3.16.74-rc1 review patch. If anyone has any objections, please let me know.
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From: Jiri Slaby jslaby@suse.cz
commit 4cdd17ba1dff20ffc99fdbd2e6f0201fc7fe67df upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [bwh: Backported to 3.16: The previous fix didn't apply, so we don't need to revert it here.] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1541,6 +1541,16 @@ static void uart_dtr_rts(struct tty_port uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS); }
+static int uart_install(struct tty_driver *driver, struct tty_struct *tty) +{ + struct uart_driver *drv = driver->driver_state; + struct uart_state *state = drv->state + tty->index; + + tty->driver_data = state; + + return tty_standard_install(driver, tty); +} + /* * Calls to uart_open are serialised by the tty_lock in * drivers/tty/tty_io.c:tty_open() @@ -1553,9 +1563,8 @@ static void uart_dtr_rts(struct tty_port */ static int uart_open(struct tty_struct *tty, struct file *filp) { - struct uart_driver *drv = (struct uart_driver *)tty->driver->driver_state; int retval, line = tty->index; - struct uart_state *state = drv->state + line; + struct uart_state *state = tty->driver_data; struct tty_port *port = &state->port;
pr_debug("uart_open(%d) called\n", line); @@ -1583,7 +1592,6 @@ static int uart_open(struct tty_struct * * uart_close() will decrement the driver module use count. * Any failures from here onwards should not touch the count. */ - tty->driver_data = state; state->uart_port->state = state; state->port.low_latency = (state->uart_port->flags & UPF_LOW_LATENCY) ? 1 : 0; @@ -2265,6 +2273,7 @@ static void uart_poll_put_char(struct tt #endif
static const struct tty_operations uart_ops = { + .install = uart_install, .open = uart_open, .close = uart_close, .write = uart_write,