Messages in this thread | | | Date | Sun, 5 Oct 2008 08:11:45 -0700 | From | Arjan van de Ven <> | Subject | Re: [kerneloops] regression in 2.6.27 wrt "lock_page" and the "hwclock" program |
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On Sat, 4 Oct 2008 21:52:25 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> 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()?
static unsigned long atomic(const char *name, unsigned long (*op)(unsigned long), unsigned long arg) { unsigned long v; __asm__ volatile ("cli"); v = (*op)(arg); __asm__ volatile ("sti"); return v; }
looks like it (but only on 32 bit x86, not on 64 bit x86)
> > 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.
or save - enable - <run handlers> - restore sequence
it's horrible that we allowed this before, and the semantics are very fuzzy at best, but to go WARN_ON() for it might be a bit too much.
(and yes someone really ought to fix hwclock; it's rather broken)
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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