On Mon 12-03-18 23:56:05, Mikhail Gavrilov wrote:
[...]
> [ 355.531533] ============================================
> [ 355.531534] WARNING: possible recursive locking detected
> [ 355.531536] 4.16.0-rc1-amd-vega+ #6 Not tainted
> [ 355.531537] --------------------------------------------
> [ 355.531539] CPU 0/KVM/4034 is trying to acquire lock:
> [ 355.531540] (&mm->mmap_sem){++++}, at: [<0000000026cd8acd>] get_user_pages_unlocked+0xe0/0x1d0
> [ 355.531549]
> but task is already holding lock:
> [ 355.531550] (&mm->mmap_sem){++++}, at: [<000000000690373b>] get_user_pages_unlocked+0x5e/0x1d0
> [ 355.531554]
> other info that might help us debug this:
> [ 355.531555] Possible unsafe locking scenario:
>
> [ 355.531556] CPU0
> [ 355.531557] ----
> [ 355.531558] lock(&mm->mmap_sem);
> [ 355.531559] lock(&mm->mmap_sem);
> [ 355.531561]
> *** DEADLOCK ***
>
> [ 355.531562] May be due to missing lock nesting notation
>
> [ 355.531564] 3 locks held by CPU 0/KVM/4034:
> [ 355.531564] #0: (&vcpu->mutex){+.+.}, at: [<00000000230699e6>] kvm_vcpu_ioctl+0x81/0x6b0 [kvm]
> [ 355.531586] #1: (&kvm->srcu){....}, at: [<000000000a3cc9a1>] kvm_arch_vcpu_ioctl_run+0x752/0x1b90 [kvm]
> [ 355.531602] #2: (&mm->mmap_sem){++++}, at: [<000000000690373b>] get_user_pages_unlocked+0x5e/0x1d0
Is this lockdep report real or a false positive? Because many tasks are
failing to take a mmap_sem. Maybe the same one?
[...]
> [ 615.239436] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [ 615.239437] pidof D11816 5076 5071 0x00000000
> [ 615.239441] Call Trace:
> [ 615.239443] ? __schedule+0x2e9/0xba0
> [ 615.239446] ? rwsem_down_read_failed+0x147/0x190
> [ 615.239449] schedule+0x2f/0x90
> [ 615.239450] rwsem_down_read_failed+0x118/0x190
> [ 615.239455] ? call_rwsem_down_read_failed+0x14/0x30
> [ 615.239457] call_rwsem_down_read_failed+0x14/0x30
> [ 615.239460] ? proc_pid_cmdline_read+0xd2/0x4a0
> [ 615.239462] down_read+0x97/0xa0
> [ 615.239464] proc_pid_cmdline_read+0xd2/0x4a0
> [ 615.239467] ? lock_acquire+0x9f/0x200
> [ 615.239469] ? debug_check_no_obj_freed+0xda/0x244
> [ 615.239473] ? __vfs_read+0x36/0x170
> [ 615.239475] __vfs_read+0x36/0x170
> [ 615.239479] vfs_read+0x9e/0x150
> [ 615.239482] SyS_read+0x55/0xc0
> [ 615.239484] ? trace_hardirqs_off_thunk+0x1a/0x1c
> [ 615.239487] do_syscall_64+0x7a/0x220
> [ 615.239489] entry_SYSCALL_64_after_hwframe+0x26/0x9b
> [ 615.239491] RIP: 0033:0x7f4d5da16701
> [ 615.239492] RSP: 002b:00007ffd5200b188 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> [ 615.239494] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4d5da16701
> [ 615.239496] RDX: 00000000000007ff RSI: 00007ffd5200b1a0 RDI: 0000000000000004
> [ 615.239497] RBP: 0000000000000042 R08: 0000000000000007 R09: 00007f4d5e1825f4
> [ 615.239498] R10: 0000000000000000 R11: 0000000000000246 R12: 000055abb07f5980
> [ 615.239500] R13: 00007ffd5200b1a0 R14: 0000000000000004 R15: 0000000000000000
> [ 615.239505] INFO: lockdep is turned off.
> [ 639.815026] kworker/dying (149) used greatest stack depth: 10520 bytes left
--
Michal Hocko
SUSE Labs
