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received-spf: None (protection.outlook.com: nxp.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: s40+nKV4xcUZHA9BEqDBzeArWPVauYC4svXdsJaQolDtRC57mBm2XuRBaptckzP14WYcnYKFApjIVn3Ovjid9NF1/2dAl6hO31atrbwTTbymrnVCOcti9+XLcOaQjsSQH0qKsvtQBKSNHsb7YHiYXydZWawIzz9ocw3zxtyIm640A0SUjpI8hDlqsplXJRmbXkLn4LYR4gX9KQWMqvhwXBK01gWIUU+cnxC6e7JPwKkzK2e7sq/Gk993ro/LBWkqfdujj/bKF1Syrb9vMf5VV6voAJtGQt8zvEdqIDtsJ1KYSkMlwSbb6DN4b8+oAWviMRE+IJxyinScCnEm+tu+lg5pFQOSAS7LJZGAUxpcuaWD7QsDnUGy35ccJqo+GnJ86h2fjyGqCdJ0MCN4Hpd9KprgC3Mr9p+MX5VtVIsP60nx5/YwZNZNucFDN32cb7Mc Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-Network-Message-Id: 966098bc-9103-4e92-fcef-08d76f32dc6b X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Nov 2019 10:00:53.7604 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: /LBfY1nMPGrdb/4YuG6PjVmsX5p5AK3L4Nltqwhc+FoKW4kPBEFA0h7TauH5X1BUPFCvS6T4bf6PZwB623omdQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR0402MB3423 Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org From: Fugang Duan commit dbdda842fe96 ("printk: Add console owner and waiter logic to load balance console writes") introduces the lockdep issue for imx serial driver in sysrq case: CPU0 CPU1 ---- ---- lock(&port_lock_key); lock(console_owner); lock(&port_lock_key); lock(console_owner); It should unlock port_lock_key in handle_sysrq(). lockdep splats: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D WARNING: possible circular locking dependency detected ------------------------------------------------------ swapper/0/0 is trying to acquire lock: c141e540 (console_owner){-...}, at: console_unlock+0x180/0x5e4 but task is already holding lock: d864e450 (&port_lock_key){-.-.}, at: imx_uart_rxint+0x18/0x294 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&port_lock_key){-.-.}: imx_uart_console_write+0x1b4/0x1dc console_unlock+0x2a4/0x5e4 register_console+0x1ec/0x3b4 uart_add_one_port+0x480/0x4e8 platform_drv_probe+0x48/0x98 really_probe+0x1d8/0x34c driver_probe_device+0x5c/0x168 device_driver_attach+0x58/0x60 __driver_attach+0x58/0xd0 bus_for_each_dev+0x74/0xbc bus_add_driver+0x150/0x1dc driver_register+0x74/0x108 imx_uart_init+0x20/0x40 do_one_initcall+0x84/0x348 kernel_init_freeable+0x11c/0x1e0 kernel_init+0x8/0x110 ret_from_fork+0x14/0x20 0x0 -> #0 (console_owner){-...}: lock_acquire+0xcc/0x204 console_unlock+0x208/0x5e4 vprintk_emit+0x108/0x2c8 vprintk_default+0x20/0x28 printk+0x2c/0x58 __handle_sysrq+0x178/0x1f0 imx_uart_rxint+0x234/0x294 imx_uart_int+0x210/0x2f0 __handle_irq_event_percpu+0x48/0x34c handle_irq_event_percpu+0x2c/0x88 handle_irq_event+0x38/0x5c handle_fasteoi_irq+0xc8/0x180 generic_handle_irq+0x20/0x34 __handle_domain_irq+0x64/0xdc gic_handle_irq+0x48/0x9c __irq_svc+0x70/0x98 cpuidle_enter_state+0x16c/0x520 cpuidle_enter_state+0x16c/0x520 cpuidle_enter+0x28/0x38 do_idle+0x1dc/0x2b0 cpu_startup_entry+0x18/0x1c start_kernel+0x404/0x4cc other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&port_lock_key); lock(console_owner); lock(&port_lock_key); lock(console_owner); *** DEADLOCK *** 3 locks held by swapper/0/0: #0: d864e450 (&port_lock_key){-.-.}, at: imx_uart_rxint+0x18/0x294 #1: c141eb88 (rcu_read_lock){....}, at: __handle_sysrq+0x0/0x1f0 #2: c141e4c0 (console_lock){+.+.}, at: vprintk_emit+0xfc/0x2c8 stack backtrace: CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) [] (unwind_backtrace) from [] (show_stack+0x10/0x14) [] (show_stack) from [] (dump_stack+0xe0/0x114) [] (dump_stack) from [] (check_noncircular+0x138/0x1ec) [] (check_noncircular) from [] (__lock_acquire+0xe00/0x= 2418) [] (__lock_acquire) from [] (lock_acquire+0xcc/0x204) [] (lock_acquire) from [] (console_unlock+0x208/0x5e4) [] (console_unlock) from [] (vprintk_emit+0x108/0x2c8) [] (vprintk_emit) from [] (vprintk_default+0x20/0x28) [] (vprintk_default) from [] (printk+0x2c/0x58) [] (printk) from [] (__handle_sysrq+0x178/0x1f0) [] (__handle_sysrq) from [] (imx_uart_rxint+0x234/0x294= ) [] (imx_uart_rxint) from [] (imx_uart_int+0x210/0x2f0) [] (imx_uart_int) from [] (__handle_irq_event_percpu+0x= 48/0x34c) [] (__handle_irq_event_percpu) from [] (handle_irq_even= t_percpu+0x2c/0x88) [] (handle_irq_event_percpu) from [] (handle_irq_event+= 0x38/0x5c) [] (handle_irq_event) from [] (handle_fasteoi_irq+0xc8/= 0x180) [] (handle_fasteoi_irq) from [] (generic_handle_irq+0x2= 0/0x34) [] (generic_handle_irq) from [] (__handle_domain_irq+0x= 64/0xdc) [] (__handle_domain_irq) from [] (gic_handle_irq+0x48/0= x9c) [] (gic_handle_irq) from [] (__irq_svc+0x70/0x98) Exception stack(0xc1401ed8 to 0xc1401f20) 1ec0: 00000001 000000= 06 1ee0: 00000000 c140c600 00000001 5b0881e8 c140f934 db6eadb8 c1504668 000009= 8b 1f00: 0000098b 5c28eb3d 00000000 c1401f28 c0194520 c0938fcc 20070013 ffffff= ff [] (__irq_svc) from [] (cpuidle_enter_state+0x16c/0x520= ) [] (cpuidle_enter_state) from [] (cpuidle_enter+0x28/0x= 38) [] (cpuidle_enter) from [] (do_idle+0x1dc/0x2b0) [] (do_idle) from [] (cpu_startup_entry+0x18/0x1c) [] (cpu_startup_entry) from [] (start_kernel+0x404/0x4c= c) Signed-off-by: Fugang Duan --- drivers/tty/serial/imx.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index a9e20e6..a665439 100644 --- a/drivers/tty/serial/imx.c +++ b/drivers/tty/serial/imx.c @@ -736,6 +736,7 @@ static irqreturn_t imx_uart_rxint(int irq, void *dev_id= ) =20 while (imx_uart_readl(sport, USR2) & USR2_RDR) { u32 usr2; + int sysrq; =20 flg =3D TTY_NORMAL; sport->port.icount.rx++; @@ -749,7 +750,11 @@ static irqreturn_t imx_uart_rxint(int irq, void *dev_i= d) continue; } =20 - if (uart_handle_sysrq_char(&sport->port, (unsigned char)rx)) + spin_unlock(&sport->port.lock); + sysrq =3D uart_handle_sysrq_char(&sport->port, (unsigned char)rx); + spin_lock(&sport->port.lock); + + if (sysrq) continue; =20 if (unlikely(rx & URXD_ERR)) { --=20 2.7.4