diff options
author | Mikulas Patocka <mpatocka@redhat.com> | 2015-11-19 07:36:50 -0500 |
---|---|---|
committer | Mike Snitzer <snitzer@redhat.com> | 2015-11-19 13:38:30 -0500 |
commit | bcbd94ff481ec1d7b5c824d90df82d0faafabd35 (patch) | |
tree | ac755d832487bd9cce6ee61ac319be6ed09574e9 /drivers/md/dm-thin.c | |
parent | 43e43c9ea60a7a1831ec823773e924d2dadefd44 (diff) | |
download | linux-stable-bcbd94ff481ec1d7b5c824d90df82d0faafabd35.tar.gz linux-stable-bcbd94ff481ec1d7b5c824d90df82d0faafabd35.tar.bz2 linux-stable-bcbd94ff481ec1d7b5c824d90df82d0faafabd35.zip |
dm crypt: fix a possible hang due to race condition on exit
A kernel thread executes __set_current_state(TASK_INTERRUPTIBLE),
__add_wait_queue, spin_unlock_irq and then tests kthread_should_stop().
It is possible that the processor reorders memory accesses so that
kthread_should_stop() is executed before __set_current_state(). If such
reordering happens, there is a possible race on thread termination:
CPU 0:
calls kthread_should_stop()
it tests KTHREAD_SHOULD_STOP bit, returns false
CPU 1:
calls kthread_stop(cc->write_thread)
sets the KTHREAD_SHOULD_STOP bit
calls wake_up_process on the kernel thread, that sets the thread
state to TASK_RUNNING
CPU 0:
sets __set_current_state(TASK_INTERRUPTIBLE)
spin_unlock_irq(&cc->write_thread_wait.lock)
schedule() - and the process is stuck and never terminates, because the
state is TASK_INTERRUPTIBLE and wake_up_process on CPU 1 already
terminated
Fix this race condition by using a new flag DM_CRYPT_EXIT_THREAD to
signal that the kernel thread should exit. The flag is set and tested
while holding cc->write_thread_wait.lock, so there is no possibility of
racy access to the flag.
Also, remove the unnecessary set_task_state(current, TASK_RUNNING)
following the schedule() call. When the process was woken up, its state
was already set to TASK_RUNNING. Other kernel code also doesn't set the
state to TASK_RUNNING following schedule() (for example,
do_wait_for_common in completion.c doesn't do it).
Fixes: dc2676210c42 ("dm crypt: offload writes to thread")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md/dm-thin.c')
0 files changed, 0 insertions, 0 deletions