Message-ID: <CAKnSG-Y59120iFY34_KBih8COYVBGBsj8qMZ-WDXD6aLmVyn8Q@mail.gmail.com>
Date:	Fri, 20 Jun 2014 12:22:34 +0530
From:	Abhijit Lamsoge <abhijitelinux@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Arm Target System hangs on uart_open/uart_write

Hi All,
This problem is fixed.
By modifying driver code for setting driver->ports correctly, to the
one allocated for uart port in uart_register_function.
If this is not done, then once an FD for uart file is received, the
cleanup, work is put into BH for processing, and then it does not know
for which port it has to do the BH cleanup, which is done by system
workqueue under kernel thread.
So due to this the kernel hits a WARN_ON in workqueue.c at 1300~ and
system hangs and that's why the above trace.

Abhijit


On Fri, Jun 6, 2014 at 6:29 PM, Abhijit Lamsoge <abhijitelinux@...il.com> wrote:
> Hi All,
> I've ported my driver to Linux Kernel 3.8.13.
> Earlier it was working fine for 3.5.x Kernels.
> I register a uart device file for data transfer like "/dev/xyz"
> All the tty_ops for this UART driver are initialized to my own tty
> uart_open/read/write/close functions.
> Which are respectively called, when a sys_open comes on the above device file.
>
> However,
> the captured dmesg from "cat /proc/kmsg" shows all the correct prints
> from the driver, and data is also transferred.
> But the system "HANGS" giving the following message.
> ---------------------------------------------XX------------------------------------------------------------------------
> 181.350280] WARNING: at kernel/workqueue.c:1300 __queue_work+0x2c8/0x36c()
> <4>[  181.353851] Modules linked in:
> <4>[  181.355468] [<c001b3d0>] (unwind_backtrace+0x0/0xf0) from
> [<c0042830>] (warn_slowpath_common+0x4c/0x64)
> <4>[  181.360412] [<c0042830>] (warn_slowpath_common+0x4c/0x64) from
> [<c0042864>] (warn_slowpath_null+0x1c/0x24)
> <4>[  181.365447] [<c0042864>] (warn_slowpath_null+0x1c/0x24) from
> [<c00587ac>] (__queue_work+0x2c8/0x36c)
> <4>[  181.370178] [<c00587ac>] (__queue_work+0x2c8/0x36c) from
> [<c00588b0>] (queue_work_on+0x40/0x4c)
> <4>[  181.374694] [<c00588b0>] (queue_work_on+0x40/0x4c) from
> [<c025a5e8>] (n_tty_open+0xa4/0x124)
> <4>[  181.379028] [<c025a5e8>] (n_tty_open+0xa4/0x124) from
> [<c025c8d8>] (tty_ldisc_open+0x50/0x74)
> <4>[  181.383453] [<c025c8d8>] (tty_ldisc_open+0x50/0x74) from
> [<c025d02c>] (tty_ldisc_setup+0x18/0x68)
> <4>[  181.388092] [<c025d02c>] (tty_ldisc_setup+0x18/0x68) from
> [<c02567bc>] (tty_init_dev+0xe0/0x17c)
> <4>[  181.392639] [<c02567bc>] (tty_init_dev+0xe0/0x17c) from
> [<c0256fe0>] (tty_open+0x2b0/0x518)
> <4>[  181.396942] [<c0256fe0>] (tty_open+0x2b0/0x518) from
> [<c00d45b0>] (chrdev_open+0x100/0x17c)
> <4>[  181.401245] [<c00d45b0>] (chrdev_open+0x100/0x17c) from
> [<c00cee7c>] (do_dentry_open+0x1d4/0x284)
> <4>[  181.405853] [<c00cee7c>] (do_dentry_open+0x1d4/0x284) from
> [<c00cef64>] (finish_open+0x38/0x4c)
> <4>[  181.410400] [<c00cef64>] (finish_open+0x38/0x4c) from
> [<c00dd1f0>] (do_last.isra.19+0x974/0xb98)
> <4>[  181.414916] [<c00dd1f0>] (do_last.isra.19+0x974/0xb98) from
> [<c00dd4bc>] (path_openat+0xa8/0x47c)
> <4>[  181.419464] [<c00dd4bc>] (path_openat+0xa8/0x47c) from
> [<c00ddb4c>] (do_filp_open+0x2c/0x78)
> <4>[  181.423797] [<c00ddb4c>] (do_filp_open+0x2c/0x78) from
> [<c00cffd4>] (do_sys_open+0xe4/0x174)
> <4>[  181.428131] [<c00cffd4>] (do_sys_open+0xe4/0x174) from
> [<c0013e00>] (ret_fast_syscall+0x0/0x30)
> <4>[  181.432586] ---[ end trace d39416ed62ef112f ]---
>
>
> ------------------More stuff------------------------------
>
> [  218.371063] INFO: rcu_preempt detected stalls on CPUs/tasks: { 0}
> (detected by 1, t=2690 jiffies, g=1881, c=1880, q=87)
> [  218.376617] Backtrace for cpu 1 (current):
> [  218.378753] [<c001b3d0>] (unwind_backtrace+0x0/0xf0) from
> [<c0019304>] (smp_send_all_cpu_backtrace+0x58/0xcc)
> [  218.383850] [<c0019304>] (smp_send_all_cpu_backtrace+0x58/0xcc)
> from [<c0094fac>] (rcu_check_callbacks+0x574/0x730)
> [  218.389190] [<c0094fac>] (rcu_check_callbacks+0x574/0x730) from
> [<c004f12c>] (update_process_times+0x3c/0x6c)
> [  218.394287] [<c004f12c>] (update_process_times+0x3c/0x6c) from
> [<c007eabc>] (tick_sched_timer+0x58/0x8c)
> [  218.399139] [<c007eabc>] (tick_sched_timer+0x58/0x8c) from
> [<c00620c8>] (__run_hrtimer.isra.16+0x50/0xd0)
> [  218.404052] [<c00620c8>] (__run_hrtimer.isra.16+0x50/0xd0) from
> [<c0062a68>] (hrtimer_interrupt+0x140/0x2a0)
> [  218.409088] [<c0062a68>] (hrtimer_interrupt+0x140/0x2a0) from
> [<c0019e34>] (arch_timer_handler_phys+0x2c/0x3c)
> [  218.414215] [<c0019e34>] (arch_timer_handler_phys+0x2c/0x3c) from
> [<c008f984>] (handle_percpu_devid_irq+0x80/0xa0)
> [  218.419525] [<c008f984>] (handle_percpu_devid_irq+0x80/0xa0) from
> [<c008c448>] (generic_handle_irq+0x20/0x30)
> [  218.424621] [<c008c448>] (generic_handle_irq+0x20/0x30) from
> [<c0014d5c>] (handle_IRQ+0x7c/0xac)
> [  218.429138] [<c0014d5c>] (handle_IRQ+0x7c/0xac) from [<c000849c>]
> (gic_handle_irq+0x3c/0x5c)
> [  218.433441] [<c000849c>] (gic_handle_irq+0x3c/0x5c) from
> [<c0013980>] (__irq_svc+0x40/0x74)
> [  218.437744] Exception stack(0xeab87dd0 to 0xeab87e18)
> [  218.440338] 7dc0:                                     00000002
> 00000002 00000000 00000001
> [  218.444519] 7de0: eab87e3c c1395b80 c1395b80 c1395b88 00c8f000
> 00000001 00000000 00000000
> [  218.448699] 7e00: 00000001 eab87e18 c0025458 c0082e68 20000113 ffffffff
> [  218.452117] [<c0013980>] (__irq_svc+0x40/0x74) from [<c0082e68>]
> (generic_exec_single+0x7c/0x94)
> [  218.456634] [<c0082e68>] (generic_exec_single+0x7c/0x94) from
> [<c0082fd4>] (smp_call_function_single+0x154/0x1d8)
> [  218.461883] [<c0082fd4>] (smp_call_function_single+0x154/0x1d8)
> from [<c0083480>] (smp_call_function+0x34/0x64)
> [  218.467041] [<c0083480>] (smp_call_function+0x34/0x64) from
> [<c0019ba4>] (flush_tlb_kernel_range+0x50/0x60)
> [  218.472045] [<c0019ba4>] (flush_tlb_kernel_range+0x50/0x60) from
> [<c0393f9c>] (binder_deferred_func+0x4ac/0x5f8)
> [  218.477294] [<c0393f9c>] (binder_deferred_func+0x4ac/0x5f8) from
> [<c00577f8>] (process_one_work+0x260/0x408)
> [  218.482330] [<c00577f8>] (process_one_work+0x260/0x408) from
> [<c0058050>] (worker_thread+0x2c8/0x428)
> [  218.487060] [<c0058050>] (worker_thread+0x2c8/0x428) from
> [<c005e418>] (kthread+0xa0/0xac)
> [  218.491302] [<c005e418>] (kthread+0xa0/0xac) from [<c0013e98>]
> (ret_from_fork+0x14/0x3c)
> [  218.495452]
> [  218.495452] sending IPI to all other CPUs:
>
> ----------------------Ends here-------------------------------
>
> I am not sure, whether it's a problem of hardware, as when the kthread
> schedules the work on CPU #1 for ARM.
> There is no "unable to handle" message.
> I am not am expert on how kernel internally handles workqueues and
> schedules/puts them on the processor.
>
> Any pointers in this regard are welcome.
>
> -- Abhijit
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