Hi, I recently submitted an NFS bug (https://bugzilla.kernel.org/show_bug.cgi?id=201655) where nfsd randomly locks up on rwsem_down_write_failed: Nov 10 15:29:55 rem kernel: INFO: task nfsd:7464 blocked for more than 120 seconds. Nov 10 15:29:55 rem kernel: Tainted: P O 4.19.1 #1-NixOS Nov 10 15:29:55 rem kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Nov 10 15:29:55 rem kernel: nfsd D 0 7464 2 0x80000000 Nov 10 15:29:55 rem kernel: Call Trace: Nov 10 15:29:55 rem kernel: ? __schedule+0x1d3/0x6f0 Nov 10 15:29:55 rem kernel: schedule+0x28/0x80 Nov 10 15:29:55 rem kernel: rwsem_down_write_failed+0x15e/0x350 Nov 10 15:29:55 rem kernel: ? call_rwsem_down_write_failed+0x13/0x20 Nov 10 15:29:55 rem kernel: call_rwsem_down_write_failed+0x13/0x20 Nov 10 15:29:55 rem kernel: down_write+0x29/0x40 Nov 10 15:29:55 rem kernel: ext4_file_write_iter+0x91/0x3d0 [ext4] Nov 10 15:29:55 rem kernel: ? nfsd_proc_write+0x160/0x160 [nfsd] Nov 10 15:29:55 rem kernel: ? exportfs_decode_fh+0xf2/0x2b0 ... (more details in the bugzilla) And according to Bruce Fields: > I'm guessing it's the inode_lock at the start of ext4_file_write_iter that's blocking. On a quick look I don't see any of the callers taking any locks. So I'd expect that elsewhere there'd be a process holding that inode lock and blocking on something else. > > Based just on this might first guess would be a vfs or maybe ext4 bug rather than an nfsd bug, but I'm not seeing how to reassign. May be worth reporting to the relevant mailing lists. So, starting with ext4, I was wondering if you had an idea of what the cause might be or where the fault truly lies. Kevin Liu
