diff options
author | Mike Isely <isely@pobox.com> | 2008-04-09 05:14:11 -0300 |
---|---|---|
committer | Mauro Carvalho Chehab <mchehab@infradead.org> | 2008-04-24 14:09:49 -0300 |
commit | 18ecbb4771eb0ecf297e996966b3c42f69cd6c02 (patch) | |
tree | 06978b91985fd4c1b092ec5ac8fef0b134eb18b3 /drivers/media/video | |
parent | 13e027a8bf2a507334fa0d30246ce619ff581cbb (diff) | |
download | op-kernel-dev-18ecbb4771eb0ecf297e996966b3c42f69cd6c02.zip op-kernel-dev-18ecbb4771eb0ecf297e996966b3c42f69cd6c02.tar.gz |
V4L/DVB (7714): pvrusb2: Fix hang on module removal
The pvrusb2 driver was getting had by this scenario:
1. Task A calls kthread_stop() for task B.
2. Before exiting, then Task B calls kthread_stop() for task C.
The problem is, kthread_stop() wants to allocate an internal resource
to itself (i.e. acquire a lock), which won't be released until
kthread_stop() returns. But kthread_stop() won't return until task B
is dead. But task B won't die until it finishes its call to
kthread_stop() for task C, and that will block waiting on the resource
already allocated inside task A. Deadlock.
With the pvrusb2 driver, task A is the caller to pvr_exit(), task B is
the control thread run inside of pvrusb2-context.c, and task C is any
worker thread run inside of pvrusb2-hdw.c.
This problem got introduced by the previous threading setup change,
which was itself an attempt to fix a module tear-down race (which it
actually did fix). The lesson here is that a task being waited on as
part of a kthread_stop() simply cannot be allow to also issue a
kthread_stop() - or we make sure not to issue the enclosing
kthread_stop() until we know that the inner kthread_stop() has
completed first. The solution for the pvrusb2 driver is some hackish
code which changes the main control thread tear down into a two step
process. This then makes it possible to delay issuing the
kthread_stop() on the control thread until after we know that
everything has been torn down first. (And yes, we really need that
kthread_stop() because it's the only way to safely guarantee that a
module-referencing kernel thread has safely returned back out of the
module before we finally remove the module.)
Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Diffstat (limited to 'drivers/media/video')
-rw-r--r-- | drivers/media/video/pvrusb2/pvrusb2-context.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/drivers/media/video/pvrusb2/pvrusb2-context.c b/drivers/media/video/pvrusb2/pvrusb2-context.c index e7a2ed5..a2ce022 100644 --- a/drivers/media/video/pvrusb2/pvrusb2-context.c +++ b/drivers/media/video/pvrusb2/pvrusb2-context.c @@ -35,6 +35,9 @@ static struct pvr2_context *pvr2_context_notify_first; static struct pvr2_context *pvr2_context_notify_last; static DEFINE_MUTEX(pvr2_context_mutex); static DECLARE_WAIT_QUEUE_HEAD(pvr2_context_sync_data); +static DECLARE_WAIT_QUEUE_HEAD(pvr2_context_cleanup_data); +static int pvr2_context_cleanup_flag; +static int pvr2_context_cleaned_flag; static struct task_struct *pvr2_context_thread_ptr; @@ -153,7 +156,7 @@ static void pvr2_context_check(struct pvr2_context *mp) static int pvr2_context_shutok(void) { - return kthread_should_stop() && (pvr2_context_exist_first == NULL); + return pvr2_context_cleanup_flag && (pvr2_context_exist_first == NULL); } @@ -174,6 +177,15 @@ static int pvr2_context_thread_func(void *foo) pvr2_context_shutok())); } while (!pvr2_context_shutok()); + pvr2_context_cleaned_flag = !0; + wake_up(&pvr2_context_cleanup_data); + + pvr2_trace(PVR2_TRACE_CTXT,"pvr2_context thread cleaned up"); + + wait_event_interruptible( + pvr2_context_sync_data, + kthread_should_stop()); + pvr2_trace(PVR2_TRACE_CTXT,"pvr2_context thread end"); return 0; @@ -191,6 +203,11 @@ int pvr2_context_global_init(void) void pvr2_context_global_done(void) { + pvr2_context_cleanup_flag = !0; + wake_up(&pvr2_context_sync_data); + wait_event_interruptible( + pvr2_context_cleanup_data, + pvr2_context_cleaned_flag); kthread_stop(pvr2_context_thread_ptr); } |