2014-10-30 01:32:38

by Sasha Levin

Subject: [PATCH] Bluetooth: Revert "Bluetooth: rfcomm: Remove unnecessary krfcommd event"

This reverts commit e5842cdb0f4f2c68f6acd39e286e5d10d8c073e8.

We can't call rfcomm_process_sessions() while our task state is not
TASK_RUNNING since rfcomm_process_sessions() tries to lock mutexes
and sleep. The scheduler even complains about it:

[ 21.683959] WARNING: CPU: 13 PID: 8165 at kernel/sched/core.c:7305 __might_sleep+0xe5/0x1b0()
[ 21.683962] do not call blocking ops when !TASK_RUNNING; state=1 set at rfcomm_run (net/bluetooth/rfcomm/core.c:2096)
[ 21.683963] Modules linked in:
[ 21.683966] CPU: 13 PID: 8165 Comm: krfcommd Tainted: G W 3.18.0-rc2-next-20141029-sasha-00035-gd14bbcb-dirty #1425
[ 21.683969] ffffffffae2b4d0e 0000000000000000 ffff8805c0b23c00 ffff8805c0b23b98
[ 21.683972] ffffffffad010b76 0000000000000000 ffff8805c0b23bf8 ffff8805c0b23be8
[ 21.683975] ffffffffa3298dd8 ffffffffad0a0910 ffffffffa3309f95 ffff8805c0b23bc8
[ 21.683976] Call Trace:
[ 21.683979] dump_stack (lib/dump_stack.c:52)
[ 21.683982] warn_slowpath_common (kernel/panic.c:432)
[ 21.683985] ? __schedule (kernel/sched/core.c:2840)
[ 21.683987] ? __might_sleep (kernel/sched/core.c:7311)
[ 21.683990] warn_slowpath_fmt (kernel/panic.c:446)
[ 21.683993] ? rfcomm_run (net/bluetooth/rfcomm/core.c:2096)
[ 21.683996] ? rfcomm_run (net/bluetooth/rfcomm/core.c:2096)
[ 21.683999] __might_sleep (kernel/sched/core.c:7311)
[ 21.684002] mutex_lock_nested (kernel/locking/mutex.c:508 kernel/locking/mutex.c:622)
[ 21.684004] ? __schedule (./arch/x86/include/asm/bitops.h:311 include/linux/thread_info.h:91 include/linux/sched.h:2937 kernel/sched/core.c:2845)
[ 21.684008] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
[ 21.684011] rfcomm_run (net/bluetooth/rfcomm/core.c:1990 net/bluetooth/rfcomm/core.c:2102)
[ 21.684014] ? preempt_count_sub (kernel/sched/core.c:2641)
[ 21.684017] ? __schedule (./arch/x86/include/asm/bitops.h:311 include/linux/thread_info.h:91 include/linux/sched.h:2937 kernel/sched/core.c:2845)
[ 21.684020] ? rfcomm_process_rx (net/bluetooth/rfcomm/core.c:2088)
[ 21.684023] ? rfcomm_process_rx (net/bluetooth/rfcomm/core.c:2088)
[ 21.684025] kthread (kernel/kthread.c:207)
[ 21.684029] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2559 kernel/locking/lockdep.c:2601)
[ 21.684032] ? flush_kthread_work (kernel/kthread.c:176)
[ 21.684035] ret_from_fork (arch/x86/kernel/entry_64.S:348)
[ 21.684038] ? flush_kthread_work (kernel/kthread.c:176)

Instead, just go to the old way oftracking wakeups.

Signed-off-by: Sasha Levin <[email protected]>
---
net/bluetooth/rfcomm/core.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index bce9c3d..942de7765 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -48,6 +48,7 @@ static DEFINE_MUTEX(rfcomm_mutex);
#define rfcomm_lock() mutex_lock(&rfcomm_mutex)
#define rfcomm_unlock() mutex_unlock(&rfcomm_mutex)

+static unsigned long rfcomm_event;

static LIST_HEAD(session_list);

@@ -105,6 +106,7 @@ static void rfcomm_schedule(void)
{
if (!rfcomm_thread)
return;
+ set_bit(RFCOMM_SCHED_WAKEUP, &rfcomm_event);
wake_up_process(rfcomm_thread);
}

@@ -2092,18 +2094,19 @@ static int rfcomm_run(void *unused)

rfcomm_add_listener(BDADDR_ANY);

- while (1) {
+ while (!kthread_should_stop()) {
set_current_state(TASK_INTERRUPTIBLE);
-
- if (kthread_should_stop())
- break;
+ if (!test_bit(RFCOMM_SCHED_WAKEUP, &rfcomm_event)) {
+ /* No pending events. Let's sleep.
+ * Incoming connections and data will wake us up. */
+ schedule();
+ }
+ set_current_state(TASK_RUNNING);

/* Process stuff */
+ clear_bit(RFCOMM_SCHED_WAKEUP, &rfcomm_event);
rfcomm_process_sessions();
-
- schedule();
}
- __set_current_state(TASK_RUNNING);

rfcomm_kill_listener();

--
1.7.10.4

2014-10-30 02:06:25

by Peter Hurley

Subject: Re: [PATCH] Bluetooth: Revert "Bluetooth: rfcomm: Remove unnecessary krfcommd event"

Hi Sasha,

On 10/29/2014 09:32 PM, Sasha Levin wrote:
> This reverts commit e5842cdb0f4f2c68f6acd39e286e5d10d8c073e8.
>
> We can't call rfcomm_process_sessions() while our task state is not
> TASK_RUNNING since rfcomm_process_sessions() tries to lock mutexes
> and sleep. The scheduler even complains about it:
>
> [ 21.683959] WARNING: CPU: 13 PID: 8165 at kernel/sched/core.c:7305 __might_sleep+0xe5/0x1b0()
> [ 21.683962] do not call blocking ops when !TASK_RUNNING; state=1 set at rfcomm_run (net/bluetooth/rfcomm/core.c:2096)

This problem is in-process with Peter Z and Oleg and a new api
for handling nested sleeps.

The thread is here
http://www.gossamer-threads.com/lists/linux/kernel/2019181?do=post_view_threaded
and the reminder thread here
https://lkml.org/lkml/2014/10/27/343

Regards,
Peter Hurley