-----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
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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