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Date: Fri, 12 Aug 2011 10:59:19 +0200
From: "Tim Sander" <tim.sander@....com>
To: "Peter Zijlstra" <peterz@...radead.org>
Cc: "linux-kernel" <linux-kernel@...r.kernel.org>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Paul E. McKenney" <paulmck@...ibm.com>,
"linux-rt-users" <linux-rt-users@...r.kernel.org>,
"John Stultz" <johnstul@...ibm.com>
Subject: Re: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7
Am Donnerstag, 11. August 2011, 20:05:25 schrieb Peter Zijlstra:
> On Thu, 2011-08-11 at 18:14 +0200, Peter Zijlstra wrote:
> > On Thu, 2011-08-11 at 18:04 +0200, Tim Sander wrote:
> > > 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
>
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From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Thu Aug 11 19:18:23 CEST 2011
>
>
> Cc: john stultz <johnstul@...ibm.com>
> Reported-by: Tim Sander <tim.sander@....com>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Tested-by: Tim Sander <tim.sander@....com>
The Bug is gone with CONFIG_PREEMPT_LL=y and the patch below.
> ---
> 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;
> -
> - /* init the per-cpu posix_timer_tasklets */
> - for_each_cpu_mask(cpu, cpu_possible_map)
> - per_cpu(posix_timer_tasklist, cpu) = NULL;
>
> posix_timers_register_clock(CLOCK_PROCESS_CPUTIME_ID, &process);
> posix_timers_register_clock(CLOCK_THREAD_CPUTIME_ID, &thread);
>
> --
Best regards
Tim
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