commit 73ac5d6a "arm/syscalls: Check address limit on user-mode return" breaks NFS boot on i.MX6 platforms

[Thomas Garnier]

On Tue, Aug 29, 2017 at 7:27 AM, Lothar Waßmann <LW at karo-electronics.de> wrote:
>
> Hi,
>
> I found that I cannot boot a 4.13-rc7 (next-20170829) kernel on a TX6Q
> module. With NFS root the kernel works well until it starts the init
> process and then is busy making NFS calls over the network, but doesn't
> seem to proceed any further. It reacts to sysrq triggers.

We got report of a similar bugs few weeks ago. I have a change queued
waiting for Russel approval. I will CC you to this thread.

>
> I bisected it down to commit 73ac5d6a ("arm/syscalls: Check address
> limit on user-mode return").
> When reverting this commit on top of next-20170829 everything works
> well again, though there is a deadlock reported by lockdep:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.13.0-rc7-next-20170829-karo-00001-ge6888ab #46 Not tainted
> ------------------------------------------------------
> kworker/0:1H/1035 is trying to acquire lock:
>  ((&task->u.tk_work)){+.+.}, at: [<80136264>] process_one_work+0x128/0x42c
>
> but task is already holding lock:
>  ("xprtiod"){+.+.}, at: [<80136264>] process_one_work+0x128/0x42c
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 ("xprtiod"){+.+.}:
>        flush_work+0x1b0/0x248
>        __cancel_work_timer+0x108/0x1e0
>        xs_destroy+0x34/0x50
>        __rpc_execute+0x94/0x26c
>        process_one_work+0x1a4/0x42c
>        worker_thread+0x38/0x4d4
>        kthread+0x138/0x170
>        ret_from_fork+0x14/0x24
>
> -> #0 ((&task->u.tk_work)){+.+.}:
>        lock_acquire+0x70/0x90
>        process_one_work+0x18c/0x42c
>        worker_thread+0x38/0x4d4
>        kthread+0x138/0x170
>        ret_from_fork+0x14/0x24
>
> other info that might help us debug this:
>
>  Possible unsafe locking scenario:
>
>        CPU0                    CPU1
>        ----                    ----
>   lock("xprtiod");
>                                lock((&task->u.tk_work));
>                                lock("xprtiod");
>   lock((&task->u.tk_work));
>
>  *** DEADLOCK ***
>
> 1 lock held by kworker/0:1H/1035:
>  #0:  ("xprtiod"){+.+.}, at: [<80136264>] process_one_work+0x128/0x42c
>
> stack backtrace:
> CPU: 0 PID: 1035 Comm: kworker/0:1H Not tainted 4.13.0-rc7-next-20170829-karo-00001-ge6888ab #46
> Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> Workqueue: xprtiod rpc_async_schedule
> [<801100cc>] (unwind_backtrace) from [<8010bcb8>] (show_stack+0x10/0x14)
> [<8010bcb8>] (show_stack) from [<80739af4>] (dump_stack+0xb8/0xe4)
> [<80739af4>] (dump_stack) from [<80161108>] (print_circular_bug+0x258/0x414)
> [<80161108>] (print_circular_bug) from [<80162330>] (check_prev_add+0x44c/0x910)
> [<80162330>] (check_prev_add) from [<801653ac>] (__lock_acquire+0x1488/0x15ec)
> [<801653ac>] (__lock_acquire) from [<80165d60>] (lock_acquire+0x70/0x90)
> [<80165d60>] (lock_acquire) from [<801362c8>] (process_one_work+0x18c/0x42c)
> [<801362c8>] (process_one_work) from [<801365a0>] (worker_thread+0x38/0x4d4)
> [<801365a0>] (worker_thread) from [<8013c8b4>] (kthread+0x138/0x170)
> [<8013c8b4>] (kthread) from [<80107b30>] (ret_from_fork+0x14/0x24)
> Executing /sbin/init
>
>
>
> Lothar Waßmann




-- 
Thomas