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  1. 24 7月, 2015 1 次提交
  3. 07 5月, 2015 1 次提交
  5. 07 11月, 2014 1 次提交
  7. 06 11月, 2014 8 次提交
  9. 08 1月, 2014 1 次提交
  11. 24 7月, 2013 8 次提交
  13. 19 3月, 2013 18 次提交
  15. 16 1月, 2013 2 次提交
    • S
      tty: don't deadlock while flushing workqueue · 852e4a81
      由 Sebastian Andrzej Siewior 提交于 
      Since commit 89c8d91e ("tty: localise the lock") I see a dead lock
in one of my dummy_hcd + g_nokia test cases. The first run was usually
okay, the second often resulted in a splat by lockdep and the third was
usually a dead lock.
Lockdep complained about tty->hangup_work and tty->legacy_mutex taken
both ways:
| ======================================================
| [ INFO: possible circular locking dependency detected ]
| 3.7.0-rc6+ #204 Not tainted
| -------------------------------------------------------
| kworker/2:1/35 is trying to acquire lock:
|  (&tty->legacy_mutex){+.+.+.}, at: [<c14051e6>] tty_lock_nested+0x36/0x80
|
| but task is already holding lock:
|  ((&tty->hangup_work)){+.+...}, at: [<c104f6e4>] process_one_work+0x124/0x5e0
|
| which lock already depends on the new lock.
|
| the existing dependency chain (in reverse order) is:
|
| -> #2 ((&tty->hangup_work)){+.+...}:
|        [<c107fe74>] lock_acquire+0x84/0x190
|        [<c104d82d>] flush_work+0x3d/0x240
|        [<c12e6986>] tty_ldisc_flush_works+0x16/0x30
|        [<c12e7861>] tty_ldisc_release+0x21/0x70
|        [<c12e0dfc>] tty_release+0x35c/0x470
|        [<c1105e28>] __fput+0xd8/0x270
|        [<c1105fcd>] ____fput+0xd/0x10
|        [<c1051dd9>] task_work_run+0xb9/0xf0
|        [<c1002a51>] do_notify_resume+0x51/0x80
|        [<c140550a>] work_notifysig+0x35/0x3b
|
| -> #1 (&tty->legacy_mutex/1){+.+...}:
|        [<c107fe74>] lock_acquire+0x84/0x190
|        [<c140276c>] mutex_lock_nested+0x6c/0x2f0
|        [<c14051e6>] tty_lock_nested+0x36/0x80
|        [<c1405279>] tty_lock_pair+0x29/0x70
|        [<c12e0bb8>] tty_release+0x118/0x470
|        [<c1105e28>] __fput+0xd8/0x270
|        [<c1105fcd>] ____fput+0xd/0x10
|        [<c1051dd9>] task_work_run+0xb9/0xf0
|        [<c1002a51>] do_notify_resume+0x51/0x80
|        [<c140550a>] work_notifysig+0x35/0x3b
|
| -> #0 (&tty->legacy_mutex){+.+.+.}:
|        [<c107f3c9>] __lock_acquire+0x1189/0x16a0
|        [<c107fe74>] lock_acquire+0x84/0x190
|        [<c140276c>] mutex_lock_nested+0x6c/0x2f0
|        [<c14051e6>] tty_lock_nested+0x36/0x80
|        [<c140523f>] tty_lock+0xf/0x20
|        [<c12df8e4>] __tty_hangup+0x54/0x410
|        [<c12dfcb2>] do_tty_hangup+0x12/0x20
|        [<c104f763>] process_one_work+0x1a3/0x5e0
|        [<c104fec9>] worker_thread+0x119/0x3a0
|        [<c1055084>] kthread+0x94/0xa0
|        [<c140ca37>] ret_from_kernel_thread+0x1b/0x28
|
|other info that might help us debug this:
|
|Chain exists of:
|  &tty->legacy_mutex --> &tty->legacy_mutex/1 --> (&tty->hangup_work)
|
| Possible unsafe locking scenario:
|
|       CPU0                    CPU1
|       ----                    ----
|  lock((&tty->hangup_work));
|                               lock(&tty->legacy_mutex/1);
|                               lock((&tty->hangup_work));
|  lock(&tty->legacy_mutex);
|
| *** DEADLOCK ***

Before the path mentioned tty_ldisc_release() look like this:

|	tty_ldisc_halt(tty);
|	tty_ldisc_flush_works(tty);
|	tty_lock();

As it can be seen, it first flushes the workqueue and then grabs the
tty_lock. Now we grab the lock first:

|	tty_lock_pair(tty, o_tty);
|	tty_ldisc_halt(tty);
|	tty_ldisc_flush_works(tty);

so lockdep's complaint seems valid.

The earlier version of this patch took the ldisc_mutex since the other
user of tty_ldisc_flush_works() (tty_set_ldisc()) did this.
Peter Hurley then said that it is should not be requried. Since it
wasn't done earlier, I dropped this part.
The code under tty_ldisc_kill() was executed earlier with the tty lock
taken so it is taken again.

I was able to reproduce the deadlock on v3.8-rc1, this patch fixes the
problem in my testcase. I didn't notice any problems so far.

Cc: Alan Cox <alan@linux.intel.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      852e4a81
    • I
      tty: Only wakeup the line discipline idle queue when queue is active · bd5d7ce9
      由 Ivo Sieben 提交于 
      Before waking up the tty line discipline idle queue first check if the queue is
active (non empty). This prevents unnecessary entering the critical section in
the wake_up() function and therefore avoid needless scheduling overhead on a
PREEMPT_RT system caused by two processes being in the same critical section.
Signed-off-by: NIvo Sieben <meltedpianoman@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      bd5d7ce9