diff options
| author | Dmitry Safonov | 2018-11-01 00:24:46 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman | 2018-12-05 12:16:33 +0100 |
| commit | 231f8fd0cca078bd4396dd7e380db813ac5736e2 (patch) | |
| tree | f4165fe647815ea4b48241ae34aa328b44f93f32 /drivers/tty/tty_ldsem.c | |
| parent | 77cab92a2cb15bcbdd7be0af773799e92d6a8546 (diff) | |
tty/ldsem: Wake up readers after timed out down_write()
ldsem_down_read() will sleep if there is pending writer in the queue.
If the writer times out, readers in the queue should be woken up,
otherwise they may miss a chance to acquire the semaphore until the last
active reader will do ldsem_up_read().
There was a couple of reports where there was one active reader and
other readers soft locked up:
Showing all locks held in the system:
2 locks held by khungtaskd/17:
#0: (rcu_read_lock){......}, at: watchdog+0x124/0x6d1
#1: (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3
2 locks held by askfirst/123:
#0: (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58
#1: (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4
Prevent readers wait for active readers to release ldisc semaphore.
Link: lkml.kernel.org/r/20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com
Link: lkml.kernel.org/r/20180907045041.GF1110@shao2-debian
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/tty_ldsem.c')
| -rw-r--r-- | drivers/tty/tty_ldsem.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c index 0c98d88f795a..b989ca26fc78 100644 --- a/drivers/tty/tty_ldsem.c +++ b/drivers/tty/tty_ldsem.c @@ -293,6 +293,16 @@ down_write_failed(struct ld_semaphore *sem, long count, long timeout) if (!locked) atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count); list_del(&waiter.list); + + /* + * In case of timeout, wake up every reader who gave the right of way + * to writer. Prevent separation readers into two groups: + * one that helds semaphore and another that sleeps. + * (in case of no contention with a writer) + */ + if (!locked && list_empty(&sem->write_wait)) + __ldsem_wake_readers(sem); + raw_spin_unlock_irq(&sem->wait_lock); __set_current_state(TASK_RUNNING); |