答复: [PATCH] TTY: serial_core, add ->install

["Li,Rongqing" <lirongqing@baidu.com>]

> -----邮件原件-----
> 发件人: linux-kernel-owner@vger.kernel.org
> [mailto:linux-kernel-owner@vger.kernel.org] 代表 Jiri Slaby
> 发送时间: 2019年4月17日 16:59
> 收件人: gregkh@linuxfoundation.org
> 抄送: linux-serial@vger.kernel.org; linux-kernel@vger.kernel.org; Jiri Slaby
> <jslaby@suse.cz>; Li,Rongqing <lirongqing@baidu.com>; Wang,Li(ACG Cloud)
> <wangli39@baidu.com>; Zhang,Yu(ACG Cloud) <zhangyu31@baidu.com>;
> stable <stable@vger.kernel.org>
> 主题: [PATCH] TTY: serial_core, add ->install
> 
> We need to compute the uart state only on the first open. This is usually what is
> done in the ->install hook. serial_core used to do this in ->open on every open.
> So move it to ->install.
> 
> As a side effect, it ensures the state is set properly in the window after
> tty_init_dev is called, but before uart_open. This fixes a bunch of races
> between tty_open and flush_to_ldisc we were dealing with recently.
> 
> One of such bugs was attempted to fix in commit fedb5760648a (serial:
> fix race between flush_to_ldisc and tty_open), but it only took care of a couple
> of functions (uart_start and uart_unthrottle).  I was able to reproduce the
> crash on a SLE system, but in uart_write_room which is also called from
> flush_to_ldisc via process_echoes. I was *unable* to reproduce the bug locally.
> It is due to having this patch in my queue since 2012!
> 
>  general protection fault: 0000 [#1] SMP KASAN PTI
>  CPU: 1 PID: 5 Comm: kworker/u4:0 Tainted: G             L
> 4.12.14-396-default #1 SLE15-SP1 (unreleased)
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.12.0-0-ga698c89-prebuilt.qemu.org 04/01/2014
>  Workqueue: events_unbound flush_to_ldisc
>  task: ffff8800427d8040 task.stack: ffff8800427f0000
>  RIP: 0010:uart_write_room+0xc4/0x590
>  RSP: 0018:ffff8800427f7088 EFLAGS: 00010202
>  RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
>  RDX: 000000000000002f RSI: 00000000000000ee RDI: ffff88003888bd90
>  RBP: ffffffffb9545850 R08: 0000000000000001 R09: 0000000000000400
>  R10: ffff8800427d825c R11: 000000000000006e R12: 1ffff100084fee12
>  R13: ffffc900004c5000 R14: ffff88003888bb28 R15: 0000000000000178
>  FS:  0000000000000000(0000) GS:ffff880043300000(0000)
> knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000561da0794148 CR3: 000000000ebf4000 CR4: 00000000000006e0
> Call Trace:
>   tty_write_room+0x6d/0xc0
>   __process_echoes+0x55/0x870
>   n_tty_receive_buf_common+0x105e/0x26d0
>   tty_ldisc_receive_buf+0xb7/0x1c0
>   tty_port_default_receive_buf+0x107/0x180
>   flush_to_ldisc+0x35d/0x5c0
> ...
> 
> 0 in rbx means tty->driver_data is NULL in uart_write_room. 0x178 is tried to
> be dereferenced (0x178 >> 3 is 0x2f in rdx) at uart_write_room+0xc4. 0x178 is
> exactly (struct uart_state *)NULL->refcount used in uart_port_lock from
> uart_write_room.
> 
> So revert the upstream commit here as my local patch should fix the whole
> family.
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Li RongQing <lirongqing@baidu.com>
> Cc: Wang Li <wangli39@baidu.com>
> Cc: Zhang Yu <zhangyu31@baidu.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: stable <stable@vger.kernel.org>
> ---
> 
> ============================= NOTE =============================
> 
> Could you test your use-case at Baidu, guys, please?
> 

Sorry, we have not the environment to test it, it happens when we upgrades BMC

-RongQing