Re: [PATCH] uart: Fix crash in uart_write and uart_put_char

[Tycho Andersen <tycho@tycho.ws>]

On Wed, Jan 16, 2019 at 10:28:07AM -0800, samir@embedur.com wrote:
> From: Samir Virmani <samir@embedur.com>
> 
> We were experiencing a crash similar to the one reported as part of
> commit:a5ba1d95e46e ("uart: fix race between uart_put_char() and
> uart_shutdown()") in our testbed as well. We continue to observe the same
> crash after integrating the commit a5ba1d95e46e ("uart: fix race between
> uart_put_char() and uart_shutdown()")
> 
> On reviewing the change, the port lock should be taken prior to checking for
> if (!circ->buf) in fn. __uart_put_char and other fns. that update the buffer
> uart_state->xmit.
> 
> Traceback:
> 
> [11/27/2018 06:24:32.4870] Unable to handle kernel NULL pointer dereference
>                            at virtual address 0000003b
> 
> [11/27/2018 06:24:32.4950] PC is at memcpy+0x48/0x180
> [11/27/2018 06:24:32.4950] LR is at uart_write+0x74/0x120
> [11/27/2018 06:24:32.4950] pc : [<ffffffc0002e6808>]
>                            lr : [<ffffffc0003747cc>] pstate: 000001c5
> [11/27/2018 06:24:32.4950] sp : ffffffc076433d30
> [11/27/2018 06:24:32.4950] x29: ffffffc076433d30 x28: 0000000000000140
> [11/27/2018 06:24:32.4950] x27: ffffffc0009b9d5e x26: ffffffc07ce36580
> [11/27/2018 06:24:32.4950] x25: 0000000000000000 x24: 0000000000000140
> [11/27/2018 06:24:32.4950] x23: ffffffc000891200 x22: ffffffc01fc34000
> [11/27/2018 06:24:32.4950] x21: 0000000000000fff x20: 0000000000000076
> [11/27/2018 06:24:32.4950] x19: 0000000000000076 x18: 0000000000000000
> [11/27/2018 06:24:32.4950] x17: 000000000047cf08 x16: ffffffc000099e68
> [11/27/2018 06:24:32.4950] x15: 0000000000000018 x14: 776d726966205948
> [11/27/2018 06:24:32.4950] x13: 50203a6c6974755f x12: 74647075205d3333
> [11/27/2018 06:24:32.4950] x11: 3a35323a36203831 x10: 30322f37322f3131
> [11/27/2018 06:24:32.4950] x9 : 5b205d303638342e x8 : 746164206f742070
> [11/27/2018 06:24:32.4950] x7 : 7520736920657261 x6 : 000000000000003b
> [11/27/2018 06:24:32.4950] x5 : 000000000000817a x4 : 0000000000000008
> [11/27/2018 06:24:32.4950] x3 : 2f37322f31312a5b x2 : 000000000000006e
> [11/27/2018 06:24:32.4950] x1 : ffffffc0009b9cf0 x0 : 000000000000003b
> 
> [11/27/2018 06:24:32.4950] CPU2: stopping
> [11/27/2018 06:24:32.4950] CPU: 2 PID: 0 Comm: swapper/2 Tainted: P      D    O    4.1.51 #3
> [11/27/2018 06:24:32.4950] Hardware name: Broadcom-v8A (DT)
> [11/27/2018 06:24:32.4950] Call trace:
> [11/27/2018 06:24:32.4950] [<ffffffc0000883b8>] dump_backtrace+0x0/0x150
> [11/27/2018 06:24:32.4950] [<ffffffc00008851c>] show_stack+0x14/0x20
> [11/27/2018 06:24:32.4950] [<ffffffc0005ee810>] dump_stack+0x90/0xb0
> [11/27/2018 06:24:32.4950] [<ffffffc00008e844>] handle_IPI+0x18c/0x1a0
> [11/27/2018 06:24:32.4950] [<ffffffc000080c68>] gic_handle_irq+0x88/0x90
> 
> Fixes: a5ba1d95e46e ("uart: fix race between uart_put_char() and
>                       uart_shutdown()")
> Signed-off-by: Samir Virmani <samir@embedur.com>
> Cc: Tycho Andersen <tycho@tycho.ws>

Acked-by: Tycho Andersen <tycho@tycho.ws>

Thanks,

Tycho