Converting a device driver for a real time kernel

aleggo · 02-09-2010, 04:29 AM

Hello,

What is the best way of converting an existing device driver to work under a real-time kernel?

A device driver provided for a special serial card (Curtiss Wright SL240 sFDFP card http://www.cwcembedded.com/products/0/1/461.html) works under vanilla Linux (SLES SP10 SP2 kernel 2.6.16.60-0.21-smp), but compiling the driver under the real time kernel (2.6.22.19-0.14-rt) the system locks up and crashes. The rt kernel is being used to write large amounts of data from the serial card to disk and testing has found the rt kernel has the best consistent write performance.

I have gone back to the supplier and they are not interested in developing a real time version of the driver. So I am trying to modify the driver myself. The driver code can be provided if anyone wants a look.

Any assistance would be useful.

aleggo · 02-11-2010, 08:37 AM

I have uploaded the driver code, if anyone wants a look:
http://dl.dropbox.com/u/4618054/nsl_driver.zip

Using the existing RT kernel, I have enabled debugging in the driver and the crash output from dmesg is below.

START dmesg dump

GTDBG: dcfiIoctl()
GTDBG: <4>dcfiIoctlXfer begin
GTDBG: dcfiXferChunk() begin
GTDBG: dcfiXferChunk() end
GTDBG: <4>dcfiIoctlXfer end
GTDBG: dcfiIoctl() exit...
GTDBG: dcfiIoctl()
GTDBG: <4>dcfiIoctlXfer begin
stopped custom tracer.
Unable to handle kernel NULL pointer dereference at 0000000000000028 RIP:
<6>GTDBG: dcfiXferChunk() end
[<ffffffff80255b58>] lock_hrtimer_base+0x18/0x60 PGD 5848c7067 PUD 584d19067 PMD 0
Oops: 0000 [1] PREEMPT SMP
last sysfs file: /devices/pci0000:00/0000:00:00.0/irq
CPU 1
Modules linked in: dcfi_nsl_module nfsd exportfs lockd nfs_acl sunrpc ipv6 button sg battery ac st apparmor<6>GTDBG: <4>dcfiIoctlXfer end xfs loop dm_mod usbhid hid ff_memless generic nx_nic ide_core ipmi_si uhci_hcd ehci_hcd usbcore ipmi_msghandler firmware_class rtc_cmos rtc_core rtc_lib reiserfs edd fan thermal processor cciss ata_piix libata sd_mod scsi_mod
Pid: 7023, comm: nsltp Tainted: G N 2.6.22.19-0.14-rt #1
RIP: 0010:[<ffffffff80255b58>] [<ffffffff80255b58>] lock_hrtimer_base+0x18/0x60
RSP: 0018:ffff81057d9afb38 EFLAGS: 00010292
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff810308c50b30
RDX: ffff81058c080040 RSI: ffff81057d9afb68 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff81057d9ae000 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8021cec0 R12: ffff81057d9afb68
R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000292
FS: 0000000041001940(0063) GS:ffff81059762e5c0(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000028 CR3: 000000058d250000 CR4: 00000000000006e0 Process nsltp (pid: 7023, threadinfo ffff81057d9ae000, task ffff81058c080040)
Stack: 0000000000000000 00000000ffffffff 0000000000000004 ffffffff80255c08
0000000000000004 ffffffff8025e97d 0000000000400040 0000000000000000<6>GTDBG: dcfiIoctl() exit...

ffff810308c50b08 ffffffff80255c76 0000000000000000 ffffffff80468cd2 Call Trace:
GTDBG: dcfiXferChunk() end
GTDBG: <4>dcfiIoctlXfer end
GTDBG: dcfiIoctl() exit...
[<ffffffff80255c08>] hrtimer_try_to_cancel+0x18/0x70
GTDBG: dcfiIoctl()
[<ffffffff8025e97d>] do_try_to_take_rt_mutex+0x16d/0x1b0
[<ffffffff80255c76>] hrtimer_cancel+0x16/0x20
GTDBG: <4>dcfiIoctlXfer begin
GTDBG: dcfiXferChunk() begin
[<ffffffff80468cd2>] rt_mutex_slowlock+0x242/0x2d8 [<ffffffff8025f4fd>] rt_down+0x1d/0x60 [<ffffffff8843c5cd>] :dcfi_nsl_module:dcfiIoctlXfer+0x4bd/0x6a0
GTDBG: dcfiIoctl()
GTDBG: <4>dcfiIoctlXfer begin
GTDBG: dcfiXferChunk() begin
[<ffffffff8843c965>] :dcfi_nsl_module:dcfiIoctl+0x1b5/0x440
[<ffffffff8025e97d>] do_try_to_take_rt_mutex+0x16d/0x1b0
[<ffffffff80468c26>] rt_mutex_slowlock+0x196/0x2d8 [<ffffffff8843c7b0>] :dcfi_nsl_module:dcfiIoctl+0x0/0x440
[<ffffffff802bb8b3>] do_ioctl+0x93/0xe0 [<ffffffff802bb974>] vfs_ioctl+0x74/0x2d0 [<ffffffff802bbc65>] sys_ioctl+0x95/0xb0 [<ffffffff8020a04e>] system_call+0x7e/0x83

Code: 48 8b 5d 28 48 85 db 74 33 48 8b 3b e8 87 3b 21 00 49 89 04 RIP [<ffffffff80255b58>] lock_hrtimer_base+0x18/0x60 RSP <ffff81057d9afb38>
CR2: 0000000000000028
GTDBG: dcfiXferChunk() end
GTDBG: <4>dcfiIoctlXfer end
GTDBG: dcfiIoctl() exit...
GTDBG: dcfiXferChunk() end
GTDBG: <4>dcfiIoctlXfer end
GTDBG: dcfiIoctl() exit...

END dmesg dump

fslateef · 02-26-2010, 09:38 AM

Quote:

Originally Posted by aleggo

Hello,

What is the best way of converting an existing device driver to work under a real-time kernel?

A device driver provided for a special serial card (Curtiss Wright SL240 sFDFP card http://www.cwcembedded.com/products/0/1/461.html) works under vanilla Linux (SLES SP10 SP2 kernel 2.6.16.60-0.21-smp), but compiling the driver under the real time kernel (2.6.22.19-0.14-rt) the system locks up and crashes. The rt kernel is being used to write large amounts of data from the serial card to disk and testing has found the rt kernel has the best consistent write performance.

I have gone back to the supplier and they are not interested in developing a real time version of the driver. So I am trying to modify the driver myself. The driver code can be provided if anyone wants a look.

Any assistance would be useful.

Can you please tell which RT Linux you are using ? RTAI, Xenomai or other ? And are you have some other modules/applications which needs RT ?