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SubjectRe: [kerneloops] regression in 2.6.27 wrt "lock_page" and the "hwclock" program
On Sat, 4 Oct 2008 17:44:33 -0700 Arjan van de Ven <arjan@infradead.org> wrote:

>
> Details: http://www.kerneloops.org/searchweek.php?search=lock_page
>
> There's quite a few of this BUG, which seems to be an interaction between the "hwclock" program and something in 2.6.27.
> It's new in .27 and is currently the 8th ranked issue.....
>
> BUG: sleeping function called from invalid context at
> include/linux/pagemap.h:294 in_atomic():0, irqs_disabled():1
> INFO: lockdep is turned off.
> irq event stamp: 0
> hardirqs last enabled at (0): [<00000000>] 0x0
> hardirqs last disabled at (0): [<c042c3a4>] copy_process+0x2e7/0x115e
> softirqs last enabled at (0): [<c042c3a4>] copy_process+0x2e7/0x115e
> softirqs last disabled at (0): [<00000000>] 0x0
> Pid: 9591, comm: hwclock Tainted: G W 2.6.27-0.372.rc8.fc10.i686 #1
> [<c0427a53>] __might_sleep+0xd1/0xd6
> [<c0479a8b>] lock_page+0x1a/0x34
> [<c0479cfa>] find_lock_page+0x23/0x48
> [<c047a215>] filemap_fault+0x9b/0x330
> [<c0486493>] __do_fault+0x40/0x2e6
> [<c0487d63>] handle_mm_fault+0x2ec/0x6d2
> [<c06e8260>] do_page_fault+0x2e5/0x693
>

Looks like `hwclock' disabled interrupts in userspace with sys_iopl()?

And then it took a pagefault, which is presumably a bug in hwclock.

That's all a bit antisocial of it. I guess a suitable quickfix is to
remove the might_sleep() from lock_page() (which would be a good thing
from a text size POV anyway).

But there will of course be other sites which do possibly-sleeping
operations on the pagefault path.

Really, it's a bit stupid doing _any_ system calls (and a pagefault is
a syscall in disguise) with interrupts disabled. The kernel makes no
guarantees that we'll honour it. We could just enable interrupts on
pagefault entry - that'll teach 'em.



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