[PATCH] atmel_serial: fix spinlock lockup in RS485 code

Claudio Scordino
2011-12-15T08:47:53Z

Hi all.

We have encountered a spinlock lockup in the RS485 part of the atmel_serial driver.

Here is the trace:

[ 68.030000] BUG: spinlock lockup on CPU#0, dnp_master/244, c07e82c0
[ 68.040000] [<c002a790>] (unwind_backtrace+0x0/0xf0) from [<c012f8f0>] (do_raw_spin_lock+0x10c/0x148)
[ 68.050000] [<c012f8f0>] (do_raw_spin_lock+0x10c/0x148) from [<c015152c>] (atmel_tasklet_func+0x10/0x708)
[ 68.060000] [<c015152c>] (atmel_tasklet_func+0x10/0x708) from [<c003bfd4>] (tasklet_action+0x8c/0xf4)
[ 68.070000] [<c003bfd4>] (tasklet_action+0x8c/0xf4) from [<c003c630>] (__do_softirq+0xa4/0x180)
[ 68.080000] [<c003c630>] (__do_softirq+0xa4/0x180) from [<c003c764>] (irq_exit+0x58/0xb0)
[ 68.090000] [<c003c764>] (irq_exit+0x58/0xb0) from [<c0021084>] (asm_do_IRQ+0x84/0xa4)
[ 68.100000] [<c0021084>] (asm_do_IRQ+0x84/0xa4) from [<c002622c>] (__irq_svc+0x4c/0x98)
[ 68.110000] Exception stack(0xc341fdc8 to 0xc341fe10)
[ 68.110000] fdc0: c07e82c0 00000000 00000200 c4818000 c341fe10 c07e82c0
[ 68.120000] fde0: 00000000 c07e82c0 c38d3318 c341e000 bebcee00 010a0b60 c07e83fc c341fe10
[ 68.130000] fe00: c0151d54 c023d9c0 60000013 ffffffff
[ 68.140000] [<c002622c>] (__irq_svc+0x4c/0x98) from [<c023d9c0>] (_raw_spin_unlock+0x0/0x48)
[ 68.140000] [<c023d9c0>] (_raw_spin_unlock+0x0/0x48) from [<00000000>] ( (null))

The soft lockup occurs later

[ 126.750000] BUG: soft lockup - CPU#0 stuck for 61s! [dnp_master:244]
[ 126.750000] irq event stamp: 0
[ 126.750000] hardirqs last enabled at (0): [< (null)>] (null)
[ 126.750000] hardirqs last disabled at (0): [<c0035e30>] copy_process+0x308/0xe78
[ 126.750000] softirqs last enabled at (0): [<c0035e30>] copy_process+0x308/0xe78
[ 126.750000] softirqs last disabled at (0): [< (null)>] (null)

The following patch (already tested by Dave, who also reported the bug) fixes the problem.

Regards,