On Fri, Jul 08, 2016 at 09:53:30AM +1000, Dave Chinner wrote: > On Wed, Jul 06, 2016 at 06:07:18PM -0400, 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. > > Actually, it is simple to fix. > > <insert broken record about suspend should be using freeze_super(), > not sys_sync(), to suspend filesystem operations> > > i.e. the VFS blocks new operations from starting, and then then the > NFS client simply needs to implement ->freeze_fs to drain all it's > active operations before returning. Problem solved. No, this won't solve my problem. We're not doing a full suspend, rather using a freezer cgroup to freeze a subset of processes. We don't want to want to fully freeze the filesystem. Thanks, Seth -- 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
