On Wed 06-07-16 18:07:18, Jeff Layton wrote: > On Wed, 2016-07-06 at 12:46 -0500, Seth Forshee wrote: > > We're seeing a hang when freezing a container with an nfs bind mount while > > running iozone. Two iozone processes were hung with this stack trace. > > > > [] schedule+0x35/0x80 > > [] schedule_preempt_disabled+0xe/0x10 > > [] __mutex_lock_slowpath+0xb9/0x130 > > [] mutex_lock+0x1f/0x30 > > [] do_unlinkat+0x12b/0x2d0 > > [] SyS_unlink+0x16/0x20 > > [] entry_SYSCALL_64_fastpath+0x16/0x71 > > > > This seems to be due to another iozone thread frozen during unlink with > > this stack trace: > > > > [] __refrigerator+0x7a/0x140 > > [] nfs4_handle_exception+0x118/0x130 [nfsv4] > > [] nfs4_proc_remove+0x7d/0xf0 [nfsv4] > > [] nfs_unlink+0x149/0x350 [nfs] > > [] vfs_unlink+0xf1/0x1a0 > > [] do_unlinkat+0x279/0x2d0 > > [] SyS_unlink+0x16/0x20 > > [] entry_SYSCALL_64_fastpath+0x16/0x71 > > > > Since nfs is allowing the thread to be frozen with the inode locked it's > > preventing other threads trying to lock the same inode from freezing. It > > seems like a bad idea for nfs to be doing this. > > > > Yeah, known problem. Not a simple one to fix though. Apart from alternative Dave was mentioning in other email, what is the point to use freezable wait from this path in the first place? nfs4_handle_exception does nfs4_wait_clnt_recover from the same path and that does wait_on_bit_action with TASK_KILLABLE so we are waiting in two different modes from the same path AFAICS. There do not seem to be other callers of nfs4_delay outside of nfs4_handle_exception. Sounds like something is not quite right here to me. If the nfs4_delay did regular wait then the freezing would fail as well but at least it would be clear who is the culrprit rather than having an indirect dependency. -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
