From bf7f5ee36ec356c50821e865f8a1d3871a2d9810 Mon Sep 17 00:00:00 2001 From: Viresh Kumar Date: Mon, 19 Aug 2013 20:14:19 +0530 Subject: [PATCH] tty: serial: mpsc: drop uart_port->lock before calling tty_flip_buffer_push() The current driver triggers a lockdep warning for if tty_flip_buffer_push() is called with uart_port->lock locked. This never shows up on UP kernels and comes up only on SMP kernels. Crash looks like this (produced with samsung.c driver): ----- [] (unwind_backtrace+0x0/0xf8) from [] (show_stack+0x10/0x14) [] (show_stack+0x10/0x14) from [] (dump_stack+0x6c/0xac) [] (dump_stack+0x6c/0xac) from [] (do_raw_spin_unlock+0xc4/0xd8) [] (do_raw_spin_unlock+0xc4/0xd8) from [] (_raw_spin_unlock_irqrestore+0xc/0) [] (_raw_spin_unlock_irqrestore+0xc/0x38) from [] (s3c24xx_serial_rx_chars+0) [] (s3c24xx_serial_rx_chars+0x12c/0x260) from [] (s3c64xx_serial_handle_irq+) [] (s3c64xx_serial_handle_irq+0x48/0x60) from [] (handle_irq_event_percpu+0x) [] (handle_irq_event_percpu+0x50/0x194) from [] (handle_irq_event+0x3c/0x5c) [] (handle_irq_event+0x3c/0x5c) from [] (handle_fasteoi_irq+0x80/0x13c) [] (handle_fasteoi_irq+0x80/0x13c) from [] (generic_handle_irq+0x20/0x30) [] (generic_handle_irq+0x20/0x30) from [] (handle_IRQ+0x38/0x94) [] (handle_IRQ+0x38/0x94) from [] (gic_handle_irq+0x34/0x68) [] (gic_handle_irq+0x34/0x68) from [] (__irq_svc+0x40/0x70) Exception stack(0xc04cdf70 to 0xc04cdfb8) df60: 00000000 00000000 0000166e 00000000 df80: c04cc000 c050278f c050278f 00000001 c04d444c 410fc0f4 c03649b0 00000000 dfa0: 00000001 c04cdfb8 c000f758 c000f75c 60070013 ffffffff [] (__irq_svc+0x40/0x70) from [] (arch_cpu_idle+0x28/0x30) [] (arch_cpu_idle+0x28/0x30) from [] (cpu_startup_entry+0x5c/0x148) [] (cpu_startup_entry+0x5c/0x148) from [] (start_kernel+0x334/0x38c) BUG: spinlock lockup suspected on CPU#0, kworker/0:1/360 lock: s3c24xx_serial_ports+0x1d8/0x370, .magic: dead4ead, .owner: /-1, .owner_cpu: -1 CPU: 0 PID: 360 Comm: kworker/0:1 Not tainted 3.11.0-rc6-next-20130819-00003-g75485f1 #2 Workqueue: events flush_to_ldisc [] (unwind_backtrace+0x0/0xf8) from [] (show_stack+0x10/0x14) [] (show_stack+0x10/0x14) from [] (dump_stack+0x6c/0xac) [] (dump_stack+0x6c/0xac) from [] (do_raw_spin_lock+0x100/0x17c) [] (do_raw_spin_lock+0x100/0x17c) from [] (_raw_spin_lock_irqsave+0x20/0x28) [] (_raw_spin_lock_irqsave+0x20/0x28) from [] (uart_start+0x18/0x34) [] (uart_start+0x18/0x34) from [] (__receive_buf+0x4b4/0x738) [] (__receive_buf+0x4b4/0x738) from [] (n_tty_receive_buf2+0x30/0x98) [] (n_tty_receive_buf2+0x30/0x98) from [] (flush_to_ldisc+0xec/0x138) [] (flush_to_ldisc+0xec/0x138) from [] (process_one_work+0xfc/0x348) [] (process_one_work+0xfc/0x348) from [] (worker_thread+0x138/0x37c) [] (worker_thread+0x138/0x37c) from [] (kthread+0xa4/0xb0) [] (kthread+0xa4/0xb0) from [] (ret_from_fork+0x14/0x3c) ----- Release the port lock before calling tty_flip_buffer_push() and reacquire it after the call. Similar stuff was already done for few other drivers in the past, like: commit 2389b272168ceec056ca1d8a870a97fa9c26e11a Author: Thomas Gleixner Date: Tue May 29 21:53:50 2007 +0100 [ARM] 4417/1: Serial: Fix AMBA drivers locking Signed-off-by: Viresh Kumar Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/mpsc.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/tty/serial/mpsc.c b/drivers/tty/serial/mpsc.c index fba52578d02f..8d702677acc5 100644 --- a/drivers/tty/serial/mpsc.c +++ b/drivers/tty/serial/mpsc.c @@ -934,7 +934,7 @@ static int serial_polled; ****************************************************************************** */ -static int mpsc_rx_intr(struct mpsc_port_info *pi) +static int mpsc_rx_intr(struct mpsc_port_info *pi, unsigned long *flags) { struct mpsc_rx_desc *rxre; struct tty_port *port = &pi->port.state->port; @@ -969,8 +969,11 @@ static int mpsc_rx_intr(struct mpsc_port_info *pi) #endif /* Following use of tty struct directly is deprecated */ if (tty_buffer_request_room(port, bytes_in) < bytes_in) { - if (port->low_latency) + if (port->low_latency) { + spin_unlock_irqrestore(&pi->port.lock, *flags); tty_flip_buffer_push(port); + spin_lock_irqsave(&pi->port.lock, *flags); + } /* * If this failed then we will throw away the bytes * but must do so to clear interrupts. @@ -1080,7 +1083,9 @@ next_frame: if ((readl(pi->sdma_base + SDMA_SDCM) & SDMA_SDCM_ERD) == 0) mpsc_start_rx(pi); + spin_unlock_irqrestore(&pi->port.lock, *flags); tty_flip_buffer_push(port); + spin_lock_irqsave(&pi->port.lock, *flags); return rc; } @@ -1222,7 +1227,7 @@ static irqreturn_t mpsc_sdma_intr(int irq, void *dev_id) spin_lock_irqsave(&pi->port.lock, iflags); mpsc_sdma_intr_ack(pi); - if (mpsc_rx_intr(pi)) + if (mpsc_rx_intr(pi, &iflags)) rc = IRQ_HANDLED; if (mpsc_tx_intr(pi)) rc = IRQ_HANDLED;