node+0x250/0x250 > >>>>> ---[ end trace 675220a11e30f4f2 ]--- > >>>>> > >>>>> nfs41_callback_svc does most of its work while in TASK_INTERRUPTIBLE, > >>>>> which is just wrong. Fix that by finishing the wait immediately if we've > >>>>> found that the list has something on it. > >>>> > >>>> ACK. > >>>> > >>>>> Also, we don't expect this kthread to accept signals, so we should be > >>>>> using a TASK_UNINTERRUPTIBLE sleep instead. > >>>> > >>>> Umm... Won't that end up triggering the hung task watchdog for every > >>>> 120seconds with no callback activity? > >>>> > >>> > >>> Doh! You're correct. > >>> > >>> What's the right way to do this then? Do we need to use > >>> schedule_timeout and wake up every 100s or so? Using TASK_INTERRUPTIBLE > >>> to work around the watchdog seems wrong but I guess we can live with > >>> that in the short term if it's the only way. > >> > >> The alternative is to use TASK_KILLABLE. That's a little more > >> restrictive, but still a PITA. Note the both TASK_INTERRUPTIBLE and > >> TASK_KILLABLE will need something to handle that signalled() case, > >> otherwise we end up with a permanent busy-waiting loop. > >> > > > > Heh, our emails appear to have crossed. I went with a schedule_timeout > > for v2 so we can sidestep the whole issue of signals. > > > > It's simple enough to add a flush_signals() call at the end of the > > loop, but I'm a little leery of what effects we might see if the thread > > catches a signal while in the middle of doing real work. > > > > If you really think that's the better approach, I can do a v3 patch > > that does that however. > > After applying this patch to a 3.19.0 test system, the WARNINGS are > gone, but the system load average is pinned at 1.00. > > root 12105 0.1 0.0 0 0 ? D Mar18 1:19 [nfsv4.1-svc] > Darn, good point... I forgot about the stupid load avg on Linux counting D state tasks toward the load avg (why, oh why...). I guess we will have to use a different task state after all -- probably TASK_KILLABLE and just try to ignore fatal signals as best we can. I'll plan to do that when I get a minute. Suggestions of better ways to do this would be appreciated though. Cheers, -- 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
