So plugging in a device on USB with BFQ as scheduler now works without hiccup (probably thanks to Ming Lei's last patch), but of course I found another problem. Unmounting the device after use, changing the scheduler back to deadline or kyber and rmmod'ing the BFQ module reproducibly gives me: kernel: ============================================================================= kernel: BUG bfq_queue (Tainted: G B ): Objects remaining in bfq_queue on __kmem_cache_shutdown() kernel: ----------------------------------------------------------------------------- kernel: kernel: INFO: Slab 0xffffea001601fc00 objects=37 used=3 fp=0xffff8805807f0360 flags=0x8000000000008100 kernel: CPU: 0 PID: 9967 Comm: rmmod Tainted: G B 4.14.5 #1 kernel: Hardware name: Gigabyte Technology Co., Ltd. P67-DS3-B3/P67-DS3-B3, BIOS F1 05/06/2011 kernel: Call Trace: kernel: dump_stack+0x46/0x5e kernel: slab_err+0x9e/0xb0 kernel: ? on_each_cpu_mask+0x35/0x40 kernel: ? ksm_migrate_page+0x60/0x60 kernel: ? __kmalloc+0x1c9/0x1d0 kernel: __kmem_cache_shutdown+0x177/0x350 kernel: shutdown_cache+0xf/0x130 kernel: kmem_cache_destroy+0x19e/0x1b0 kernel: SyS_delete_module+0x168/0x230 kernel: ? exit_to_usermode_loop+0x39/0x80 kernel: entry_SYSCALL_64_fastpath+0x13/0x94 kernel: RIP: 0033:0x7f53e4136b97 kernel: RSP: 002b:00007ffd660061d8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0 kernel: RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f53e4136b97 kernel: RDX: 000000000000000a RSI: 0000000000000800 RDI: 00000000006247f8 kernel: RBP: 0000000000000000 R08: 00007ffd66005171 R09: 0000000000000000 kernel: R10: 00007f53e41acbc0 R11: 0000000000000206 R12: 0000000000624790 kernel: R13: 00007ffd660051d0 R14: 0000000000624790 R15: 0000000000623260 kernel: INFO: Object 0xffff8805807f0000 @offset=0 kernel: INFO: Object 0xffff8805807f01b0 @offset=432 kernel: INFO: Object 0xffff8805807f3cc0 @offset=15552 kernel: kmem_cache_destroy bfq_queue: Slab cache still has objects kernel: CPU: 0 PID: 9967 Comm: rmmod Tainted: G B 4.14.5 #1 kernel: Hardware name: Gigabyte Technology Co., Ltd. P67-DS3-B3/P67-DS3-B3, BIOS F1 05/06/2011 kernel: Call Trace: kernel: dump_stack+0x46/0x5e kernel: kmem_cache_destroy+0x191/0x1b0 kernel: SyS_delete_module+0x168/0x230 kernel: ? exit_to_usermode_loop+0x39/0x80 kernel: entry_SYSCALL_64_fastpath+0x13/0x94 kernel: RIP: 0033:0x7f53e4136b97 kernel: RSP: 002b:00007ffd660061d8 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0 kernel: RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f53e4136b97 kernel: RDX: 000000000000000a RSI: 0000000000000800 RDI: 00000000006247f8 kernel: RBP: 0000000000000000 R08: 00007ffd66005171 R09: 0000000000000000 kernel: R10: 00007f53e41acbc0 R11: 0000000000000206 R12: 0000000000624790 kernel: R13: 00007ffd660051d0 R14: 0000000000624790 R15: 0000000000623260 Unloading e.g. kyber repeatably works fine, so I assume this is a bug. :) I'm running 4.14.5 (currently in -rc1) + block/scsi picked from 4.15-git and the list. Would be good to know if someone can reproduce it. thanks, Holger
