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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 | |
parent | 43e43c9ea60a7a1831ec823773e924d2dadefd44 (diff) | |
download | linux-bcbd94ff481ec1d7b5c824d90df82d0faafabd35.tar.bz2 |
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')
-rw-r--r-- | drivers/md/dm-crypt.c | 22 |
1 files changed, 13 insertions, 9 deletions
diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index 917d47e290ae..3147c8d09ea8 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -112,7 +112,8 @@ struct iv_tcw_private { * and encrypts / decrypts at the same time. */ enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID, - DM_CRYPT_SAME_CPU, DM_CRYPT_NO_OFFLOAD }; + DM_CRYPT_SAME_CPU, DM_CRYPT_NO_OFFLOAD, + DM_CRYPT_EXIT_THREAD}; /* * The fields in here must be read only after initialization. @@ -1203,20 +1204,18 @@ continue_locked: if (!RB_EMPTY_ROOT(&cc->write_tree)) goto pop_from_list; + if (unlikely(test_bit(DM_CRYPT_EXIT_THREAD, &cc->flags))) { + spin_unlock_irq(&cc->write_thread_wait.lock); + break; + } + __set_current_state(TASK_INTERRUPTIBLE); __add_wait_queue(&cc->write_thread_wait, &wait); spin_unlock_irq(&cc->write_thread_wait.lock); - if (unlikely(kthread_should_stop())) { - set_task_state(current, TASK_RUNNING); - remove_wait_queue(&cc->write_thread_wait, &wait); - break; - } - schedule(); - set_task_state(current, TASK_RUNNING); spin_lock_irq(&cc->write_thread_wait.lock); __remove_wait_queue(&cc->write_thread_wait, &wait); goto continue_locked; @@ -1531,8 +1530,13 @@ static void crypt_dtr(struct dm_target *ti) if (!cc) return; - if (cc->write_thread) + if (cc->write_thread) { + spin_lock_irq(&cc->write_thread_wait.lock); + set_bit(DM_CRYPT_EXIT_THREAD, &cc->flags); + wake_up_locked(&cc->write_thread_wait); + spin_unlock_irq(&cc->write_thread_wait.lock); kthread_stop(cc->write_thread); + } if (cc->io_queue) destroy_workqueue(cc->io_queue); |