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    SubjectRe: 2.6.24-rc8-mm1: powerpc oopses
    On Thu, 17 Jan 2008 23:15:27 +0100
    Mariusz Kozlowski <m.kozlowski@tuxland.pl> wrote:

    > Hello,
    >
    > The script below kills powerpc. oopses get longer and more
    > wonderful with every next 'cated' file.

    ppc32.

    > /proc/<pid>/task/<pid>/pagemap seems to be the cause of oops. The
    > important thing is that it oopses for random (that is not first in a row)
    > process from /proc. So not every 'cat /proc/<pid>/task/<pid>/pagemap'
    > causes an oops.
    >
    > I could try to bisect this but this powerpc box is iMac G3 (cpu at 400MHz)
    > and this will take time. So any hints appreciated.
    >
    > Regards,
    >
    > Mariusz
    >
    > script:
    > ---------
    > #!/bin/bash
    >
    > for i in `find /proc/*/ -readable -type f`; do
    > echo -n "cat $i > /dev/null ... ";
    > logger -t proc_loop $i;
    > sync;
    > cat $i > /dev/null;
    > echo "done";
    > done
    > ----------
    > syslog:
    > proc_loop: /proc/3731/task/3731/pagemap
    > kernel: BUG: sleeping function called from invalid context at fs/proc/task_mmu.c:554
    > kernel: in_atomic():1, irqs_disabled():0
    > kernel: Call Trace:
    > kernel: [cf1cddf0] [c000840c] show_stack+0x3c/0x194 (unreliable)
    > kernel: [cf1cde20] [c002b2ec] __might_sleep+0xf4/0x108
    > kernel: [cf1cde30] [c00d2d54] add_to_pagemap+0x40/0x11c
    > kernel: [cf1cde50] [c00d2f44] pagemap_pte_range+0xa8/0x10c
    > kernel: [cf1cde70] [c0081b30] walk_page_range+0x148/0x23c
    > kernel: [cf1cdeb0] [c00d3104] pagemap_read+0x15c/0x244
    > kernel: [cf1cdef0] [c0092144] vfs_read+0xc4/0x16c
    > kernel: [cf1cdf10] [c009261c] sys_read+0x4c/0x90
    > kernel: [cf1cdf40] [c001328c] ret_from_syscall+0x0/0x40

    It's not really an oops - it's a warning. add_to_pagemap() is doing a
    put_user() inside pagemap_pte_range->pte_offset_map->kmap_atomic.

    A known bug, I'm afraid.

    How to fix?

    - double-buffer the data to be copied to userspace or

    - take a local copy of the pte page then work on that instead or

    - play copy_to_user_inatomic() tricks.

    It would be really nice to get the maps4 stuff merged this time around but
    it is looking unlikely.

    > kernel: --- Exception: c01 at 0xff5a364
    > kernel: LR = 0x10002f60
    > kernel: BUG: scheduling while atomic: cat/8929/0x00000002
    > kernel: Call Trace:
    > kernel: [cf1cde90] [c000840c] show_stack+0x3c/0x194 (unreliable)
    > kernel: [cf1cdec0] [c002db24] __schedule_bug+0x64/0x78
    > kernel: [cf1cdee0] [c027207c] schedule+0x304/0x32c
    > kernel: [cf1cdf40] [c0013a5c] recheck+0x0/0x28
    > kernel: --- Exception: c01 at 0xff5a364
    > kernel: LR = 0x10002f60
    > kernel: BUG: scheduling while atomic: cat/8929/0x00000007
    > kernel: Call Trace:
    > kernel: [cf1cde90] [c000840c] show_stack+0x3c/0x194 (unreliable)
    > kernel: [cf1cdec0] [c002db24] __schedule_bug+0x64/0x78
    > kernel: [cf1cdee0] [c027207c] schedule+0x304/0x32c
    > kernel: [cf1cdf40] [c0013a5c] recheck+0x0/0x28
    > kernel: --- Exception: c01 at 0xff5a364
    > kernel: LR = 0x10002f60
    > kernel: BUG: scheduling while atomic: cat/8929/0x00000009
    > kernel: Call Trace:
    > kernel: [cf1cde90] [c000840c] show_stack+0x3c/0x194 (unreliable)
    > kernel: [cf1cdec0] [c002db24] __schedule_bug+0x64/0x78
    > kernel: [cf1cdee0] [c027207c] schedule+0x304/0x32c
    > kernel: [cf1cdf40] [c0013a5c] recheck+0x0/0x28
    > kernel: --- Exception: c01 at 0xff5a364
    > kernel: LR = 0x10002f60
    > kernel: Page fault in user mode with in_atomic() = 1 mm = cf2765a0
    > kernel: NIP = ff0cbc8 MSR = 4000f932
    > kernel: Oops: Weird page fault, sig: 11 [#3]

    hm. Not sure how that happened. The arch code thinks we're running in
    user mode.

    > kernel: PREEMPT PowerMac
    > kernel: Modules linked in: usbhid ide_cd_mod ohci_hcd usbcore uninorth_agp agpgart
    > kernel: NIP: 0ff0cbc8 LR: 0ff0d398 CTR: 0ff0d2d0
    > kernel: REGS: cf1cdf50 TRAP: 0401 Tainted: G D (2.6.24-rc8-mm1)
    > kernel: MSR: 4000f932 <EE,PR,FP,ME,IR,DR> CR: 28022442 XER: 00000000
    > kernel: TASK = cf8d74f0[8929] 'cat' THREAD: cf1cc000
    > kernel: GPR00: 00000001 bf93e330 48029bf0 0ffed488 10016038 28022442 00000000 0ff5a364
    > kernel: GPR08: 0000f932 00000000 00001032 00000000 28022442
    > kernel: NIP [0ff0cbc8] 0xff0cbc8
    > kernel: LR [0ff0d398] 0xff0d398
    > proc_loop: /proc/3731/task/3731/wchan
    > kernel: Call Trace:
    > kernel: ---[ end trace 54bd1ed4883922c9 ]---
    > kernel: note: cat[8929] exited with preempt_count 10
    > proc_loop: /proc/3731/task/3731/oom_score
    > proc_loop: /proc/3731/task/3731/oom_adj
    > proc_loop: /proc/3731/fdinfo/0
    > [... snip ...]


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