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Date: Fri, 25 Nov 2005 09:32:49 -0200
From: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
To: Aristeu Sergio Rozanski Filho <aris@cathedrallabs.org>
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Cc: linuxppc-embedded@ozlabs.org
Subject: Re: [PATCH] cpm_uart: fix xchar sending
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On Fri, Nov 25, 2005 at 12:38:51PM -0200, 'Aristeu Sergio Rozanski Filho' wrote:
> Hi,
> 	while using SCC as uart and as serial console at same time I got this:
> 
> [  138.214258] Oops: kernel access of bad area, sig: 11 [#1]
> [  138.218832] PREEMPT
> [  138.221021] NIP: C0105C48 LR: C0105E60 SP: C03D5D10 REGS: c03d5c60 TRAP: 0300    Not tainted
> [  138.229280] MSR: 00009032 EE: 1 PR: 0 FP: 0 ME: 1 IR/DR: 11
> [  138.234713] DAR: 00000000, DSISR: C0000000
> [  138.238745] TASK = c0349420[693] 'sh' THREAD: c03d4000
> [  138.243754] Last syscall: 6
> [  138.246402] GPR00: FEFFFFFF C03D5D10 C0349420 C01FB094 00000011 00000000 C1ECFBBC C01F24B0
> [  138.254602] GPR08: FF002820 00000000 FF0028C0 00000000 19133615 A0CBCD5E 02000300 00000000
> [  138.262804] GPR16: 00000000 01FF9E4C 00000000 7FA9A770 00000000 00000000 1003E2A8 00000000
> [  138.271003] GPR24: 100562F4 7F9B6EF4 C0210000 C02A5338 C01FB094 00000000 C01FB094 C1F14574
> [  138.279376] NIP [c0105c48] cpm_uart_tx_pump+0x4c/0x22c
> [  138.284419] LR [c0105e60] cpm_uart_start_tx+0x38/0xb0
> [  138.289361] Call trace:
> [  138.291762]  [c0105e60] cpm_uart_start_tx+0x38/0xb0
> [  138.296547]  [c010277c] uart_send_xchar+0x88/0x118
> [  138.301244]  [c01029a0] uart_unthrottle+0x6c/0x138
> [  138.305942]  [c00ece10] check_unthrottle+0x60/0x64
> [  138.310641]  [c00ecec4] reset_buffer_flags+0xb0/0x138
> [  138.315595]  [c00ecf64] n_tty_flush_buffer+0x18/0x78
> [  138.320465]  [c00e81b0] tty_ldisc_flush+0x64/0x7c
> [  138.325078]  [c010410c] uart_close+0xf0/0x2c8
> [  138.329348]  [c00e9c48] release_dev+0x724/0x8d4
> [  138.333790]  [c00e9e18] tty_release+0x20/0x3c
> [  138.338061]  [c006e544] __fput+0x178/0x1e0
> [  138.342076]  [c006c43c] filp_close+0x54/0xac
> [  138.346261]  [c0002d90] ret_from_syscall+0x0/0x44
> [  138.352386] note: sh[693] exited with preempt_count 2
> 
> a easy way to reproduce it is log into the system using ssh and do:
> 	cat >/dev/ttyCPM0
> then, switch to minicom and write some stuff on it back to ssh, a control C
> produce the oops
> 
> this happens because uart_close calls uart_shutdown which frees xmit.buf,
> currently used by xchar sending in cpm_uart_tx_pump(), which seems wrong.
> 
> the attached patch fixes the oops and also fixes xchar sending.

Looks good to me.