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authorMikulas Patocka <mpatocka@redhat.com>2015-11-19 07:36:50 -0500
committerMike Snitzer <snitzer@redhat.com>2015-11-19 13:38:30 -0500
commitbcbd94ff481ec1d7b5c824d90df82d0faafabd35 (patch)
treeac755d832487bd9cce6ee61ac319be6ed09574e9 /drivers/md/dm-crypt.c
parent43e43c9ea60a7a1831ec823773e924d2dadefd44 (diff)
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-crypt.c')
-rw-r--r--drivers/md/dm-crypt.c22
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);