linux-kernel - Re: [ANNOUNCE] 3.0.1-rt8

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Message-ID: <201108111804.11136.tim.sander@hbm.com>
Date:	Thu, 11 Aug 2011 18:04:10 +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>
Subject: Re: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7

Am Donnerstag, 11. August 2011, 14:41:38 schrieb Peter Zijlstra:
> On Thu, 2011-08-11 at 14:02 +0200, Peter Zijlstra wrote:
> > On Thu, 2011-08-11 at 13:30 +0200, Tim Sander wrote:
> > > The error does not occur  when configured with
> > > CONFIG_PREEMPT_RT_FULL=y
> > > but with
> > > CONFIG_PREEMPT_RTB=y.
> > > The same error also happens with
> > > CONFIG_PREEMPT_LL=y. (A log is appended after the other log just
> > > search for CONFIG_PREEMPT_LL
> > > for starting point).
> > 
> > Does the below (on top of -rt8) cure things for you? Shouldn't make a
> > difference for PREEMPT_LL though, so maybe there's something else busted
> > as well. But from what I can tell PREEMPT_BASE should be fine with such
> > things disabling preemption..
Yes it works for CONFIG_PREEMPT_RTB=y and as you say not for 
CONFIG_PREEMPT_LL=y.

However with the following patches on top of rt8:

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 44b3751..21ce185 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -22,7 +22,7 @@ static inline void raw_pagefault_enable(void)
        preempt_check_resched();
 }
 
-#ifndef CONFIG_PREEMPT_RT_FULL
+#ifndef CONFIG_PREEMPT_RT_BASE
 static inline void pagefault_disable(void)
 {
        raw_pagefault_disable();
diff --git a/mm/filemap.c b/mm/filemap.c
index 71e2a1f..af63de3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2040,7 +2040,7 @@ size_t iov_iter_copy_from_user_atomic(struct page *page,
        char *kaddr;
        size_t copied;
 
-       BUG_ON(!current->pagefault_disabled);
+       BUG_ON(!(in_atomic() || current->pagefault_disabled));
        kaddr = kmap_atomic(page, KM_USER0);
        if (likely(i->nr_segs == 1)) {
                int left;
diff --git a/mm/memory.c b/mm/memory.c
index cf71bd9..1b5a116 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3382,7 +3382,7 @@ unlock:
        return 0;
 }
 
-#ifdef CONFIG_PREEMPT_RT_FULL
+#ifdef CONFIG_PREEMPT_RT_BASE
 void pagefault_disable(void)
 {
        migrate_disable();

i get the following bug:

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 ]---

Otherwise the system boots and works

Best regards
Tim

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