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aefceaf453
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Peter Hurley aefceaf453 n_tty: Fix termios_rwsem lockdep false positive 
Lockdep reports a circular lock dependency between
atomic_read_lock and termios_rwsem [1]. However, a lock
order deadlock is not possible since CPU1 only holds a
read lock which cannot prevent CPU0 from also acquiring
a read lock on the same r/w semaphore.

Unfortunately, lockdep cannot currently distinguish whether
the locks are read or write for any particular lock graph,
merely that the locks _were_ previously read and/or write.

Until lockdep is fixed, re-order atomic_read_lock so
termios_rwsem can be dropped and reacquired without
triggering lockdep.

Patch based on original posted here https://lkml.org/lkml/2013/8/1/510
by Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

[1] Initial lockdep report from Artem Savkov <artem.savkov@gmail.com>

 ======================================================
 [ INFO: possible circular locking dependency detected ]
 3.11.0-rc3-next-20130730+ #140 Tainted: G        W
 -------------------------------------------------------
 bash/1198 is trying to acquire lock:
  (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660

 but task is already holding lock:
  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660

 which lock already depends on the new lock.

 the existing dependency chain (in reverse order) is:

 -> #1 (&ldata->atomic_read_lock){+.+...}:
        [<ffffffff811111cc>] validate_chain+0x73c/0x850
        [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
        [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
        [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
        [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
        [<ffffffff816a3bb6>] tty_read+0x86/0xf0
        [<ffffffff811f21d3>] vfs_read+0xc3/0x130
        [<ffffffff811f2702>] SyS_read+0x62/0xa0
        [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b

 -> #0 (&tty->termios_rwsem){++++..}:
        [<ffffffff8111064f>] check_prev_add+0x14f/0x590
        [<ffffffff811111cc>] validate_chain+0x73c/0x850
        [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
        [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
        [<ffffffff81d372c1>] down_read+0x51/0xa0
        [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
        [<ffffffff816a3bb6>] tty_read+0x86/0xf0
        [<ffffffff811f21d3>] vfs_read+0xc3/0x130
        [<ffffffff811f2702>] SyS_read+0x62/0xa0
        [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b

 other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(&ldata->atomic_read_lock);
                                lock(&tty->termios_rwsem);
                                lock(&ldata->atomic_read_lock);
   lock(&tty->termios_rwsem);

  *** DEADLOCK ***

 2 locks held by bash/1198:
  #0:  (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
  #1:  (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660

 stack backtrace:
 CPU: 1 PID: 1198 Comm: bash Tainted: G        W    3.11.0-rc3-next-20130730+ #140
 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
  0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
  0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
  ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
 Call Trace:
  [<ffffffff81d34074>] dump_stack+0x59/0x7d
  [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
  [<ffffffff8111064f>] check_prev_add+0x14f/0x590
  [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
  [<ffffffff811111cc>] validate_chain+0x73c/0x850
  [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
  [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
  [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
  [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
  [<ffffffff81d372c1>] down_read+0x51/0xa0
  [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
  [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
  [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
  [<ffffffff816a3bb6>] tty_read+0x86/0xf0
  [<ffffffff811f21d3>] vfs_read+0xc3/0x130
  [<ffffffff811f2702>] SyS_read+0x62/0xa0
  [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
  [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b

Reported-by: Artem Savkov <artem.savkov@gmail.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-08-12 11:10:17 -07:00
..
hvc tty/hvc_iucv: Disconnect IUCV connection when lowering DTR 2013-07-24 15:21:13 -07:00
ipwireless tty: ipwireless: Remove redundant NULL check before kfree 2013-03-15 13:58:32 -07:00
serial serial: pxa: Staticize local symbols 2013-08-12 11:10:16 -07:00
vt vt: make the default color configurable 2013-08-05 15:06:46 +08:00
amiserial.c TTY: amiserial, use module_platform_driver_probe() 2013-03-15 13:55:23 -07:00
bfin_jtag_comm.c TTY: switch tty_flip_buffer_push 2013-01-15 22:30:15 -08:00
cyclades.c TTY: add tty_port_tty_hangup helper 2013-03-18 16:24:29 -07:00
ehv_bytechan.c TTY: ehv_bytechan: add missing platform_driver_unregister() when module exit 2013-05-20 12:15:59 -07:00
goldfish.c goldfish: move to tty_port for flip buffers 2013-01-25 08:09:38 -08:00
isicom.c TTY: switch tty_flip_buffer_push 2013-01-15 22:30:15 -08:00
Kconfig tty: metag_da: Add metag DA TTY driver 2013-02-06 11:10:17 -08:00
Makefile tty: Add timed, writer-prioritized rw semaphore 2013-05-20 12:30:32 -07:00
metag_da.c tty: metag_da: avoid getting tty kref in dashtty_timer() 2013-02-06 11:10:17 -08:00
moxa.c TTY: add tty_port_tty_hangup helper 2013-03-18 16:24:29 -07:00
moxa.h
mxser.c tty: mxser: Fix build warning introduced by dfc7b837c7 (Re: linux-next: build warning after merge of the tty.current tree) 2013-05-22 10:26:02 -07:00
mxser.h
n_gsm.c Drivers: tty: n_gsm.c: fixed 7 errors & 6 warnings that checkpatch complained 2013-07-24 15:21:13 -07:00
n_hdlc.c
n_r3964.c
n_tracerouter.c
n_tracesink.c
n_tracesink.h
n_tty.c n_tty: Fix termios_rwsem lockdep false positive 2013-08-12 11:10:17 -07:00
nozomi.c TTY: add tty_port_tty_hangup helper 2013-03-18 16:24:29 -07:00
pty.c tty: Fix lock order in tty_do_resize() 2013-07-24 15:12:53 -07:00
rocket_int.h
rocket.c TTY: rocket, fix more no-PCI warnings 2013-05-20 12:15:59 -07:00
rocket.h
synclink_gt.c TTY: synclink_gt: fix DTR being raised on hang up 2013-04-12 14:08:17 -07:00
synclink.c TTY: synclink: replace bitmasks add operation with OR operation. 2013-07-29 12:47:37 -07:00
synclinkmp.c TTY: snyclinkmp: calculating wrong addresses 2013-07-24 15:23:38 -07:00
sysrq.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2013-07-04 15:35:08 -07:00
tty_audit.c audit: do not needlessly take a lock in tty_audit_exit 2013-04-30 15:31:28 -04:00
tty_buffer.c tty: Remove private constant from global namespace 2013-07-23 16:47:10 -07:00
tty_io.c tty: Only hangup once 2013-08-02 11:47:42 +08:00
tty_ioctl.c tty: Only guarantee termios read safety for throttle/unthrottle 2013-07-23 16:43:02 -07:00
tty_ldisc.c tty: Convert termios_mutex to termios_rwsem 2013-07-23 16:43:01 -07:00
tty_ldsem.c tty: Add timed, writer-prioritized rw semaphore 2013-05-20 12:30:32 -07:00
tty_mutex.c tty: tty_mutex.c: Fixed coding style warning (using printk) 2012-10-24 11:34:51 -07:00
tty_port.c tty_port: Fix refcounting leak in tty_port_tty_hangup() 2013-07-26 16:34:00 -07:00