Re: [RFC RESEND] serial: 8250: fix regression in 8250 uart driver

[Dinh Nguyen <dinguyen@kernel.org>]

Hi Andy,

On 08/17/2016 06:14 AM, Andy Shevchenko wrote:
> 
> I sent a v2 of the series for internal review, same you may found on
> [1]. If Heikki is okay to that I'll send it here.
> 
> [1] https://bitbucket.org/andy-shev/linux/branch/topic%2Fdw%2Fqrk
> 

I tested this branch on SoCFPGA hardware and encountered this error[1].
Doing a bisect led me to this commit[2].

Dinh


--------------------[1]------------------------------

[    5.907714] ttyS0 - failed to request DMA
[    5.921937] VFS: Mounted root (nfs filesystem) on device 0:13.
[    5.928732] devtmpfs: mounted
[    5.932504] Freeing unused kernel memory: 1024K (c0900000 - c0a00000)
[    6.004532] Unable to handle kernel NULL pointer dereference at
virtual address 0000000c
[    6.012619] pgd = ef670000
[    6.015321] [0000000c] *pgd=2ec0a831, *pte=00000000, *ppte=00000000
[    6.021609] Internal error: Oops: 17 [#1] SMP ARM
[    6.026301] Modules linked in:
[    6.029365] CPU: 1 PID: 1 Comm: init Not tainted
4.8.0-rc3-00063-g6ce52b1 #12
[    6.036476] Hardware name: Altera SOCFPGA
[    6.040476] task: ef4ac000 task.stack: ef4b0000
[    6.045007] PC is at _stop+0x4/0x254
[    6.048579] LR is at pl330_terminate_all+0x4c/0x1e4
[    6.053447] pc : [<c03c2e5c>]    lr : [<c03c30f8>]    psr: 60000093
[    6.053447] sp : ef4b1e88  ip : 00000000  fp : 0000a109
[    6.064890] r10: 00000000  r9 : ef7c7cc0  r8 : eedfaa94
[    6.070099] r7 : eed30410  r6 : eec2be0c  r5 : 60000013  r4 : eec2be70
[    6.076605] r3 : 00000002  r2 : 00000002  r1 : 00000000  r0 : 00000000
[    6.083113] Flags: nZCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM
Segment none
[    6.090318] Control: 10c5387d  Table: 2f67004a  DAC: 00000051
[    6.096046] Process init (pid: 1, stack limit = 0xef4b0218)
[    6.101603] Stack: (0xef4b1e88 to 0xef4b2000)
[    6.105953] 1e80:                   eec2be70 60000013 eec2be0c
eedfaa94 ef7c7cc0 c03c30f8
[    6.114112] 1ea0: ef4b1ea0 ef4b1ea0 eedfaa00 eed8c02c eec2be20
20000013 c0a66208 c03f2b44
[    6.122272] 1ec0: 00000001 00000000 c0a66208 c0a66208 c0a66324
20000013 c0a66208 eedfaa94
[    6.130432] 1ee0: ef7c7cc0 c03f041c eedfaa00 c0a66208 eedfaa8c
c03ea774 eedfaa00 ef7cec00
[    6.138592] 1f00: c0a66208 00000001 eedfaa94 c03eb9a4 ef7cec00
ef1a2930 00000000 ef41bd90
[    6.146751] 1f20: ef1a4440 c03d0790 00080040 00080060 00000000
00000000 00002710 ef7c7cc0
[    6.154911] 1f40: ef1a2930 00000000 ef41bd90 ef1a4440 00000008
ef7c7cc8 0000a109 c021b594
[    6.163071] 1f60: 00000000 00000000 ef4ac3d4 c0a532f8 00000000
ef4ac000 c0107884 ef4b0000
[    6.171231] 1f80: 00000000 c0138a14 ef4b0000 ef4b1fb0 c0107884
00000006 c0107884 c010b274
[    6.179390] 1fa0: 00015500 00000000 bea16c4c c0107714 00000000
00000800 00000045 0000c79c
[    6.187550] 1fc0: 00015500 00000000 bea16c4c 00000006 bea16bc0
00009c59 10000000 0000a109
[    6.195709] 1fe0: 00000000 bea16bb4 0000bf81 b6f6413c 40000010
00000002 00000c84 01000002
[    6.203878] [<c03c2e5c>] (_stop) from [<c03c30f8>]
(pl330_terminate_all+0x4c/0x1e4)
[    6.211526] [<c03c30f8>] (pl330_terminate_all) from [<c03f2b44>]
(serial8250_release_dma+0x30/0x1c8)
[    6.220640] [<c03f2b44>] (serial8250_release_dma) from [<c03f041c>]
(serial8250_do_shutdown+0x64/0x144)
[    6.230019] [<c03f041c>] (serial8250_do_shutdown) from [<c03ea774>]
(uart_shutdown+0xd0/0x104)
[    6.238614] [<c03ea774>] (uart_shutdown) from [<c03eb9a4>]
(uart_close+0x148/0x298)
[    6.246266] [<c03eb9a4>] (uart_close) from [<c03d0790>]
(tty_release+0xf0/0x4d4)
[    6.253658] [<c03d0790>] (tty_release) from [<c021b594>]
(__fput+0x80/0x1c8)
[    6.260694] [<c021b594>] (__fput) from [<c0138a14>]
(task_work_run+0xb8/0xe8)
[    6.267822] [<c0138a14>] (task_work_run) from [<c010b274>]
(do_work_pending+0x7c/0xa4)
[    6.275727] [<c010b274>] (do_work_pending) from [<c0107714>]
(slow_work_pending+0xc/0x20)
[    6.283888] Code: e8bd8070 e3a04000 eafffff9 e92d4370 (e590300c)
[    6.289963] ---[ end trace e214cd70660516e6 ]---
[    6.294806] Kernel panic - not syncing: Attempted to kill init!
exitcode=0x0000000b
[    6.294806]
[    6.303932] CPU0: stopping
[    6.306645] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G      D
4.8.0-rc3-00063-g6ce52b1 #12
[    6.315406] Hardware name: Altera SOCFPGA
[    6.319425] [<c010fef0>] (unwind_backtrace) from [<c010b8a4>]
(show_stack+0x10/0x14)
[    6.327159] [<c010b8a4>] (show_stack) from [<c037aa18>]
(dump_stack+0x84/0x98)
[    6.334372] [<c037aa18>] (dump_stack) from [<c010edb4>]
(handle_IPI+0x2a0/0x2bc)
[    6.341755] [<c010edb4>] (handle_IPI) from [<c01014cc>]
(gic_handle_irq+0x88/0x8c)
[    6.349310] [<c01014cc>] (gic_handle_irq) from [<c010c38c>]
(__irq_svc+0x6c/0x90)
[    6.356775] Exception stack(0xc0a01f50 to 0xc0a01f98)
[    6.361815] 1f40:                                     00000000
ef9cd368 0000153c c01184a0
[    6.369976] 1f60: c0a00000 c0a024a4 c0a023c0 c0a50390 c0a02454
00000001 c0a02454 00000000
[    6.378135] 1f80: 60000013 c0a01fa0 c01081a8 c01081ac 60000013 ffffffff
[    6.384734] [<c010c38c>] (__irq_svc) from [<c01081ac>]
(arch_cpu_idle+0x38/0x3c)
[    6.392127] [<c01081ac>] (arch_cpu_idle) from [<c0158cec>]
(cpu_startup_entry+0x204/0x25c)
[    6.400379] [<c0158cec>] (cpu_startup_entry) from [<c0900c60>]
(start_kernel+0x370/0x37c)
[    6.408542] ---[ end Kernel panic - not syncing: Attempted to kill
init! exitcode=0x0000000b
[    6.408542]


--------------------[2]----------------------------------
commit 60a0605738814ca8fa180cdfef20fcc2a32ec1ef
Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Date:   Mon Jun 13 12:17:03 2016 +0300

    serial: 8250: allow user to skip using of DMA channels

    Currently DMA mode is enforced if the certain driver has such
support. It prevents user to enforce PIO mode for RX, TX, or both.

    The new module parameters skip_rxdma and skip_txdma allow user to
choose between auto mode, which is current and default behaviour,
disable RX, TX, or both DMA channels without hacking a kernel.

    Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>