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    SubjectRe: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7
    Date
    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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