slip: Fix deadlock in write_wakeup

2014-06-17T04:29:12Z

Use schedule_work() to avoid potentially taking the spinlock in interrupt context. Commit cc9fa74e2a ("slip/slcan: added locking in wakeup function") added necessary locking to the wakeup function and 367525c8c2/ddcde142be ("can: slcan: Fix spinlock variant") converted it to spin_lock_bh() because the lock is also taken in timers. Disabling softirqs is not sufficient, however, as tty drivers may call write_wakeup from interrupt context. This driver calls tty->ops->write() with its spinlock held, which may immediately cause an interrupt on the same CPU and subsequent spin_bug(). Simply converting to spin_lock_irq/irqsave() prevents this deadlock, but causes lockdep to point out a possible circular locking dependency between these locks: (&(&sl->lock)->rlock){-.....}, at: slip_write_wakeup (&port_lock_key){-.....}, at: serial8250_handle_irq.part.13 The slip transmit is holding the slip spinlock when calling the tty write. This grabs the port lock. On an interrupt, the handler grabs the port lock and calls write_wakeup which grabs the slip lock. This could be a problem if a serial interrupt occurs on another CPU during the slip transmit. To deal with these issues, don't grab the lock in the wakeup function by deferring the writeout to a workqueue. Also hold the lock during close when de-assigning the tty pointer to safely disarm the worker and timers. This bug is easily reproducible on the first transmit when slip is used with the standard 8250 serial driver. [] (spin_bug+0x0/0x38) from [] (do_raw_spin_lock+0x60/0x1d0) r5:eab27000 r4:ec02754c [] (do_raw_spin_lock+0x0/0x1d0) from [] (_raw_spin_lock+0x28/0x2c) r10:0000001f r9:eabb814c r8:eabb8140 r7:40070193 r6:ec02754c r5:eab27000 r4:ec02754c r3:00000000 [] (_raw_spin_lock+0x0/0x2c) from [] (slip_write_wakeup+0x50/0xe0 [slip]) r4:ec027540 r3:00000003 [] (slip_write_wakeup+0x0/0xe0 [slip]) from [] (tty_wakeup+0x48/0x68) r6:00000000 r5:ea80c480 r4:eab27000 r3:bf3a01d0 [] (tty_wakeup+0x0/0x68) from [] (uart_write_wakeup+0x2c/0x30) r5:ed68ea90 r4:c06790d8 [] (uart_write_wakeup+0x0/0x30) from [] (serial8250_tx_chars+0x114/0x170) [] (serial8250_tx_chars+0x0/0x170) from [] (serial8250_handle_irq+0xa0/0xbc) r6:000000c2 r5:00000060 r4:c06790d8 r3:00000000 [] (serial8250_handle_irq+0x0/0xbc) from [] (dw8250_handle_irq+0x38/0x64) r7:00000000 r6:edd2f390 r5:000000c2 r4:c06790d8 [] (dw8250_handle_irq+0x0/0x64) from [] (serial8250_interrupt+0x44/0xc4) r6:00000000 r5:00000000 r4:c06791c4 r3:c029336c [] (serial8250_interrupt+0x0/0xc4) from [] (handle_irq_event_percpu+0xb4/0x2b0) r10:c06790d8 r9:eab27000 r8:00000000 r7:00000000 r6:0000001f r5:edd52980 r4:ec53b6c0 r3:c028d2b0 [] (handle_irq_event_percpu+0x0/0x2b0) from [] (handle_irq_event+0x4c/0x6c) r10:c06790d8 r9:eab27000 r8:c0673ae0 r7:c05c2020 r6:ec53b6c0 r5:edd529d4 r4:edd52980 [] (handle_irq_event+0x0/0x6c) from [] (handle_level_irq+0xe8/0x100) r6:00000000 r5:edd529d4 r4:edd52980 r3:00022000 [] (handle_level_irq+0x0/0x100) from [] (generic_handle_irq+0x30/0x40) r5:0000001f r4:0000001f [] (generic_handle_irq+0x0/0x40) from [] (handle_IRQ+0xd0/0x13c) r4:ea997b18 r3:000000e0 [] (handle_IRQ+0x0/0x13c) from [] (armada_370_xp_handle_irq+0x4c/0x118) r8:000003ff r7:ea997b18 r6:ffffffff r5:60070013 r4:c0674dc0 [] (armada_370_xp_handle_irq+0x0/0x118) from [] (__irq_svc+0x40/0x70) Exception stack(0xea997b18 to 0xea997b60) 7b00: 00000001 20070013 7b20: 00000000 0000000b 20070013 eab27000 20070013 00000000 ed10103e eab27000 7b40: c06790d8 ea997b74 ea997b60 ea997b60 c04186c0 c04186c8 60070013 ffffffff r9:eab27000 r8:ed10103e r7:ea997b4c r6:ffffffff r5:60070013 r4:c04186c8 [] (_raw_spin_unlock_irqrestore+0x0/0x54) from [] (uart_start+0x40/0x44) r4:c06790d8 r3:c028ddd8 [] (uart_start+0x0/0x44) from [] (uart_write+0xe4/0xf4) r6:0000003e r5:00000000 r4:ed68ea90 r3:0000003e [] (uart_write+0x0/0xf4) from [] (sl_xmit+0x1c4/0x228 [slip]) r10:ed388e60 r9:0000003c r8:ffffffdd r7:0000003e r6:ec02754c r5:ea717eb8 r4:ec027000 [] (sl_xmit+0x0/0x228 [slip]) from [] (dev_hard_start_xmit+0x39c/0x6d0) r8:eaf163c0 r7:ec027000 r6:ea717eb8 r5:00000000 r4:00000000 Signed-off-by: Tyler Hall Cc: Oliver Hartkopp Cc: Andre Naujoks Cc: David S. Miller Cc: linux-kernel@vger.kernel.org Signed-off-by: David S. Miller

slip: Move the SLIP drivers

2011-08-27T07:58:36Z

Move the Serial Line Internet Protocol (SLIP) drivers into drivers/net/slip/ and make the necessary Kconfig and Makefile changes. Signed-off-by: Jeff Kirsher Acked-by: Alan Cox

kernel/drivers/net/slip/slip.h, branch linux-4.3.y

slip: Fix deadlock in write_wakeup

slip: Move the SLIP drivers