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Peter Zijlstra 870d910e1a serial: pl011: Fix lockdep splat when handling magic-sysrq interrupt 
commit 534cf755d9 upstream.

Issuing a magic-sysrq via the PL011 causes the following lockdep splat,
which is easily reproducible under QEMU:

  | sysrq: Changing Loglevel
  | sysrq: Loglevel set to 9
  |
  | ======================================================
  | WARNING: possible circular locking dependency detected
  | 5.9.0-rc7 #1 Not tainted
  | ------------------------------------------------------
  | systemd-journal/138 is trying to acquire lock:
  | ffffab133ad950c0 (console_owner){-.-.}-{0:0}, at: console_lock_spinning_enable+0x34/0x70
  |
  | but task is already holding lock:
  | ffff0001fd47b098 (&port_lock_key){-.-.}-{2:2}, at: pl011_int+0x40/0x488
  |
  | which lock already depends on the new lock.

  [...]

  |  Possible unsafe locking scenario:
  |
  |        CPU0                    CPU1
  |        ----                    ----
  |   lock(&port_lock_key);
  |                                lock(console_owner);
  |                                lock(&port_lock_key);
  |   lock(console_owner);
  |
  |  *** DEADLOCK ***

The issue being that CPU0 takes 'port_lock' on the irq path in pl011_int()
before taking 'console_owner' on the printk() path, whereas CPU1 takes
the two locks in the opposite order on the printk() path due to setting
the "console_owner" prior to calling into into the actual console driver.

Fix this in the same way as the msm-serial driver by dropping 'port_lock'
before handling the sysrq.

Cc: <stable@vger.kernel.org> # 4.19+
Cc: Russell King <linux@armlinux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20200811101313.GA6970@willie-the-truck
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Tested-by: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200930120432.16551-1-will@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2020-11-01 12:01:06 +01:00
..
hvc tty: hvcs: Don't NULL tty->driver_data until hvcs_cleanup() 2020-10-29 09:57:38 +01:00
ipwireless tty: ipwireless: fix error handling 2020-10-29 09:58:08 +01:00
serdev serdev: ttyport: restore client ops on deregistration 2020-02-28 17:22:19 +01:00
serial serial: pl011: Fix lockdep splat when handling magic-sysrq interrupt 2020-11-01 12:01:06 +01:00
vt vt_ioctl: change VT_RESIZEX ioctl to check for error return from vc_resize() 2020-09-03 11:27:03 +02:00
Kconfig
…
Makefile
…
amiserial.c
…
cyclades.c
…
ehv_bytechan.c tty: evh_bytechan: Fix out of bounds accesses 2020-04-23 10:36:44 +02:00
goldfish.c
…
isicom.c
…
mips_ejtag_fdc.c
…
moxa.c
…
moxa.h
…
mxser.c
…
mxser.h
…
n_gsm.c tty: n_gsm: Fix bogus i++ in gsm_data_kick 2020-06-24 17:50:29 +02:00
n_hdlc.c tty: n_hdlc: fix build on SPARC 2019-10-04 15:14:20 +02:00
n_null.c
…
n_r3964.c
…
n_tracerouter.c
…
n_tracesink.c
…
n_tracesink.h
…
n_tty.c
…
nozomi.c
…
pty.c pty: do tty_flip_buffer_push without port->lock in pty_write 2020-10-29 09:57:38 +01:00
rocket.c tty: rocket, avoid OOB access 2020-04-29 16:33:17 +02:00
rocket.h
…
rocket_int.h
…
synclink.c
…
synclink_gt.c tty: synclink_gt: Adjust indentation in several functions 2020-02-24 08:36:47 +01:00
synclinkmp.c tty: synclinkmp: Adjust indentation in several functions 2020-02-24 08:36:47 +01:00
sysrq.c
…
tty_audit.c
…
tty_baudrate.c
…
tty_buffer.c
…
tty_io.c tty: fix compat TIOCGSERIAL checking wrong function ptr 2020-03-25 08:25:52 +01:00
tty_ioctl.c
…
tty_jobctrl.c
…
tty_ldisc.c
…
tty_ldsem.c
…
tty_mutex.c
…
tty_port.c serdev: ttyport: restore client ops on deregistration 2020-02-28 17:22:19 +01:00
ttynull.c
…
vcc.c sparc64: vcc: Fix error return code in vcc_probe() 2020-10-01 13:17:57 +02:00