@@ -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);
This is a note to let you know that I have just added a patch titled dm crypt: fix a possible hang due to race condition on exit to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue This patch is scheduled to be released in version 4.2.8-ckt2. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 4.2.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ---8<------------------------------------------------------------ From aebe441cdf0ef0f6554e98dbc996dc62da76e80c Mon Sep 17 00:00:00 2001 From: Mikulas Patocka <mpatocka@redhat.com> Date: Thu, 19 Nov 2015 07:36:50 -0500 Subject: dm crypt: fix a possible hang due to race condition on exit commit bcbd94ff481ec1d7b5c824d90df82d0faafabd35 upstream. 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> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- drivers/md/dm-crypt.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) -- 1.9.1