Re: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7

On Thu, 2011-08-11 at 18:14 +0200, Peter Zijlstra wrote:

On Thu, 2011-08-11 at 18:04 +0200, Tim Sander wrote:

quoted

kernel BUG at kernel/posix-cpu-timers.c:1315!
Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 817 [#1] PREEMPT
Modules linked in: i2c_imx(+) netx netx_reset dspload fpgaload mxc_nand(+) nand nand_ids nand_ecc
CPU: 0    Not tainted  (3.0.0-pmx-rt8-00009-g39305ab #167)
PC is at __bug+0x24/0x30
LR is at walk_stackframe+0x24/0x40
pc : [<c002cbf0>]    lr : [<c002cbb0>]    psr: 60000113
sp : c782ff40  ip : c782fe28  fp : c782ff4c
r10: 00000001  r9 : 00000000  r8 : c78663c0
r7 : c030463c  r6 : c782e000  r5 : 00000000  r4 : c78663c0
r3 : 00000000  r2 : 00000001  r1 : c782fe58  r0 : 00000034
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
Control: 00c5387d  Table: 87b70008  DAC: 00000017
Process posixcputmr/0 (pid: 6, stack limit = 0xc782e268)
Stack: (0xc782ff40 to 0xc7830000)
ff40: c782ff8c c782ff50 c005a5c0 c002cbd8 00000000 c782ff54 c782ff54 00000000
ff60: 00000000 c78663c0 00000000 c782e000 c030463c c78663c0 00000000 00000001
ff80: c782ffbc c782ff90 c005a88c c005a594 00000000 c7817f28 00000000 c782ffcc
ffa0: c005a800 00000000 00000000 00000000 c782fff4 c782ffc0 c00570f0 c005a80c
ffc0: c7817f28 00000000 00000000 00000000 c782ffd0 c782ffd0 c7817f28 c0057064
ffe0: c0040868 00000013 00000000 c782fff8 c0040868 c0057070 cccdcd6c ffdec890
Backtrace: 
[<c002cbcc>] (__bug+0x0/0x30) from [<c005a5c0>] (__run_posix_cpu_timers+0x38/0x278)
[<c005a588>] (__run_posix_cpu_timers+0x0/0x278) from [<c005a88c>] (posix_cpu_timers_thread+0x8c/0x124)
[<c005a800>] (posix_cpu_timers_thread+0x0/0x124) from [<c00570f0>] (kthread+0x8c/0x94)
[<c0057064>] (kthread+0x0/0x94) from [<c0040868>] (do_exit+0x0/0x2d8)
 r7:00000013 r6:c0040868 r5:c0057064 r4:c7817f28
Code: e59f0010 e1a01003 eb086a88 e3a03000 (e5833000) 
---[ end trace d632afeaa11559d4 ]--- 

Yay a new one, and this is a PREEMPT_LL build right? /me goes poke at
it.

---
Subject: posix-cpu-timer: Fixup PREEMPT_LL build
From: Peter Zijlstra <redacted>
Date: Thu Aug 11 19:18:23 CEST 2011


Cc: john stultz <redacted>
Reported-by: Tim Sander <redacted>
Signed-off-by: Peter Zijlstra <redacted>
---
 include/linux/init_task.h |    8 +++++++-
 include/linux/sched.h     |    2 ++
 kernel/fork.c             |    2 ++
 kernel/posix-cpu-timers.c |   24 ++++++++++++++++--------
 4 files changed, 27 insertions(+), 9 deletions(-)

Index: linux-2.6/include/linux/init_task.h
===================================================================

--- linux-2.6.orig/include/linux/init_task.h
+++ linux-2.6/include/linux/init_task.h

@@ -126,6 +126,12 @@ extern struct cred init_cred;
 # define INIT_PERF_EVENTS(tsk)
 #endif
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+# define INIT_TIMER_LIST		.posix_timer_list = NULL,
+#else
+# define INIT_TIMER_LIST
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)

@@ -179,7 +185,7 @@ extern struct cred init_cred;
 	.fs_excl	= ATOMIC_INIT(0),				\
 	.pi_lock	= __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock),	\
 	.timer_slack_ns = 50000, /* 50 usec default slack */		\
-	.posix_timer_list = NULL,					\
+	INIT_TIMER_LIST							\
 	.pids = {							\
 		[PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),		\
 		[PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),		\

Index: linux-2.6/include/linux/sched.h
===================================================================

--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h

@@ -1364,7 +1364,9 @@ struct task_struct {
 
 	struct task_cputime cputime_expires;
 	struct list_head cpu_timers[3];
+#ifdef CONFIG_PREEMPT_RT_BASE
 	struct task_struct *posix_timer_list;
+#endif
 
 /* process credentials */
 	const struct cred __rcu *real_cred; /* objective and real subjective task

Index: linux-2.6/kernel/fork.c
===================================================================

--- linux-2.6.orig/kernel/fork.c
+++ linux-2.6/kernel/fork.c

@@ -1054,7 +1054,9 @@ void mm_init_owner(struct mm_struct *mm,
  */
 static void posix_cpu_timers_init(struct task_struct *tsk)
 {
+#ifdef CONFIG_PREEMPT_RT_BASE
 	tsk->posix_timer_list = NULL;
+#endif
 	tsk->cputime_expires.prof_exp = cputime_zero;
 	tsk->cputime_expires.virt_exp = cputime_zero;
 	tsk->cputime_expires.sched_exp = 0;

Index: linux-2.6/kernel/posix-cpu-timers.c
===================================================================

--- linux-2.6.orig/kernel/posix-cpu-timers.c
+++ linux-2.6/kernel/posix-cpu-timers.c

@@ -1370,6 +1370,7 @@ static void __run_posix_cpu_timers(struc
 	}
 }
 
+#ifdef CONFIG_PREEMPT_RT_BASE
 #include <linux/kthread.h>
 #include <linux/cpu.h>
 DEFINE_PER_CPU(struct task_struct *, posix_timer_task);

@@ -1532,14 +1533,26 @@ static struct notifier_block __devinitda
 
 static int __init posix_cpu_thread_init(void)
 {
-	void *cpu = (void *)(long)smp_processor_id();
+	void *hcpu = (void *)(long)smp_processor_id();
 	/* Start one for boot CPU. */
-	posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_UP_PREPARE, cpu);
-	posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_ONLINE, cpu);
+	unsigned long cpu;
+
+	/* init the per-cpu posix_timer_tasklets */
+	for_each_cpu_mask(cpu, cpu_possible_map)
+		per_cpu(posix_timer_tasklist, cpu) = NULL;
+
+	posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_UP_PREPARE, hcpu);
+	posix_cpu_thread_call(&posix_cpu_thread_notifier, CPU_ONLINE, hcpu);
 	register_cpu_notifier(&posix_cpu_thread_notifier);
 	return 0;
 }
 early_initcall(posix_cpu_thread_init);
+#else /* CONFIG_PREEMPT_RT_BASE */
+void run_posix_cpu_timers(struct task_struct *tsk)
+{
+	__run_posix_cpu_timers(tsk);
+}
+#endif /* CONFIG_PREEMPT_RT_BASE */
 
 /*
  * Set one of the process-wide special case CPU timers or RLIMIT_CPU.

@@ -1789,11 +1802,6 @@ static __init int init_posix_cpu_timers(
 		.timer_create	= thread_cpu_timer_create,
 	};
 	struct timespec ts;
-	unsigned long cpu;