Hello Ming,
I am trying the ublk and it seems very exciting.
However, I encounter an issue when I remove a ublk device that is mounted or
in use.
In ublk_ctrl_del_dev(), shouldn’t we *not* wait if ublk_idr_freed() is false?
It seems to me that it is saner to return -EBUSY in such a case and let
userspace deal with the results.
For instance, if I run the following (using ubdsrv):
$ mkfs.ext4 /dev/ram0
$ ./ublk add -t loop -f /dev/ram0
$ sudo mount /dev/ublkb0 tmp
$ sudo ./ublk del -a
ublk_ctrl_del_dev() would not be done until the partition is unmounted, and you
can get a splat that is similar to the one below.
What do you say? Would you agree to change the behavior to return -EBUSY?
Thanks,
Nadav
[ 974.149938] INFO: task ublk:2250 blocked for more than 120 seconds.
[ 974.157786] Not tainted 6.1.0 #30
[ 974.162369] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 974.171417] task:ublk state:D stack:0 pid:2250 ppid:2249 flags:0x00004004
[ 974.181054] Call Trace:
[ 974.184097] <TASK>
[ 974.186726] __schedule+0x37e/0xe10
[ 974.190915] ? __this_cpu_preempt_check+0x13/0x20
[ 974.196463] ? lock_release+0x133/0x2a0
[ 974.201043] schedule+0x67/0xe0
[ 974.204846] ublk_ctrl_uring_cmd+0xf45/0x1110
[ 974.210016] ? lock_is_held_type+0xdd/0x130
[ 974.214990] ? var_wake_function+0x60/0x60
[ 974.219872] ? rcu_read_lock_sched_held+0x4f/0x80
[ 974.225443] io_uring_cmd+0x9a/0x130
[ 974.229743] ? io_uring_cmd_prep+0xf0/0xf0
[ 974.234638] io_issue_sqe+0xfe/0x340
[ 974.238946] io_submit_sqes+0x231/0x750
[ 974.243553] __x64_sys_io_uring_enter+0x22b/0x640
[ 974.249134] ? trace_hardirqs_on+0x3c/0xe0
[ 974.254042] do_syscall_64+0x35/0x80
[ 974.258361] entry_SYSCALL_64_after_hwframe+0x46/0xb0
[ 974.264335] RIP: 0033:0x7f1dc2958efd
[ 974.268657] RSP: 002b:00007ffdfd22d638 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa
[ 974.277471] RAX: ffffffffffffffda RBX: 00005592eabe7f60 RCX: 00007f1dc2958efd
[ 974.285800] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000004
[ 974.294139] RBP: 00005592eabe7f60 R08: 0000000000000000 R09: 0000000000000008
[ 974.302473] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 974.310811] R13: 0000000000000000 R14: 00000000ffffffff R15: 0000000000000000
[ 974.319168] </TASK>
[ 974.321982]
[ 974.321982] Showing all locks held in the system:
[ 974.329776] 1 lock held by rcu_tasks_kthre/12:
[ 974.335443] #0: ffffffff82f6e890 (rcu_tasks.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x2d/0x3f0
[ 974.346935] 1 lock held by rcu_tasks_rude_/13:
[ 974.352573] #0: ffffffff82f6e610 (rcu_tasks_rude.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x2d/0x3f0
[ 974.364522] 1 lock held by rcu_tasks_trace/14:
[ 974.370246] #0: ffffffff82f6e350 (rcu_tasks_trace.tasks_gp_mutex){+.+.}-{3:3}, at: rcu_tasks_one_gp+0x2d/0x3f0
[ 974.382331] 1 lock held by khungtaskd/310:
[ 974.387730] #0: ffffffff82f6f2a0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x23/0x17e
[ 974.398598] 5 locks held by kworker/8:1/330:
[ 974.404176] 1 lock held by systemd-journal/761:
[ 974.410003] 1 lock held by in:imklog/1390:
[ 974.415337] #0: ffff88810ead82e8 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0x45/0x50
[ 974.425284] 2 locks held by ublk/2250:
[ 974.430167] #0: ffff8881764e68a8 (&ctx->uring_lock){+.+.}-{3:3}, at: __x64_sys_io_uring_enter+0x21f/0x640
[ 974.441708] #1: ffffffff83106368 (ublk_ctl_mutex){+.+.}-{3:3}, at: ublk_ctrl_uring_cmd+0x6e4/0x1110
[ 974.452674]
[ 974.455090] =============================================
